Flashcards · 9702 · A Level Topic 14

Temperature (A Level) flashcards

16 cards on A Level Topic 14, subtopics 14.1 to 14.3. Pick a subtopic or study them all.

Study mode needs JavaScript. Every card is listed below, so you can still cover the answers and test yourself.

All 16 cards

For a quick read-through or printing. Cover the right-hand side to test yourself.

In which direction is thermal energy transferred?: From a region of higher temperature to a region of lower temperature, not from higher to lower internal energy.
Thermal equilibrium: Two bodies are in thermal equilibrium when there is no net transfer of thermal energy between them. This happens when they are at the same temperature.
Why does a thermometer read the temperature of the body it touches?: Once thermal equilibrium is reached there is no net energy flow, so the thermometer is at the same temperature as the body.
Are temperature and thermal energy the same thing?: No. A large bath of warm water can hold far more thermal energy than a cup of boiling water, yet energy flows from the cup to the bath if they are in contact.

Physical properties that vary with temperature and can be used to measure it: For example: the density of a liquid, the volume of a gas at constant pressure, the resistance of a metal, the e.m.f. of a thermocouple.
What is special about the thermodynamic (Kelvin) scale?: It is an absolute scale that does not depend on the property of any particular substance. Two empirical thermometers can agree at the fixed points yet disagree between them.
Absolute zero, 0 K: The temperature at which all substances have minimum internal energy.
Converting between kelvin and degrees Celsius: T/K = θ/°C + 273.15.
Is a temperature change of 15 °C the same as a change of 15 K?: Yes. Intervals are the same size on both scales; only absolute temperatures differ (by 273.15). T must still be in kelvin in pV = nRT.
Triple point of water, 273.16 K: The unique temperature and pressure at which ice, water and water vapour coexist in equilibrium.

Specific heat capacity: The energy needed per unit mass to raise the temperature by one degree (1 K), without a change of state. Q = mcΔθ. Unit J kg⁻¹ K⁻¹.
How much energy heats 500 g of water (c = 4200 J kg⁻¹ K⁻¹) from 20 °C to 80 °C?: Q = mcΔθ = 0.500 × 4200 × 60 = 126 000 J.
Specific latent heat: The energy needed per unit mass to change the state of a substance without a change of temperature. Q = mL. Unit J kg⁻¹.
Specific latent heat of fusion vs of vaporisation: Fusion: solid ↔ liquid (melting or freezing). Vaporisation: liquid ↔ gas (boiling or condensing).
Why is the specific latent heat of vaporisation larger than that of fusion?: Boiling must separate the molecules completely, overcoming the intermolecular forces, and also do work pushing back the atmosphere. Melting only loosens the forces.
Why is the temperature constant on a heating or cooling curve during a change of state?: The energy transferred changes the potential energy of the molecules (latent heat), not their mean kinetic energy.