Thermal Energy Transfer COPY

Question 1

Define Internal energy

Answer 1

The sum of the randomly distributed kinetic and potential energies of the particles in a body.

Question 2

Where does the electric potential energy that particles have come from?

Answer 2

The electrostatic forces that the particles exert on each other.

Question 3

What is the first law of thermodynamics?

Answer 3

Heat supplied to a system = work done by system + increase in internal energy.

Heat supplied = (pressure x change in volume) + increase in internal energy

Question 4

When will the work done by the system be positive?

Answer 4

If the material does work e.g. when a gas expands and pushes back the atmosphere

Question 5

When will the work done by the system be negative?

Answer 5

If the gas contracts as then work is done on the gas.

Question 6

When is the heat supplied to a system negative?

Answer 6

If heat energy leaves the substance

Question 7

Define specific heat capacity

Answer 7

The heat energy required to raise 1kg of a substance through 1^oC.

Question 8

What are the units of specific heat capacity?

Answer 8

J/Kg/^oC

Question 9

What is the specific heat capacity equation?

Answer 9

Q = mc∆ø

Question 10

How do you calculate heat gain/loss per second?

Answer 10

mass x SHC x temperature rise/loss per second

Question 11

Why will the SHC of water that has been calculated from an experiment be too high? (3)

Answer 11

• Some heat will be lost to the atmosphere
• Some heat energy will be lost to the insulation and the thermometer
• Some heat energy will be lost due to the evaporation of the water and so will not cause the temp of the water to rise

Question 12

What type of errors are heat losses?

Answer 12

Systematic

Question 13

Why are heat energy losses systematic errors?

Answer 13

All the errors will cause the measured value for the increase in temperature to be too low

Question 14

How can errors from heat losses be reduced? (3)

Answer 14

• Increasing the insulation of the calorimeter
• Use a thermometer with a thermal heat capacity which will not absorb the heat energy
• Start the experiment 5^oC below RT and finishing 5^oC above so that helf the time the water will absorb heat from the surroundings and half the time the water will release heat to the surroundings.

Question 15

Define specific latent heat of fusion

Answer 15

The heat energy required to turn unit mass from solid to liquid at constant temperature

Question 16

What are the units for specific latent heat of fusion?

Answer 16

J/Kg

Question 17

What is the equation for specific latent heat of fusion?

Answer 17

Q = mL_f

Question 18

Define specific latent heat of vapourisation

Answer 18

The heat energy required to turn unit mass from liquid to gas at constant temperature

Question 19

What are the units of Latent heat of vapourisation?

Answer 19

J/Kg

Question 20

What is the equation for specific latent heat of vapourisation?

Answer 20

Q = mL_v

Question 21

Why doesn’t the temperature change when something changes state?

Answer 21

• The substance either loses/gains heat energy
• The Ek of the particles stays the same so the temperature doesn’t change
• The potential energy decreases (bonds form) or increases (bonds break)

Question 22

Draw the cooling curve for stearic acid

Answer 22

Question 23

What is the method to measure the SHC of water?

Answer 23

Question 24

What is the theory behind the practical to measure the SHC of water?

Answer 24

• Assume no heat is lost from the calorimeter
• Energy supplied = energy supplied to calorimeter + energy supplied to water
• VIt = m_calC_cu(ø₂-ø₁) + m_wC_w(ø₂-ø₁)

Question 25

What is the method for measuring the temperature of a Bunsen flame?

Answer 25

• Measure the mass of the weight/nail/nut
• Measure the mass of the calorimeter
• Fill the tin can with 50 cm³ of water. Measure the new mass of the calorimeter to finf the exact mass of water
• Measure initial temp of water
• Heat the brass weight until it is red hot
• Drop the weight into the water and stir with a glass rod
• Measure the max temperature the water reaches

Question 26

What is the theory behind the measuring the temerature of the bunsen flame practical.

Answer 26

• Energy lost by the brass weight when it enters the water and drops in temperature = energy gained by water from the nail which increases its temperature