NCERT Class 9 Science Solutions: Matter in Our Surroundings
Question:
Why is ice at 273 K more effective in cooling than water at the same temperature?
Concept in a Minute:
The key concept here is the difference between sensible heat and latent heat. Sensible heat is the heat absorbed or released by a substance that changes its temperature. Latent heat is the heat absorbed or released by a substance that changes its state (e.g., solid to liquid, liquid to gas) at a constant temperature. Specifically, for cooling, we are interested in the latent heat of fusion.
Explanation:
Ice at 273 K (which is 0°C) requires a significant amount of energy to change its state from solid (ice) to liquid (water). This energy is called the latent heat of fusion. When ice comes into contact with a warmer object, it absorbs heat from that object to melt. This absorption of heat causes the temperature of the object to decrease.
Water at 273 K (0°C) has already undergone the phase change from ice to water. Therefore, it no longer needs to absorb latent heat to melt. If it were to cool something, it would only do so by absorbing sensible heat, which is the heat required to lower its own temperature. Since ice absorbs latent heat in addition to any sensible heat it might absorb (as it warms up before melting), it has a greater capacity to extract heat from its surroundings, making it more effective at cooling.
In essence, ice at 273 K absorbs heat to melt and become water at 273 K. This process of melting uses up a considerable amount of heat energy. Water at 273 K, being already in liquid form, does not undergo this phase change and thus absorbs much less heat for the same temperature change.
Question:
Suggest a method to liquefy atmospheric gases.
Concept in a Minute:
Liquefaction of gases relies on reducing the kinetic energy of gas molecules and bringing them closer together. This can be achieved by lowering temperature and/or increasing pressure.
Explanation:
To liquefy atmospheric gases, which are primarily nitrogen and oxygen, we need to bring them to a state where their molecules are close enough to attract each other and form a liquid. This is accomplished by a two-step process involving cooling and compression.
Step 1: Compression
The atmospheric air is first compressed to a high pressure. This increases the frequency of collisions between gas molecules and forces them closer together, which in turn increases their potential energy and favors liquefaction.
Step 2: Cooling
After compression, the gas is rapidly expanded. This expansion causes a significant drop in temperature (Joule-Thomson effect). Alternatively, the compressed gas can be passed through a cooling system, often using refrigeration techniques or liquid air from a previous cycle. The objective is to cool the gas below its critical temperature.
As the temperature is lowered sufficiently, the kinetic energy of the gas molecules decreases to a point where the intermolecular forces of attraction become dominant, causing the gas to condense into a liquid.
Therefore, a method to liquefy atmospheric gases is to compress them to a high pressure and then cool them down significantly, below their respective critical temperatures. This process is commonly carried out in air separation units.
Question:
Which of the following are matter?
Chair, air, love, smell, hate, almonds, thought, cold, lemon water, smell of perfume.
Concept in a Minute:
Matter is anything that has mass and occupies space.
Explanation:
To determine if something is matter, we need to check if it has mass (weighs something) and takes up space.
Let’s analyze each item:
Chair: Has mass and occupies space. Therefore, it is matter.
Air: Although invisible, air has mass (e.g., a balloon filled with air is heavier than an empty one) and occupies space. Therefore, it is matter.
Love: An emotion. It has no mass and does not occupy space. Therefore, it is not matter.
Smell: A sensation perceived by the nose. While smells are caused by particles (molecules), the smell itself is not a physical substance with mass. Therefore, it is not matter.
Hate: An emotion. It has no mass and does not occupy space. Therefore, it is not matter.
Almonds: Solid objects. They have mass and occupy space. Therefore, they are matter.
Thought: A mental process. It has no mass and does not occupy space. Therefore, it is not matter.
Cold: A state of low temperature, a sensation. It is the absence of heat. It does not have mass or occupy space. Therefore, it is not matter.
Lemon water: A mixture of water and lemon juice. Both water and lemon juice are made of molecules that have mass and occupy space. Therefore, lemon water is matter.
