Change of State

Question 1

When a liquid is heated at its boiling point:

Answer 1

• The particles gain more energy
• Move further apart still
• The liquid becomes a gas
• The potential energy of the particles is increased.

Question 2

What is the melting point?

Answer 2

The temperature at which a pure substance melts.

Question 3

What is the latent heat of fusion.

Answer 3

The energy needed to change the state of a solid to a liquid without change of temperature.

Question 4

As a gas cools and condenses:

Answer 4

• latent heat energy is released
• the bonds pull the particles together
• a liquid is formed.

Question 5

What is latent heat of vaporisation?

Answer 5

The energy needed to change the state of a liquid to a vapour without change of temperature.

Question 6

What is sublimation?

Answer 6

The change of state when a solid changes to a vapour directly.

Question 7

What is specific latent heat of vaporisation?

Answer 7

The amount of energy needed to change of unit mass of the substance from a liquid to a vapour without a change in temperature.

Question 8

Heat supplied Q =

Answer 8

ml

Question 9

Specific latent heat of vaporisation of water=

Answer 9

2.25 MJ kg⁻¹

Question 10

Assumptions made when doing latent heat calculations:

Answer 10

• No change in temp
• All heat used to change the state of the substance (none lost to surroundings)
• Rate of energy transfer is constant.

Question 11

What is fusion?

Answer 11

A word to describe the metling of a solid because the solid fuses into a liquid?

Question 12

Latent means hidden.

Answer 12

Latent heat supplied to melt a solid is hidden because no temperature change takes place even though the solid is being heated.

Question 14

When heat energy is supplied to a substance:

Answer 14

• Its temperature gradually rises as shown on the graph but with no temperature rise at the melting and boiling points.
• The energy is absorbed as:
  
  • specific heat when the temp rises causing the molecules to have more kinetic energy and vibrate faster either as a solid or a liquid
  • latent heat as the substance melts or vaporises causing the molecules to have more potential energy as they move apart from each other

Question 15

When a substance cools it gives out:

Answer 15

• Latent heat energy as it changes from a gas to a liquid and as it solidifies
• Specific heat energy as it drops in temperature.