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Question
Answer the following:
a. What is meant by latent heat? How will the state of matter transform if latent heat is given off?
b Which principle is used to measure the specific heat capacity of a substance?
c. Explain the role of latent heat in the change of state of a substances?
d. On what basis and how will you determine whether air is saturated with vapour or not?
a. What is meant by latent heat? How will the state of matter transform if latent heat is given off?
b Which principle is used to measure the specific heat capacity of a substance?
c. Explain the role of latent heat in the change of state of a substances?
d. On what basis and how will you determine whether air is saturated with vapour or not?
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Solution
a. Latent heat of a body is the amount of heat required to change the state of unit mass of the body from solid to liquid or from liquid to gas without any change in temperature. If latent heat is given off, then the body in liquid state will transform to solid state and the body in vapour state will transform to liquid state. This means the internal energy of the matter decreases when latent heat is given off.
b. Principle of heat exchange is used in the calorimetry method to determine the specific heat capacity of a substance.
c. According to the kinetic model, the total energy of a molecule is the sum of kinetic energy due to its motion (which depends on temperature) and its potential energy (which depends on the force of attraction between the molecules and the separation between them. During the phase change of a substance, its temperature does not increase and hence its kinetic energy. But the potential energy increases or decreases depending on the type of phase transformation (for ex: while melting of ice, the separation between the molecules of ice increases and hence its potential energy). Thus, some energy is required in increases or decreasing the separation between the molecules. Thus, the heat supplied during phase transformation is used up in increasing or decreasing the potential energy and this heat energy is known as latent heat.
d. On the basis of amount of water vapours present in the air, it can be either saturated or unsaturated. If the amount of water vapours exceeds the amount that the air can contain, then it is called saturated. If the amount of water vapour is less than the limit of the amount that air can contain then it is called unsaturated.
We can determine whether the air is saturated with vapour or not in terms of relative humidity. If the relative humidity is 100%, the air will be saturated otherwise not.
b. Principle of heat exchange is used in the calorimetry method to determine the specific heat capacity of a substance.
c. According to the kinetic model, the total energy of a molecule is the sum of kinetic energy due to its motion (which depends on temperature) and its potential energy (which depends on the force of attraction between the molecules and the separation between them. During the phase change of a substance, its temperature does not increase and hence its kinetic energy. But the potential energy increases or decreases depending on the type of phase transformation (for ex: while melting of ice, the separation between the molecules of ice increases and hence its potential energy). Thus, some energy is required in increases or decreasing the separation between the molecules. Thus, the heat supplied during phase transformation is used up in increasing or decreasing the potential energy and this heat energy is known as latent heat.
d. On the basis of amount of water vapours present in the air, it can be either saturated or unsaturated. If the amount of water vapours exceeds the amount that the air can contain, then it is called saturated. If the amount of water vapour is less than the limit of the amount that air can contain then it is called unsaturated.
We can determine whether the air is saturated with vapour or not in terms of relative humidity. If the relative humidity is 100%, the air will be saturated otherwise not.
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