Smell of perfume: Similar to “smell” above, the smell itself is a sensation. The perfume molecules that cause the smell are matter, but the “smell of perfume” as a concept is not. Therefore, it is not matter.
List of Matter:
Chair, air, almonds, lemon water.
Question:
Why are we able to sip hot tea or milk faster from a saucer than a cup?
Concept in a Minute:
Evaporation: The process where a liquid changes into a gas or vapor. This process requires heat energy.
Surface Area: The extent of a two-dimensional surface that an object possesses. A larger surface area allows for more interaction with the surroundings.
Heat Transfer: The movement of thermal energy from a region of higher temperature to a region of lower temperature.
Explanation:
We are able to sip hot tea or milk faster from a saucer than a cup because of the difference in their surface areas exposed to the air.
A saucer has a much larger surface area compared to the opening of a cup. Hot liquids lose heat primarily through evaporation and convection.
Evaporation is the process where the liquid turns into vapor and escapes into the air. This process requires heat energy, which is drawn from the liquid itself, thus cooling it down. A larger surface area allows for a greater rate of evaporation because more liquid molecules are in contact with the air and can escape as vapor.
Convection is the transfer of heat through the movement of fluids (in this case, the hot liquid and the surrounding air). While both the cup and saucer experience convection, the increased surface area of the saucer leads to more efficient heat loss to the surrounding air.
Therefore, the hot tea or milk in a saucer cools down much faster than in a cup due to the significantly larger surface area available for evaporation and convection, allowing us to drink it sooner.
Question:
Give two reasons to justify water at room temperature is a liquid.
Concept in a Minute:
States of Matter, Intermolecular Forces, Kinetic Energy, Boiling Point, Melting Point
Explanation:
Water at room temperature (approximately 20-25°C or 293-298 K) exists as a liquid due to the balance between the kinetic energy of its molecules and the strength of the intermolecular forces holding them together.
Two reasons to justify water at room temperature being a liquid are:
1. Intermolecular Forces: Water molecules are held together by strong hydrogen bonds. These forces are significant enough to prevent the molecules from separating completely into a gas, but not so strong that they lock the molecules into a fixed, rigid structure like a solid. The hydrogen bonds are constantly breaking and reforming, allowing water molecules to slide past each other, which is characteristic of a liquid.
2. Kinetic Energy vs. Intermolecular Forces: At room temperature, the kinetic energy of water molecules (the energy of motion) is sufficient to overcome some of the intermolecular forces, allowing for movement and fluidity. However, this kinetic energy is not high enough to completely overcome all the attractive forces and allow the molecules to escape into the gaseous state. In other words, water’s boiling point (100°C) is significantly higher than room temperature, and its melting point (0°C) is significantly lower than room temperature. This places room temperature within the liquid phase of water.
Question:
Convert the following temperature to the celsius scale.
293 K
Concept in a Minute:
The relationship between Kelvin (K) and Celsius (C) temperature scales. The Kelvin scale is an absolute temperature scale where 0 K represents absolute zero. The Celsius scale is a relative temperature scale where 0°C is the freezing point of water and 100°C is the boiling point of water at standard atmospheric pressure. The conversion formula between Kelvin and Celsius is: K = C + 273.15 or C = K – 273.15. For most high school purposes, 273 is often used as an approximation.
Explanation:
The question asks to convert a temperature from the Kelvin scale to the Celsius scale. We are given the temperature in Kelvin as 293 K. The formula to convert Kelvin to Celsius is:
Celsius = Kelvin – 273.15
Using the given value:
Celsius = 293 K – 273.15
Calculating the result:
Celsius = 19.85°C
If we use the approximation 273 for 273.15:
Celsius = 293 K – 273
Celsius = 20°C
Therefore, 293 K is equal to 19.85°C or approximately 20°C.
