P1.1/2/3 - Heat

Question 1

What does temperature tell us?

Answer 1

The temperature of an object tells us how hot is it and is measured in degrees Celsius. It does not tell us how much heat it contains.

Question 2

What is heat?

Answer 2

Heat is a form of energy and is measured in Joules (J).

Question 3

The hotter something is the more heat energy it has. How is energy lost for example in a hot drink?

Answer 3

Energy is continuously transferred to into surroundings until the temperature of the drink is the same as its surroundings.

Question 4

The difference in temperature between and object and its surroundings affects the rate at which energy is transferred. When the temperature difference is greater, the rate of energy transfer is ______.

Answer 4

Higher

Question 5

What happens in terms of energy transfer when an object is cooler than its surroundings?

Answer 5

The object gains energy from its surroundings and warms up.

Question 6

What is a thermogram?

Answer 6

A thermogram can be used to show how hot an object is. A picture is taken using a special camera and different temperatures are shown by different colours. White is the hottest and then cooler in descending order red, yellow, green, light blue and dark blue (coolest).

Question 7

What is temperature a measure of?

Answer 7

Temperature is a measure of the average kinetic energy of particles in a substance. The temperature scale (degrees Celsius) was creating with reference points such as freezing and boiling points. At 0 degrees Celsius the particles in ice are still vibrating. They stop vibrating at - 273.16 degrees Celsius.

Question 8

What is heat a measure of?

Answer 8

Heat is a measure on energy on an absolute scale. It has no reference points. Is it measured in Joules.

Question 9

When an object is getting hotter it is (i)______ energy. When an object cools down it is (ii)______ energy.

Answer 9

(i) gaining

(ii) losing

Question 10

Different materials will hold a different amount of energy. What is specific heat capacity?

Answer 10

The specific heat capacity of a material is defined as the amount of energy is joules(J) needed to raise the temperature of 1kg of the material by 1 degree Celsius. Its units are joules per kilogram per degree Celsius (J/kg°C)

Question 11

It takes more energy to raise the temperature of 1kg of water than it does to raise the temperature of 1kg of aluminium. We can say that water has a _____ specific heat capacity.

Answer 11

higher

Question 12

What is the specific heat capacity of water?

Answer 12

4200 J/kg°C

Question 13

What calculation can you use to work out the amount of energy required to heat and object?

Answer 13

Energy = mass x specific heat capacity x temperature change

J = kg x J/kg°C x °C

e.g a kettle has 1.5 kg of water at a temperature of 18 °C, how much energy is needed to bring it to boil?

J = 1.5(mass) x 4200J/kg°C (SHC of water) x [100°C-18°C] (temperature change)
Answer: 516 600 J

Question 14

Why is water used in central heating systems to transfer thermal energy from the boiler to the radiators?

Answer 14

It is used in central heating systems because it has a very high specific heat capacity. It can store a much larger amount of thermal energy than other liquids. This also means that the water does not need to be pumped around the system very quickly.

Question 15

How can you work out the specific heat capacity of something?

Answer 15

You can only do this if you know the amount of heat transferred, the mass of the object and the temperature rise. Then rearrange the equation to make specific heat capacity the subject:
Energy = mass x specific heat capacity x temperature change
OR
J = kg x J/kg°C x °C

Question 16

Give two examples of changes of state

Answer 16

• Ice melting into water (Solid to liquid)

- Liquid turning to gas

Question 17

While something is changing state the temperature remains (i)______. If you then continue adding or removing energy/heat from the substance the temperate continues to (ii) ________ at a steady rate.

Answer 17

(i) constant

(ii) rise/fall

Question 18

What needs to happen for something to change state?

Answer 18

There needs to be an increase or decrease in energy. This depends on how the state is changing.
E.g

• Solid to liquid = increase in energy
• Liquid to solid = decrease in energy

Question 19

What is specific latent heat?

Answer 19

The amount of energy (in joules) needed to change the state of 1kg of a substance. You can calculate the amount of energy needed :
energy = specific latent heat x mass
J = J/kg x kg

Question 20

What unit is used to measure specific latent heat?

Answer 20

The unit is joules per kilogram (J/kg). Often the energy is measured in kilojoules (1 kJ= 1000J). Then specific latent heat is given in the unit kilojoules per kilogram (kJ/kg)

Question 21

The specific latent heat of fusion (melting a substance) is not the same value as the specific latent heat of vaporistation (boiling and evaporating a substance.)

Answer 21

……………

Question 22

What is latent heat of fusion (melting a substance)?

Answer 22

The latent heat of fusion is the energy needed to break the intermolecular bonds between the particles in the solid so that they can move around. When a liquid boils and evaporates, energy is used to break the bonds between the particles in the liquid to change their state into a gas.

Question 23

Why does the temperature of a substance not change when intermolecular bonds are broken, even though energy is needed?

Answer 23

Temperature does not change when a substance is changing state.