Lesson 4: Specific latent heat + graphs

Question 1

What is the specific latent heat?

Answer 1

• Specific latent heat is the energy needed for a 1kg of a substance to change state, with no temperature change.

no temp change: just break forces of attraction not increase temp

Question 2

What is the specific latent heat of fusion?

Answer 2

• Energy required to change 1kg of a substance from solid to liquid with no change in temp.

Question 3

What is specific latent heat of vaporisation?

Answer 3

• Energy required to change 1kg of substance from liquid to vapour, with no change in temp.

Question 4

What is the equation for specific latent heat?

Answer 4

E = mL
E= energy
m = mass
L = latent heat

Question 5

What part of the curve of heating graph should we look at for SHC?
1.) Flat
2.) Increasing temp

Answer 5

• Increasing temp

Question 6

What part of the curve of heating graph should we look at for SLH?
1.) Flat
2.) Increasing temp

Answer 6

• Flat
• Change of state occuring
• No change in temp.

Question 7

What is the unit for specific latent heat?

Answer 7

• J/ Kg

Question 8

Q.)

Calculate energy transfer to surroundings when 0.4kg of
substance changed state from solid to liquid.
Specific latent heat of fusion = 199000J/Kg.

Answer 8

• E = mL
• 0.4 x 199000 = 79600J

Question 9

Q.)

Why does the temperature continue to decrease after a solid has changed to a liquid? (2)

Answer 9

• Liquid has higher temp than surroundings.
• Needs to reach same temp as surroundings.

Question 10

Q.)

Why does temp of water in kettle not increase straight away when water is put in?

Answer 10

• It takes time for heating element to heat up.

Question 11

Q.)

If you remove a thermometer from a liquid each time you are measuring temp change, what type of error is this.

Answer 11

• Random error

Question 12

Q.)

What is a random error?

Answer 12

• When readings are spread out from true value.
• Results vary in unpredictable way from one measure to next.

Question 13

Q.)

How can the temperature increasing part of the a graph showing heating in a kettle show the power output of the kettle?

Answer 13

• Gradient = change in temp/time.
• Power x time = change in tempx mass x specific heat capacity
• P = gradient x mc.

Question 14

SPEC

If a system is heated, what is the increase in temperature dependent on?

Answer 14

• Mass of substance
• Type of material
• Energy input into the system