Detailed Steps:
1. Identify the given temperature: The temperature is given as 293 K.
2. Recall the conversion formula between Kelvin and Celsius: The formula is C = K – 273.15.
3. Substitute the given Kelvin temperature into the formula: C = 293 – 273.15.
4. Perform the subtraction: C = 19.85.
5. State the answer with the correct unit: The temperature is 19.85°C.
6. Consider the approximation if applicable: If using 273 as the conversion factor, C = 293 – 273 = 20°C.
Question:
Give two reasons to justify an iron almirah is a solid at room temperature.
Concept in a Minute:
States of Matter: Solids, liquids, and gases are the three common states of matter. Solids have a definite shape and volume, liquids have a definite volume but take the shape of their container, and gases have neither a definite shape nor a definite volume. Properties of Solids: Solids are characterized by strong intermolecular forces, fixed positions of particles, and resistance to deformation.
Explanation:
An iron almirah is considered a solid at room temperature for the following two reasons:
1. Definite Shape and Volume: At room temperature, an iron almirah maintains its specific shape and occupies a fixed amount of space. It does not spread out to fill its surroundings like a gas, nor does its shape change easily if it is placed in a different container, unlike a liquid. This characteristic of possessing a definite shape and a definite volume is a hallmark of a solid.
2. Rigidity and Incompressibility: Iron is a rigid material, meaning it resists changes in its shape when a force is applied. An iron almirah is very difficult to compress; its volume does not significantly decrease even under considerable pressure. This high degree of rigidity and incompressibility arises from the strong intermolecular forces between the iron atoms, which hold them in fixed positions within a lattice structure. These properties are characteristic of the solid state.
Question:
What is the physical state of water at 100°C.
Concept in a Minute:
The physical state of a substance is determined by its temperature and pressure. For water, key temperatures include the melting point (0°C) and the boiling point (100°C at standard atmospheric pressure). Below the melting point, water is solid (ice). Between the melting point and boiling point, water is liquid. At and above the boiling point, water exists as a gas (steam).
Explanation:
At 100°C, water is at its boiling point under standard atmospheric pressure. When water reaches its boiling point, it absorbs heat energy and undergoes a phase transition from a liquid to a gas, which is called steam. Therefore, the physical state of water at 100°C is gaseous.
Detailed Solution Structure:
1. Identify the substance: The question is about water.
2. Identify the given condition: The temperature is 100°C.
3. Recall the phase transition points of water:
a. Melting point (solid to liquid): 0°C
b. Boiling point (liquid to gas): 100°C (at standard atmospheric pressure)
4. Compare the given temperature with the phase transition points: The given temperature of 100°C is equal to the boiling point of water.
5. Determine the physical state at the boiling point: At the boiling point, water transitions from liquid to gas. Therefore, at 100°C, water exists as a gas (steam).
6. Conclude the physical state: The physical state of water at 100°C is gaseous.
Question:
Give reasons:
A gas fills completely the vessel in which it is kept.
Concept in a Minute:
Kinetic Molecular Theory of Gases: This theory describes gases as being composed of a large number of tiny particles (atoms or molecules) that are in constant, random motion. These particles have a large average distance between them and exert negligible attractive forces on each other.
Explanation:
A gas completely fills the vessel it is kept in because of the nature of its constituent particles as described by the Kinetic Molecular Theory.
1. Large Intermolecular Spaces: Gas particles are very far apart compared to their size. This means there are vast empty spaces within the gas.
2. Constant Random Motion: Gas particles are in continuous, rapid, and random motion, moving in straight lines until they collide with other particles or the walls of the container.
3. Negligible Intermolecular Forces: The attractive forces between gas particles are very weak. This lack of strong attraction means the particles do not tend to stay together and are not bound to any specific positions.
Due to these characteristics, when a gas is placed in a container, its particles will move randomly in all directions, exploring all available space. Since the forces holding the particles together are negligible and the particles themselves are far apart, they will spread out until they occupy the entire volume of the container, thus filling it completely.
Question:
For any substance, why does the temperature remain constant during the change of state?
Concept in a Minute:
During a change of state (like melting or boiling), the energy absorbed or released is used to break or form intermolecular bonds, not to increase the kinetic energy of the particles. The kinetic energy of particles is directly proportional to temperature. Therefore, while the phase is changing, the temperature remains constant.
