Thermal T1-T5 Flashcards
define specific heat capacity
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.
What is the internal energy of an object?
The sum of the random distribution of kinetic and potential energies.
What is the equation of the specific heat capaity?
Q = m x c x change in temperature
What is the equation of the specific heat of vaporisation/fusion?
Q = m x l
What is the other energy equation that helps containing time?
Q = P x time
Q = time x current x p.d.
A change in the internal energy can result from what?
Heat being transferred in to or out of the system Q.
Work being done on or by the system.
What is the equation containing energy, internal energy and work done?
Q = U (delta) + W
What is the kinetic energy related to in the internal energy?
Temperature and therefore the mean molecular KE.
What is the potential energy related to in the internal energy?
State and therefore the mean molecular PE.
What are the similarities and differences between the Celsius and kelvin temperature scales?
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.
Define ‘specific latent heat of fusion’.
The energy required to change the state of 1kg of a substance, without a change in temperature.
Solid to liquid, or vice versa.
Define ‘specific latent heat of vaporisation’.
The energy required to change the state of 1kg of a substance, without a change in temperature.
Liquid to gas, or vice versa.
When is energy released?
When mass condenses or freezes.
So when the substance becomes colder.
What type of energy doesn’t change when a substance is melting or vaporising?
Temperature.
What type of energy doesn’t change when the temperature is changing?
The state or kinetic energy.
What change in state or temperature takes the most energy and therefore time?
Liquid to Gas.
State the energy changes involved when putting ice cubes into a warm drink.
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)
How can we use a graph of temperature against time to calculate SHC?
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.
How can we use a graph of temperature against time to calculate SLH?
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).
‘Continuous flow calorimeter’:
(i) Describe how this can be used to find SHC of a fluid.
- Liquid is passed through the apparatus at a constant flow rate. Temp is measured before and after.
- 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.
- the flow rate of the liquid is changed and step 2 is repeated for the same change in temp.
- Formula => Q heater + Q water = H
Q heater = (m x c x change in temp) + H. - Find power other both b the heater.
- power2 - power 1 = rate of flow of the liquid x c x change in temp.
‘Continuous flow calorimeter’:
(ii) How can we deal with the heat loss in this method?
By the conservation of energy and mass as the change in temp is the same.
What is the equation used to measure the specific heat capacity of a liquid by mixing?
mctemp (cold) + mctemp (copper) + mctemp (hot) = 0
Sketch a graph of temperature against time for heating ice until it becomes water vapour.
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.
Suggest why the specific latent heat of vaporisation of water is much greater than the specific latent heat of fusion of water.
Greater change in PE in vaporisation then melting.
Vaporisation, work is done against atmospheric pressure.
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).
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.
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
Q = m x c x delta temp
(8.5 x 10^3) / (4200 x 0.12) = 17K
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.
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)
