Internal energy and energy transfers (3.2) (M)

Question 1

How is energy stored inside a system? What is this called?

Answer 1

Stored by the particles (atoms and molecules) that make up the system.

This is called internal energy

Question 2

What is internal energy?

Answer 2

The total kinetic energy and potential energy of all the particles (atoms and molecules) that make up a system

internal energy = kinetic energy + potential energy

Question 3

How does heating change the energy stored within the system?

Answer 3

By increasing the energy of the particles that make up the system.

This either raises the temperature of the system or produces a change of state

Question 4

What is another way other than heating, to raise the internal temperature?

Answer 4

By stretching the object (increases elastic potential store)

Question 5

3 needed

If the temperature of the system increases, the increase in temperature depends on what?

Answer 5

• the mass of the substance heated
• the type of material
• the energy input to the system

Question 6

What does a low specific heating capacity mean?

Answer 6

The substance doesn’t need much energy to heat it (can change state more easily)

Question 7

What is latent heat?

Answer 7

The energy needed for a substance to change state

Question 8

What happens to the energy supplied when a substance changes state?

Answer 8

the energy supplied changes the energy stored (internal energy) but not the temperature

Question 9

What is the specific latent heat of a substance?

Answer 9

The amount of energy required to change the state of 1kg of the substance with no change in temperature

Question 10

What does specific latent heat of fusion apply to?

Answer 10

change of state from solid to liquid

Question 11

What does the specific latent heat of vaporisation?

Answer 11

change of state from liquid to vapour

Question 12

What does a heating curve look like?

Answer 12

Question 13

What does a cooling curve look like?

Answer 13

ignore supercooling

Question 14

How does heat pass through a substance (eg window)?

Answer 14

atoms gain kinetic energy (due to increased temp) and transfer this energy to neighbouring atoms

Question 15

4 marker - key

Explain in terms of particles, how evaporation causes the cooling of water

Answer 15

the fastest particles have enough energy

to escape from the surface of the water

therefore the mean energy of the remaining particles decreases

the lower the mean energy of particles the lower the temperature (of the water)

Question 16

4 marks

Why does a mirror get misty when someone uses a shower?

Answer 16

water evaporates

water particles rise in air

mirror (surface) cooler than air

(so water particles) condense

Question 17

Why will convection/conduction not take place in a vacuum?

Answer 17

convection/conduction require a medium

Question 18

How would an air gap between two walls reduce heat loss?

Answer 18

Air is a poor conductor so reduces heat transfer by conduction

Question 19

3 marks

How is heat lost through a double glazed window?

Answer 19

heat is conducted through glass

passes through glass and air by radiation

crosses air gap by convection

due to 2nd point could be removed?

Question 20

3 marks

How is a convection current created in water in a saucepan?

Answer 20

As heat is transferred through the saucepan, water particles at the bottom move faster

water becomes less dense or water expands

Warm water rises or colder water falls to take its place