Explanation:
When a substance changes state, for example, from solid to liquid (melting) or from liquid to gas (boiling), the heat energy that is supplied does not increase the kinetic energy of the molecules. Instead, this energy is used to overcome the intermolecular forces of attraction between the particles. In melting, the energy is used to break the bonds holding the particles in a fixed, rigid structure. In boiling, the energy is used to overcome the attractive forces between molecules in the liquid state, allowing them to escape as a gas. This absorbed energy is called latent heat. Since the kinetic energy of the molecules (which determines temperature) does not change, the temperature of the substance remains constant until the entire substance has undergone the change of state. Similarly, during condensation or freezing, energy is released as latent heat as new intermolecular bonds are formed, but this release doesn’t cause a temperature drop until the state change is complete.
Question:
Give reasons:
A wooden table should be called a solid.
Concept in a Minute:
The question requires understanding the defining characteristics of a solid substance in chemistry and physics. Key properties to consider include fixed shape, fixed volume, incompressibility, and the arrangement of particles.
Explanation:
A wooden table should be called a solid because it exhibits the characteristic properties of a solid state of matter.
1. Fixed Shape: A wooden table maintains its shape irrespective of the container it is in. You can move it from one room to another, but its form doesn’t change.
2. Fixed Volume: The space occupied by the wooden table remains constant. It does not expand or contract significantly to fill its surroundings.
3. Rigidity/Incompressibility: Solids are generally rigid and difficult to compress. A wooden table is very hard to press into a smaller volume.
4. Definite Boundaries: A solid has clear and definite boundaries. The edges of the table define its extent.
5. Intermolecular Forces: In solids, the particles (molecules or atoms) are held together by strong intermolecular forces, which keeps them in fixed positions, leading to the rigidity and fixed shape. The wood in the table is composed of molecules that are tightly packed and vibrate about their fixed positions.
Question:
What is the physical state of water at 0°C.
Concept in a Minute:
Phase transitions of water, specifically melting point and freezing point. Water exists in solid (ice), liquid (water), and gaseous (steam) states depending on temperature and pressure. The melting point of ice and the freezing point of water are key temperatures where phase changes occur.
Explanation:
At 0°C, water can exist in two physical states: solid (ice) and liquid (water). This is because 0°C is the melting point of ice and the freezing point of water at standard atmospheric pressure. At this specific temperature, water molecules have enough energy to overcome the rigid structure of ice, allowing them to move more freely as a liquid, but also have enough that they can arrange themselves into the crystalline structure of ice. Therefore, at 0°C, both phases, solid and liquid, can coexist in equilibrium. If heat is added, the ice will melt into liquid water. If heat is removed, liquid water will freeze into ice. Without further information about whether heat is being added or removed, or the initial state of the water, we can say that water at 0°C can be either solid, liquid, or a mixture of both.
Question:
Convert the following temperature to the celsius scale.
470 K
Concept in a Minute:
The Kelvin scale and Celsius scale are two different units of temperature measurement. The Kelvin scale is an absolute temperature scale, meaning its zero point is absolute zero, the theoretical lowest possible temperature. The Celsius scale is a relative temperature scale, with its zero point defined as the freezing point of water at standard atmospheric pressure. The relationship between Kelvin and Celsius is a direct conversion.
Explanation:
To convert a temperature from the Kelvin scale to the Celsius scale, we use the following formula:
Celsius (°C) = Kelvin (K) – 273.15
In this question, the given temperature is 470 K.
Using the formula:
Celsius (°C) = 470 – 273.15
Celsius (°C) = 196.85
Therefore, 470 K is equal to 196.85 °C.
Often, for simplicity in high school problems, the conversion factor 273 is used instead of 273.15. If we use 273:
Celsius (°C) = 470 – 273
Celsius (°C) = 197
Both answers are generally accepted depending on the precision required. For NCERT high school, using 273 is usually sufficient.
