Specific Latent Heat

Question 1

what happens to the provided energy when a substance reaches its boiling or melting point

Answer 1

• it changes from being transferred to the kinetic energy stores to the particles
• to being used to weaken or break the intermolecular bonds between the particles

Question 2

what happens when a substance condenses or freezes

Answer 2

bonds are forming between the particles which releases energy

Question 3

what does it mean in, terms of the temperature of a substance, if bonds are formed between particles, which releases energy

Answer 3

it means that the temperature doesnt go down until all of the all of the substance had turned into a liquid (condensing) or solid (freezing)

Question 4

what is the step by step practical which explores the changing temperatures in relation to changes of state

Answer 4

• fill a beaker with crushed ice
• place a thermometer into the beaker and record the temp of the ice
• using a bunsen burner, heat the beaker full of ice
• every 20 seconds, record the temp and the current state of the ice
• continue the process until the water beings to boil
• plot a graph of temp against time

Question 5

what should a temperature against time graph of melting ice and boiling water look like

Answer 5

• the temperature should linearly increase
• until it plateaus for a certain period of time
• then the temp should steadily rise again
• until it hits another plateau and stays horizontal for a certain period of time
• then the temp should continue to steadily increase

Question 6

what is happening in the first plateau in the temp time graph

Answer 6

• the solid ice is changing state into liquid water by melting
• the line indicates ice’s melting point

Question 7

what is happening in the second plateau in the temp time graph

Answer 7

• the liquid water is changing state into a the gas steam by evaporating
• the line indicates water’s boiling point

Question 8

what do flat lines on a temp time graph always show

Answer 8

the changing of state

Question 9

what is the specific latent heat of a change of state of a substance

Answer 9

it is the amount of energy required to change 1kg of the substance from one state to another without changing its temperature

Question 10

what is the specific latent heat for cooling

Answer 10

the energy released by a change of state

Question 11

what is the specific latent heat for heating

Answer 11

the energy absorbed or inputted for a change of state

Question 12

what are the two things that specific latent heat is different for

Answer 12

• it is different for different types of materials

- and the changing between different states of the same material

Question 13

what is the specific latent heat of fusion

Answer 13

the specific latent heat for changing between a solid and a liquid (melting and freezing)

Question 14

what is the specific latent heat of vaporisation

Answer 14

the specific latent heat for changing between a liquid and a gas (evaporating, boiling or condensing)

Question 15

what formula do you use to work out the energy needed or released when a substance of mass changes state

Answer 15

• thermal energy = mass x specific latent heat

- Q = m * L

Question 16

what are the units for thermal energy, mass and specific latent heat and which one is at the top of triangle

Answer 16

• unit for thermal energy is J
• unit for mass is kg
• unit for specific latent heat is J/kg

Question 17

what is the difference between specific heat capacity and specific latent heat

Answer 17

• specific heat capacity is the amount of energy needed to raise the temp of 1kg of a substance by 1C
• whereas the specific latent heat is the amount of energy needed to change the state of 1kg of a substance from one to another