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A change of state of matter occurs when a substance changes from one state to another. Solids, liquids, and gases are the three common states of matter.
- The change in state from solid to liquid, as well as from liquid to vapor/gas, is accommodated by two common changes of state.
- When a substance absorbs a particular amount of energy, its atoms and molecules move rapidly, increasing its kinetic energy. This increase in kinetic energy helps to push the particles apart, causing the substance to change phase.
- Melting is the conversion of a substance from a solid to a liquid state.
- Vaporization is the process of conversion of a substance from its liquid phase to its gaseous (vapor) phase.
- The triple point of a substance is the temperature and pressure at which its three phases coexist in thermodynamic equilibrium. It is the point at which the sublimation, fusion, and vaporization curves intersect.
Very Short Answers Questions [1 Mark Questions]
Ques. What is regelation?
- Refreezing of ice on reduction in pressure
- Melting of ice at a higher temperature than its melting point
- Refreezing of ice on addition of impurities
- Melting of ice at a lower temperature than its melting point due to an increase in pressure
Ans. The correct answer is a. Refreezing of ice on reduction in pressure
Explanation: When there is an increase in pressure, water melts. When the excess pressure is removed, it may refreeze. This refreezing is known as relegation.
Ques. What happens to the boiling point of water in a container when the container is completely closed by a lid?
- Remains same
- Decreases
- Increases
- The boiling point is characteristic of a substance
Ans. The correct answer is c. Increases
Explanation: When the vapor pressure of a liquid equals the air pressure, boiling occurs. The vapor pressure rises as the temperature increases. When the temperature increases sufficiently, boiling begins. However, when pressure increases, higher vapor pressure must be reached, which is obtained by increasing temperature, and therefore the point of boiling increases.
Ques. Condensation temperature is the same as evaporation temperature.
- True
- False
Ans. The correct answer is a. True
Explanation: Condensation is the process of converting vapor to liquid, whereas evaporation is the process of converting liquid to vapor. The only difference between the two is that heat is removed in the former and added in the latter.
Ques. Select the correct statement
- Change of phase occurs at variable temperature
- The boiling point increases with an increase in pressure
- On heating continuously a substance changes from solid to gas via the liquid phase only
- Water can exist in all 3 phases
Ans. The correct answer is d. Water can exist in all 3 phases
Explanation: Water can exist in all three phases that are thermally equilibrium with one another. It is known as the triple point of water. When a material is heated, it can go from solid to gas. This is known as sublimation. The boiling point rises as pressure decreases. At constant pressure, phase change occurs.
Ques. Getting burnt by steam is less dangerous than boiling water.
- True
- False
Ans. The correct answer is b. False
Explanation: Water must be boiled before it can be converted into steam by adding more heat energy. As a result, steam is more dangerous than boiling water.
Ques. Change of phase occurs at a constant temperature, which implies that even with the addition of heat to a substance temperature remains constant.
- True
- False
Ans. The correct answer is a. True
Explanation: Heat provided during the phase change is used to change intermolecular distances while the temperature remains constant.
Short Answers Questions [2 Marks Questions]
Ques. What are the factors that affect the changing state of matter?
Ans. The factors that affect the state of matter change are
- Variation in temperature
- Variation in pressure
- Change in intermolecular force of attraction
- Change in the kinetic energy of the particles
Ques. What is the reason for the occurrence of phase changes?
Ans. When the temperature or pressure of a system varies, changes in phase occur. The interaction between molecules increases as the temperature or pressure rises. Similarly, when the temperature decreases, it becomes easier for molecules and atoms to form a more solid structure.
Ques. What are the two basic types of changes that occur in the matter?
Ans. Matter undergoes two types of changes: chemical change and physical change.
The natural characteristic of matter remains unchanged during the process of physical change, irrespective of changes in its state, size, and shape. And, in the case of chemical change, there is no way to reverse it; it can only be done under very specific circumstances.
Ques. Why is solid CO2 termed as dry ice?
Ans. When the pressure decreases to 1 atm, solid CO2 transforms directly into a gaseous state without becoming liquid, which is why it is also known as dry ice. As a result, it is stored under high pressure.
Ques. Why do water vapors at 100 ℃ cause more burns as compared to liquid water at the same temperature?
Ans. At 100 ℃, water vapors have more energy than similar liquid particles. This occurs because, as compared to water in liquid form, water vapors absorb more energy in the form of latent heat of vaporization.