Final Answer: 196.85 °C (or 197 °C if using 273 as the conversion factor)
Question:
Arrange the following substances in increasing order of forces of attraction between particles –
water, sugar, oxygen
Concept in a Minute:
The forces of attraction between particles determine the state of matter and how easily particles can move. Stronger forces of attraction mean particles are held more closely and move less freely. Solids have the strongest forces, liquids have weaker forces than solids but stronger than gases, and gases have the weakest forces.
Explanation:
We need to compare the forces of attraction between the particles of water, sugar, and oxygen.
Water is a liquid. In liquids, the forces of attraction between particles are moderate. Particles can slide past each other but are still relatively close.
Sugar is a solid. In solids, the forces of attraction between particles are very strong. Particles are held in fixed positions and vibrate.
Oxygen is a gas. In gases, the forces of attraction between particles are very weak. Particles are far apart and move randomly at high speeds.
Therefore, the increasing order of forces of attraction between particles is:
Oxygen (weakest forces) < Water (moderate forces) < Sugar (strongest forces)
The final answer is $\boxed{\text{oxygen, water, sugar}}$.
Question:
Why does a desert cooler cool better on a hot dry day?
Concept in a Minute:
Evaporation is the process by which a liquid changes into a gas. This process requires energy, which is absorbed from the surroundings, leading to a cooling effect. The rate of evaporation depends on factors like temperature, humidity, and air movement.
Explanation:
A desert cooler works on the principle of evaporative cooling. When water evaporates from the porous pads of the cooler, it absorbs heat from the surrounding air. This absorption of heat causes the air temperature to decrease. On a hot day, the ambient temperature is high, providing a significant temperature difference that drives faster evaporation. On a dry day, the humidity is low, meaning the air can hold more water vapor. This low humidity also facilitates a higher rate of evaporation. Therefore, on a hot dry day, both factors – high temperature and low humidity – contribute to a significantly higher rate of evaporation from the cooler’s pads. As a result, more heat is absorbed from the air, leading to a more pronounced cooling effect, and the desert cooler cools better.
Question:
How does water kept in an earthen pot (matka) become cool during summer?
Concept in a Minute:
Evaporation, heat transfer, latent heat of vaporization
Explanation:
An earthen pot (matka) has small pores on its surface. When water is stored in the pot, some of this water seeps out through these tiny pores. During the summer, the ambient temperature is high, which provides enough heat energy for the water that has seeped out to evaporate. Evaporation is a process where liquid water changes into water vapor. This change of state requires energy, which is absorbed from the surrounding water in the pot and the pot itself. This absorbed heat energy is known as the latent heat of vaporization. As the water molecules absorb heat and turn into vapor, they carry this heat away from the pot and its contents. Consequently, the remaining water inside the earthen pot loses heat and its temperature decreases, making it feel cool. This continuous process of seepage and evaporation helps maintain a significantly lower temperature of the water inside the matka compared to the surroundings.
Question:
Liquids generally have lower density as compared to solids. But you must have observed that ice floats on water. Find out why.
Concept in a Minute:
Density is defined as mass per unit volume. The state of a substance (solid, liquid, gas) affects its molecular arrangement and thus its density. For most substances, the solid form is denser than the liquid form. However, water is an exception due to its unique molecular structure and hydrogen bonding.
Explanation:
Water molecules are polar, meaning they have a slight positive charge on the hydrogen atoms and a slight negative charge on the oxygen atom. In liquid water, these molecules are relatively close together, but they can move past each other. When water freezes into ice, the molecules arrange themselves into a crystalline lattice structure. This structure is held together by hydrogen bonds, which create more space between the molecules compared to their arrangement in liquid water. Because the molecules in ice are farther apart, a given volume of ice contains less mass than the same volume of liquid water. Therefore, ice has a lower density than water, and it floats.
Question:
Give reasons:
We can easily move our hand in air, but to do the same through a solid block of wood, we need a karate expert.
Concept in a Minute:
The question relates to the concept of resistance to motion, which is determined by the medium through which an object moves. This resistance is largely due to the forces between the particles of the medium. In solids, these forces are strong, making them resistant to penetration. In gases (like air), these forces are weak, offering little resistance.
