Change of State

Question 1

What is latent heat?

Answer 1

Latent heat is the amount of heat required to change the state of a substance without changing its temperature. For example, the heat required to convert ice into water at 0°C without any temperature change is latent heat.

Question 2

What is specific latent heat?

Answer 2

Specific latent heat is the amount of heat required to change the state of a unit mass of a substance without a change in temperature. It is specific to the substance and the type of phase change.

Question 3

What is specific latent heat of fusion?

Answer 3

Specific latent heat of fusion is the amount of heat required to convert a unit mass of a solid into a liquid at its melting point without a change in temperature.

Question 4

What is specific latent heat of vaporization?

Answer 4

Specific latent heat of vaporization is the amount of heat required to convert a unit mass of a liquid into a gas at its boiling point without a change in temperature.

Question 5

What is the difference between melting, evaporation, and boiling?

Answer 5

• Melting: The process of changing from a solid to a liquid at a specific temperature (melting point).
• Evaporation: The process of changing from a liquid to a gas at any temperature below the boiling point. It occurs at the surface of the liquid.
• Boiling: The process of changing from a liquid to a gas at the boiling point, where the entire liquid is involved in the phase change.

Question 6

How does pressure influence boiling and melting points?

Answer 6

Increasing pressure raises the boiling point and lowers the melting point of most substances. Decreasing pressure lowers the boiling point and raises the melting point. For example, water boils at a lower temperature at higher altitudes where atmospheric pressure is lower.

Question 7

How do dissolved substances affect boiling and melting points?

Answer 7

Dissolved substances, like salt in water, elevate the boiling point (boiling point elevation) and lower the melting point (freezing point depression) of the solvent.

Question 8

How can you differentiate between latent heat and specific latent heats of fusion and vaporization?

Answer 8

Latent heat is the total heat required for a phase change, while specific latent heat is the heat required per unit mass. Specific latent heat of fusion applies to solid-liquid transitions, and specific latent heat of vaporization applies to liquid-gas transitions.

Question 9

How can you solve numerical problems related to latent heat?

Answer 9

Use the formula
𝑄 = 𝑚 × 𝐿
where 𝑄 is the heat required,
𝑚 is the mass, and
𝐿 is the specific latent heat (either of fusion or vaporization), and apply given values to solve for the unknowns.