Ques. What is the Latent heat of vaporization?
Ans. The amount of heat required to transform a unit mass of liquid into a gaseous phase under constant temperature circumstances is referred to as latent heat of vaporization."
The conversion of liquid particles into water vapors is an example of a process using latent heat of vaporization.
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Long Answers Questions [3 Marks Questions]
Ques. Explain the effect of pressure on changing states of matter.
Ans. The effect of pressure on changing states of matter:
- The distance between the particles that make up a material determines its state of matter.
- Thus, when pressure is given to a gas, it compresses to a liquid, and when pressure is applied to a liquid, it solidifies.
- Pressure has little effect on solids.
- When a material is subjected to pressure, its condition changes from gas to liquid to solid.
Ques. How many basic changes of states of matter are there?
Ans. Basically, there are six changing states of matter, and they are as follows:
- Melting: Melting is the process in which a substance in a solid state changes into a liquid state.
- Freezing: Freezing is the process in which a substance in a liquid state is converted into a solid state.
- Vaporization: It is the process in which a change of state occurs from liquid to gas.
- Condensation: During this process, the state of matter changes from gas to liquid.
- Sublimation: It is the process in which substances in a solid state are directly converted into the gaseous state.
- Deposition: It is the process in which substances in a gaseous form are directly converted into a solid state.
Ques. Define intermolecular space. Describe it in terms of distinct states of matter.
Ans. Intermolecular space is the space between the atoms/molecules of matter. Intermolecular spaces between solid particles are small, but intermolecular spaces between gases are large.
- Molecules of the solid are tightly packed and only oscillate around their mean positions due to strong intermolecular interactions. Between solids, there is no intermolecular space.
- Because of weak intermolecular interactions, the molecules in a liquid are packed densely together. These forces are less than those of solids but greater than those of gases. Liquids have a fixed volume and may easily take on the form of a vessel. Although the intermolecular gap is small, it is essential.
- Gas particles are separated by a larger distance. The particles are free to move about since the force of attraction between them is weak. The volume or shape of a gas does not characterize it. Intermolecular space is abundant and free-flowing.
Very Long Answers Questions [5 Marks Questions]
Ques. How does matter change from one state to another?
Ans. Heat, cold, or other processes can cause a change in the state of matter.
- When something is heated, the intermolecular distance between molecules expands and the intermolecular force in solids and liquids decreases, changing the state of the object from solid to liquid or gas.
- While intermolecular force between molecules decreases as a result of cooling, intermolecular space increases.
The substance changes from one state to another in the following ways:
- On melting, it changes from a solid state to a liquid state.
- On boiling, substances convert from a liquid state into a gaseous state.
- On sublimation, substances change from a gaseous state to a solid state.
- On freezing, substances convert from a liquid state into a solid state.
- On condensation, substances change state from gas to liquid.
Ques. What is the difference between boiling and evaporation?
Ans. The following are the differences between boiling and evaporation
| Boiling | Evaporation |
|---|---|
| Boiling is an unnatural process in which the liquid is continuously heated up to a point where it vaporizes. | Evaporation is the process that takes place when a liquid is converted into a gas due to a rise in temperature and pressure. |
| Boiling normally happens on the whole mass of the heated liquid. | Evaporation normally happens on the surface of a hot liquid. |
| The bubbling effect is observed during the boiling process. | The bubbling effect is not observed during the boiling process. |
| The boiling process is substantially faster. | Evaporation is a slow process. |
Ques. What is the effect of temperature on the inter-conversion of states of matter?
Ans. The effect of temperature in the inter-conversion of states of matter
- One of the main causes of a change in the state of matter is temperature.
- The kinetic energy of the constituent particles of the solid rises when it is heated. As a result, the particles begin to vibrate faster. This additional energy helps the particles overcome the inter-particle forces of attraction.
- They soon leave their positions and begin to move more freely. As a result, the material melts and changes into a liquid.
- Temperature remains constant until all solids are converted into liquids. The given heat is used to convert a solid into a liquid by overcoming the inter-particle attraction force.
- As a result, the solid substance absorbs heat energy without increasing in temperature. Similarly, when a liquid material is heated, the kinetic energy of its constituent particles rises, causing the particles to vibrate faster.
- This extra energy helps the particles overcome the inter-particle attraction forces. They soon begin to move more freely. As a result, the liquid state changes into the gaseous state.
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