Explanation:
In air, the particles are far apart and exert very weak forces on each other. This means there’s very little opposition when you move your hand through it. You can easily push the air particles aside. However, a solid block of wood is made of particles that are very tightly packed and held together by strong intermolecular forces. To move your hand through it, you would need to overcome these strong forces, which requires a significant amount of energy and force. A karate expert can generate enough concentrated force to break the bonds between the wood particles, allowing them to move their hand through the wood.
Question:
What produces more severe burns, boiling water or steam?
Concept in a Minute:
The concept involved is the transfer of heat energy. When a substance changes state (like water to steam), it absorbs or releases a significant amount of energy called latent heat. This latent heat, in addition to the sensible heat (temperature-related heat), plays a crucial role in the severity of burns.
Explanation:
Steam produces more severe burns than boiling water. Boiling water is at 100°C. When steam comes into contact with skin, it first condenses into boiling water at 100°C. During this condensation process, steam releases a large amount of latent heat of vaporization to the skin, in addition to the heat already present due to its temperature. Boiling water, on the other hand, only transfers its sensible heat (heat due to its temperature) to the skin. Therefore, the total heat transferred by steam to the skin is much greater than that transferred by boiling water at the same temperature, leading to more severe burns.
Question:
What is the physical state of water at 100ºC?
Concept in a Minute:
The physical state of a substance depends on its temperature and pressure. Water has three common physical states: solid (ice), liquid (water), and gas (steam). The transition points between these states are called boiling point (liquid to gas) and freezing point (solid to liquid). At standard atmospheric pressure, water freezes at 0ºC and boils at 100ºC.
Explanation:
At 100ºC, water is at its boiling point under standard atmospheric pressure. This means that at this temperature, liquid water absorbs enough heat energy to overcome the intermolecular forces holding the water molecules together in a liquid state. As a result, the water molecules gain enough kinetic energy to escape into the gaseous phase, forming steam. Therefore, at 100ºC, water exists as a gas. If the pressure were different from standard atmospheric pressure, the boiling point would also change, but assuming standard conditions, the answer is gas.
Question:
Give reasons for the following observation:
The smell of hot sizzling food reaches you several metres away, but to get the smell from cold food you have to go close.
Concept in a Minute:
Diffusion: The movement of particles from a region of higher concentration to a region of lower concentration. Temperature affects the rate of diffusion. Higher temperature leads to faster movement of particles.
Explanation:
The smell of food is due to the presence of volatile molecules released by the food. These molecules spread through the air via diffusion. When food is hot, the molecules have more kinetic energy and move faster. This increased speed leads to a much higher rate of diffusion. As a result, the volatile molecules from hot food spread quickly and widely through the air, allowing you to smell them from several metres away. When the food is cold, the molecules have less kinetic energy and move much slower. The rate of diffusion is significantly reduced, so the volatile molecules do not travel as far or as quickly. Therefore, you need to be close to the cold food to detect its smell.
Question:
Give a reason for the following observation.
Naphthalene balls disappear with time without leaving any solid.
Concept in a Minute:
The key concept is sublimation. Sublimation is the process where a solid directly changes into a gas without passing through the liquid state. Factors affecting sublimation rate include temperature and surface area.
Explanation:
Naphthalene is a solid substance that readily undergoes sublimation. This means that at room temperature, the naphthalene molecules gain enough energy to escape directly from the solid state into the gaseous state, forming naphthalene vapor. This process occurs gradually over time. Since the naphthalene turns into a gas and disperses into the air, no solid residue is left behind, explaining why the naphthalene balls disappear without leaving any solid. The rate of sublimation is influenced by the temperature; at higher temperatures, sublimation occurs faster. The larger the surface area of the naphthalene balls exposed to the air, the faster they will sublimate.
Question:
Give a reason for the following observation.
We can get the smell of perfume sitting several metres away.
