Heat and Temperature

Question 1

What does it mean if a variable is intensive/extensive?

Answer 1

Intensive - independent of the scale of the system.

Extensive - scales with the system

Question 2

What is a open/closed system?

Answer 2

Open - can exchange energy and mass with its surroundings

Closed - can exchange only energy with its surroundings

Question 3

What are adiabatic/diathermal walls?

Answer 3

Adiabatic - prevent heat transfer.

Diathermal - all heat transfer.

Question 4

What does isothermal mean?

Answer 4

At constant temperature.

Question 5

What does isochoric mean?

Answer 5

Constant volume.

Question 6

What does isobaric mean?

Answer 6

Constant pressure.

Question 7

What does adiabatic mean?

Answer 7

No heat flow or a sudden process (before heat flow can occur).

Question 8

What is Le Chatelier’s Principle?

Answer 8

A system in equilibrium reacts to a small change in one of its variables by changing its internal conditions to reverse the change. (stay in equilibrium)

Question 9

What is the definition of thermal equilibrium?

Answer 9

Two systems are in thermal equilibrium if their state variables do not change when they are put in contact via a diathermal wall.

Question 10

State the 0th Law of Thermodynamics.

Answer 10

Two systems are in thermal equilibrium if, and only if, they have the same temperature.

Question 11

What is the internal energy of a system?

Answer 11

The sum of the translational, vibrational and rotational energies of it’s components.

Question 12

How do you know if something is a thermometer?

Answer 12

If it has an observable property which changes with temperature.

Question 13

What is the ice point?

Answer 13

Liquid and solid water in thermal equilibrium at 1 atmosphere. (0 degrees C)

Question 14

What is the steam point?

Answer 14

Liquid and vapour water at thermal equilibrium at 1 atmosphere (100 degrees C)

Question 15

How do gas thermometers work?

Answer 15

They use one reference point - absolute zero - 273 degrees C or 0K.

Question 16

What is the equation for linear thermal expansion?

Answer 16

α = 1/L0 * ΔL/ΔT, where L0 is the value of the dimension at some initial T0.

Question 17

How would you calculate length using the equation for linear thermal expansion?

Answer 17

L = L0 + ΔL = L0 + αL0ΔT

Question 18

What does the graph look like for potential energy between two atoms bound in a solid?

Answer 18

Goes from positive to negative and then tends to zero (u shape). Higher temp = wider curve.

Question 19

What is the equation for volume thermal expansion?

Answer 19

β = 1/V0 * ΔV/ΔT = 3α (since dV = 3L^2 dL)

Question 20

What are the 2 equations for ΔT in terms of heat flow Q?

Answer 20

ΔT = Q/nC, where C is the molar heat capacity and n is the number of mole
OR
ΔT = Q/mCm, where Cm is the specific heat capacity

Question 21

What is the specific heat capacity of water?

Answer 21

4190 J K^-1 kg^-1

Question 22

What is meant by latent heat?

Answer 22

Latent heat is the amount of heat involved in a phase change.

Question 23

What is the equation for heat transfer Q?

Answer 23

Q = +/- m*L, where L is the latent heat.

Question 24

How do you draw a phase diagram for p-T? What is the centre point called?

Answer 24

Like a diagonal Y shape with curvey lines - solid on left, vapour at bottom and liquid at top. Centre called triple point.

Question 25

On the p-T diagram, what is the line between solid and vapour called?

Answer 25

Sublination curve.

Question 26

What happens at the critical point?

Answer 26

Separation between liquids and vapour ends - beyond there is a smooth continuous change.

Question 27

What is the equation for heat flow in conduction?

Answer 27

dQ/dt = -κA dT/dx, where κ is the thermal conductivity (-ve sign because heat flows from higher to lower temperature.

Question 28

What can cause convection?

Answer 28

Local changes of density or temperature which causes heat flow due to motion of fluid.

Question 29

What is the equation for power in radiation?

Answer 29

P = eσA*T^4 (Stefan - Bolzmann Law), where e is the emissivity and σ is the Stefan-Boltzmann constant.