Thermal T1-T5

Question 1

define specific heat capacity

Answer 1

Of a substance is the energy needed to raise the temperature of 1kg of the substance by 1 degrees Celsius without a change in state.

Question 2

What is the internal energy of an object?

Answer 2

The sum of the random distribution of kinetic and potential energies.

Question 3

What is the equation of the specific heat capaity?

Answer 3

Q = m x c x change in temperature

Question 4

What is the equation of the specific heat of vaporisation/fusion?

Answer 4

Q = m x l

Question 5

What is the other energy equation that helps containing time?

Answer 5

Q = P x time
Q = time x current x p.d.

Question 6

A change in the internal energy can result from what?

Answer 6

Heat being transferred in to or out of the system Q.
Work being done on or by the system.

Question 7

What is the equation containing energy, internal energy and work done?

Answer 7

Q = U (delta) + W

Question 8

What is the kinetic energy related to in the internal energy?

Answer 8

Temperature and therefore the mean molecular KE.

Question 9

What is the potential energy related to in the internal energy?

Answer 9

State and therefore the mean molecular PE.

Question 10

What are the similarities and differences between the Celsius and kelvin temperature scales?

Answer 10

1 change in temperature in degrees celsius is the same as the value in kelvin.
0K = absolute zero = -273 degrees celsius.
0 degrees celsius = 273K.

Question 11

Define ‘specific latent heat of fusion’.

Answer 11

The energy required to change the state of 1kg of a substance, without a change in temperature.
Solid to liquid, or vice versa.

Question 12

Define ‘specific latent heat of vaporisation’.

Answer 12

The energy required to change the state of 1kg of a substance, without a change in temperature.
Liquid to gas, or vice versa.

Question 13

When is energy released?

Answer 13

When mass condenses or freezes.
So when the substance becomes colder.

Question 14

What type of energy doesn’t change when a substance is melting or vaporising?

Answer 14

Temperature.

Question 15

What type of energy doesn’t change when the temperature is changing?

Answer 15

The state or kinetic energy.

Question 16

What change in state or temperature takes the most energy and therefore time?

Answer 16

Liquid to Gas.

Question 17

State the energy changes involved when putting ice cubes into a warm drink.

Answer 17

Ice to water so.. Q = ml (fusion)
Water to common temperature Q = mc x change in temperature (rise)
Water to common temperature Q = mc x change in temperature (decrease)
Cup to common temperature Q = mc x change in temperature (decrease)

Question 18

How can we use a graph of temperature against time to calculate SHC?

Answer 18

Take the gradient of the graph which is the change of temperature over the time. As power = Q/t. Therefore power = mc x (delta temp / time). Therefore you can find the specific heat capacity from a temperature against time graph.

Question 19

How can we use a graph of temperature against time to calculate SLH?

Answer 19

Use the horizontal part of the curve/line on the graph in order to calculate the time needed for the total energy transferred with the E = Pt, and us the formula, E = ml(vaporisation/fusion).

Question 20

‘Continuous flow calorimeter’:
(i) Describe how this can be used to find SHC of a fluid.

Answer 20

1. Liquid is passed through the apparatus at a constant flow rate. Temp is measured before and after.
2. The p.d. across the heater is adjusted so that the change in temp of the liquid flowing through the apparatus is a suitable value. The current through the heaters also measured.
3. the flow rate of the liquid is changed and step 2 is repeated for the same change in temp.
4. Formula => Q heater + Q water = H
   Q heater = (m x c x change in temp) + H.
5. Find power other both b the heater.
6. power2 - power 1 = rate of flow of the liquid x c x change in temp.

Question 21

‘Continuous flow calorimeter’:
(ii) How can we deal with the heat loss in this method?

Answer 21

By the conservation of energy and mass as the change in temp is the same.

Question 22

What is the equation used to measure the specific heat capacity of a liquid by mixing?

Answer 22

mctemp (cold) + mctemp (copper) + mctemp (hot) = 0

Question 23

Sketch a graph of temperature against time for heating ice until it becomes water vapour.

Answer 23

The graph looks like a series of steps.
Up, level, up, longer level, up again.
1st up = liquid.
1st level = fusion.
2nd up = liquid.
2nd level = vaporisation.
3rd up = gas.

Question 24

Suggest why the specific latent heat of vaporisation of water is much greater than the specific latent heat of fusion of water.

Answer 24

Greater change in PE in vaporisation then melting.
Vaporisation, work is done against atmospheric pressure.

Question 25

Explain why there is likely to be a greater mass of water in the cup than you have calculated? (Energy of water to temp rise + Energy of gas to liquid = 0).

Answer 25

Energy from the steam is needed to raise temperature of the cup.
or
Energy/heat will be lost to the surroundings/cup/the driver the heating.

Question 26

An electrical immersion heater supplies 8.5kK of energy every second. Water flows through the heater at a rate of 0.12 kg s^-1.

Assuming all the energy is transferred to the water, calculate the rise in temperature of the heater as it flows through the heater.

SHC of water = 4200 J kg^-1 K^-1

Answer 26

Q = m x c x delta temp

(8.5 x 10^3) / (4200 x 0.12) = 17K

Question 27

An electrical immersion heater supplies 8.5kK of energy every second. Water flows through the heater at a rate of 0.12 kg s^-1.

The water suddenly stops flowing at the instant when its average temperature is 26 degrees Celsius. The mass of the water trapped in the heater is 0.41 kg. calculate the time taken for the water to reach 100 degrees Celsius if the immersion heater continues supplying energy at the same rate.

Answer 27

P = (m / t) x c x delta temp

Therefore t = (m / P) x c x delta temp

t = (0.41 x 4200 x (100-26)) / (8.5 x 10^3)