Concept in a Minute:
Diffusion: The movement of particles from a region of higher concentration to a region of lower concentration. In the case of gases, this movement is often random and driven by the kinetic energy of the molecules.
Explanation:
Perfume is a liquid that easily evaporates to form a gas. When the perfume evaporates, its molecules spread out into the air. This spreading out is due to diffusion. The perfume molecules are initially highly concentrated near the source (the perfume bottle). As they move into the surrounding air, where their concentration is much lower, they naturally spread out to fill the available space. This random movement of perfume molecules continues until they are evenly distributed throughout the air. Because the air is a fluid and the perfume molecules are constantly in motion, they can travel several metres, allowing you to smell the perfume from a distance.
Question:
Why does our palm feel cold when we put some acetone or petrol or perfume on it?
Concept in a Minute:
The key concept is evaporation and its cooling effect. Evaporation is the process where a liquid turns into a gas. This process requires energy, which is absorbed from the surroundings. When a volatile liquid evaporates from our palm, it absorbs heat from our palm, making it feel cold.
Explanation:
Acetone, petrol, and perfume are volatile liquids. This means they have a high vapor pressure and evaporate easily at room temperature. When you put a small amount of these liquids on your palm, they start to evaporate. Evaporation is an endothermic process, meaning it absorbs heat from its surroundings. In this case, the surroundings are your palm. As the liquid absorbs heat from your palm to change into vapor, your palm loses heat, and consequently, it feels cold. The faster the rate of evaporation, the more heat is absorbed, and the colder your palm will feel.
Question:
Give reasons:
A gas exerts pressure on the walls of the container.
Concept in a Minute:
Kinetic Theory of Gases: Gases are composed of a large number of tiny particles (atoms or molecules) that are in constant, random motion. These particles collide with each other and with the walls of the container.
Explanation:
A gas exerts pressure on the walls of its container because its constituent particles are in continuous, random motion. These particles collide with the walls of the container. Each collision exerts a small force on the wall. Since there are a vast number of particles in the gas, the cumulative effect of these countless collisions results in a continuous force exerted on the walls per unit area, which is what we define as pressure. The faster the particles move (higher temperature) and the more particles there are in a given volume (higher density), the more frequent and forceful these collisions will be, leading to higher pressure.
Question:
Convert the following temperature to Celsius scale:
573 K
Concept in a Minute:
The relationship between Kelvin and Celsius temperature scales is a linear conversion. The Kelvin scale is an absolute temperature scale where 0 K represents absolute zero, the theoretical lowest possible temperature. The Celsius scale is a relative scale where 0°C represents the freezing point of water at standard atmospheric pressure. To convert from Kelvin to Celsius, subtract 273.15 from the Kelvin temperature.
Explanation:
The question asks to convert a temperature from the Kelvin scale to the Celsius scale.
The formula for converting Kelvin (K) to Celsius (°C) is:
°C = K – 273.15
Given temperature in Kelvin = 573 K.
To convert this to Celsius, we apply the formula:
°C = 573 – 273.15
Performing the subtraction:
573.00
– 273.15
——-
299.85
Therefore, 573 K is equal to 299.85°C.
Final Answer: The final answer is $\boxed{299.85}$
Question:
What is the physical state of water at 25°C.
Concept in a Minute:
States of Matter: Water exists in three states: solid (ice), liquid (water), and gas (steam/water vapor). The state depends on temperature and pressure.
Phase Transitions: Changes in temperature cause phase transitions between these states.
Melting Point: The temperature at which a solid changes into a liquid (0°C for water at standard pressure).
Boiling Point: The temperature at which a liquid changes into a gas (100°C for water at standard pressure).
Explanation:
Water’s normal melting point (solid to liquid) is 0°C, and its normal boiling point (liquid to gas) is 100°C at standard atmospheric pressure.
The question asks about the physical state of water at 25°C.
Since 25°C is above the melting point (0°C) and below the boiling point (100°C), water at this temperature exists in its liquid state.
Question:
Convert the following temperature to the Kelvin scale.
