Heat energy

Question 1

What is the symbol for heat energy

Answer 1

Q

Question 2

What is heat energy?

Answer 2

Heat energy is the total energy of all the movement of the particles in a substance.

Question 3

What does heat energy depend on?

Answer 3

• the speed of the particles
• the number of particles
• the type of particles in the substance

Question 4

What is heat energy measured in?

Answer 4

J

Question 5

What is temperature?

Answer 5

Moving particles have kinetic energy. The temperature of a substance is the average kinetic energy of all the particles in that substance. As it is an average, the number of particles and the size of the container the substance is in do not affect the temperature.

Question 6

How is heat energy different from temperature?

Answer 6

If a 1L container of water is 100°C and a 500ml container of water is also 100°C, the temperature is the same however the 1L has more heat energy because it has a greater number of particles with the same temperature and therefore the total energy is more.

Question 7

Temperature is a measure of energy

Answer 7

But not energy

Question 8

What is temperature measured in?

Answer 8

Degrees (°C)

Question 9

What is absolute zero?

Answer 9

The temperature at which all particle motion stops

-273°C

Question 10

What is the specific heat capacity symbol?

Answer 10

c

Question 11

What is specific heat capacity?

Answer 11

How much energy is needed to raise the temperature of one kilogram of a substance by one degree Celsius

Question 12

What is the heat energy equation?

Answer 12

Q = mcΔT

where Q is the amount of heat energy absorbed OR released in J
m = kg
c in Jkg(-1)°C(-1)
ΔT in °C

Question 13

What happens when heat energy is added or removed from a substance? (3)

Answer 13

• Volume changes: when substances gain heat energy they usually expand because their particles vibrate more quickly and occupy more space. When they lose heat energy they usually contract
• Temperature changes: when substances absorb heat energy usually their temperature increases, whereas a substance that loses energy will usually have a temperature decrease.
• State (phase) changes: if solids absorb sufficient heat energy, they change into liquid or gas. Liquids change into solids if they lose enough heat energy.

Question 14

Phase changes terms

Answer 14

Solid to gas: sublimation

Gas to solid: deposition

Question 15

What must be needed for a phase change?

Answer 15

Heat energy must be either added or removed. When heat energy is added to a state of matter, its particles vibrate more (solids) or move faster (liquids and gases). The faster the particles vibrate/move, the further the particles move apart and the weaker the forces between them becomes, resulting in a change of state.

Question 16

What are the two places where temperature stays the same when heat is being added

Answer 16

when a phase change is occurring.

The temp stays the same when the ice melts into water.
The temp stays the same while water boils into steam

Question 17

What is latent heat

Answer 17

the heat energy of the flat sections of the heating curve. The temp does not change as heat E supplied is being used to overcome the attractive forces between the particles so that they move further apart and the sate changes.

Question 18

Why do melting and freezing occur at the same temperature?

Answer 18

During freezing, heat energy is removed. During melting, heat energy is being absorbed.

Question 19

What is latent heat

Answer 19

The latent heat of a substance is the amount of heat energy absorbed or released when one kilogram of a substance changes state while the temp remains constant.

Question 20

What are the two types of latent heat?

Answer 20

Latent heat of fusion - the heat energy required to change a solid to liquid
Latent heat of vaporisation - the heat energy required to change a liquid to gas

Question 21

What is latent heat measured in

Answer 21

J Kg^-1

Question 22

What is the formula for latent heat

Answer 22

Q = mL

Q = heat energy absorbed or released in J
m= kg
K = latent heat of vaporisation or fusion, in JKg^-1

Question 23

Equation for total amount of E involved in a temp change where there is a phase change

Answer 23

Q(total) = Q(latent) + Q(specific)

Question 24

Which substance has a really high latent heat of fusion value?

Answer 24

Water. 340000Jkg-1

Question 25

How do chilly bins work

Answer 25

When food or drinks are stored in a chilly bin with ice, the heat E required to melt the ice comes from the food or drinks - this leaves the food or drinks at a lower temp, as heat E has been removed from them to heat the ice and change the ice into water.

Question 26

How does water help prevent frost damage?

Answer 26

Heat energy is released by water when it freezes. If frost is predicted, farmers will turn on sprinklers. As the water falls on the plants it will begin to freeze, causing heat E to be released into the surroundings and plants (such as grape vines and stone fruit). This heat E helps to keep the plants warm enough so they are not damaged by frosts. However, this method only works when the air temp does not fall far below freezing.

Question 27

Which substance has one of the highest latent heat of vaporisation?

Answer 27

Water. 22 600 005 J needed to evaporate 1kg of water.

Question 28

Why do we feel cold when we are wet?

Answer 28

When you come out of the shower or the pool, heat E from your body causes the water on your body to vaporise. As a result of losing heat energy from your body, you feel cold.

Question 29

Why does steam burn

Answer 29

When steam condenses to liquid water, it releases heat E into its surroundings. When just 1mL steam condenses into water, it releases 2260J of heat E. If this condensed water then has to cool from 100°C to body temp (37°C), even more heat energy will be released. For this reason, a steam burn at 100°C is far worse than a burn from the same volume of boiling water at 100°C.

Question 30

What is power

Answer 30

when a substance changes temp, heat E is either absorbed or released. The rate at which this occurs is the POWER.

Question 31

Power equation

Answer 31

P = E/t

P in W
E in J
t in s

1W = 1Js-1