25°C
Concept in a Minute:
The Kelvin scale is an absolute temperature scale where 0 Kelvin represents absolute zero, the theoretical point at which all molecular motion ceases. The Celsius and Kelvin scales are related by a simple linear conversion formula.
Explanation:
To convert a temperature from Celsius (°C) to Kelvin (K), we use the formula:
K = °C + 273.15
In this question, the temperature is given as 25°C.
Applying the formula:
K = 25 + 273.15
K = 298.15
Therefore, 25°C is equal to 298.15 K.
Detailed Steps:
1. Identify the given temperature in Celsius: 25°C.
2. Recall the conversion formula from Celsius to Kelvin: K = °C + 273.15.
3. Substitute the given Celsius temperature into the formula.
4. Perform the addition to calculate the temperature in Kelvin.
5. State the final answer with the correct unit.
Question:
A diver is able to cut through water in a swimming pool. Which property of matter does this observation show?
Concept in a Minute:
This question relates to the properties of matter, specifically focusing on the behavior of liquids. The key concept here is the fluidity of liquids and their ability to be easily deformed.
Explanation:
A diver is able to cut through water because water is a liquid. Liquids have a property called fluidity, which means they can flow and change shape easily. This is because the particles in a liquid are not held in fixed positions like in a solid, but are able to move past each other. When a diver moves through water, their body displaces the water molecules, and because the water is fluid, it easily moves aside to allow the diver to pass. This demonstrates the fluidity of water, a characteristic property of liquids.
Question:
What is the physical state of water at 250°C.
Concept in a Minute:
The physical state of water (solid, liquid, or gas) depends on its temperature and pressure. The key temperatures to consider for water are its melting point (0°C) and boiling point (100°C) at standard atmospheric pressure.
Explanation:
At standard atmospheric pressure, water exists as:
– Solid (ice) below 0°C.
– Liquid between 0°C and 100°C.
– Gas (steam or water vapor) above 100°C.
The question asks about the physical state of water at 250°C. Since 250°C is significantly above the boiling point of water (100°C) at standard atmospheric pressure, water will be in its gaseous state. Therefore, at 250°C, water exists as steam or water vapor.
Question:
What are the characteristics of particles of matter?
Concept in a Minute:
The question asks about the fundamental properties that describe the tiny building blocks of all matter. To answer this, you need to recall the basic characteristics that define the particles of solids, liquids, and gases. These characteristics relate to their size, movement, and how they interact with each other.
Explanation:
The particles of matter possess the following characteristics:
1. They are very, very small.
2. They are in constant motion.
3. They have intermolecular spaces between them.
4. They have intermolecular forces of attraction between them.
Question:
Convert the following temperature to the Kelvin scale.
373°C
Concept in a Minute:
The relationship between Celsius and Kelvin temperature scales is linear. To convert from Celsius to Kelvin, add 273.15 to the Celsius temperature. The formula is K = °C + 273.15.
Explanation:
The question asks to convert a temperature from Celsius to the Kelvin scale.
The given temperature is 373°C.
The formula to convert Celsius to Kelvin is:
Kelvin (K) = Celsius (°C) + 273.15
Substitute the given Celsius temperature into the formula:
K = 373 + 273.15
K = 646.15
Therefore, 373°C is equal to 646.15 K.
Final Answer: The final answer is $\boxed{646.15 K}$
Question:
Convert the following temperature to Celsius scale:
300 K
Concept in a Minute:
The relationship between Kelvin (K) and Celsius (C) temperature scales. The formula to convert Kelvin to Celsius is C = K – 273.15.
Explanation:
The question asks to convert a temperature from the Kelvin scale to the Celsius scale. The given temperature is 300 K. The formula to convert Kelvin to Celsius is:
Celsius (°C) = Kelvin (K) – 273.15
Substitute the given Kelvin temperature into the formula:
°C = 300 – 273.15
°C = 26.85
Therefore, 300 K is equal to 26.85 °C.
Final Answer: The final answer is $\boxed{26.85 \ ^\circ C}$
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