Thermodynamics

Question 1

Heating

Answer 1

Energy transferred by conduction or convection or radiation. Driven by temperature difference.

Question 2

Conduction

Answer 2

by lattice-vibration in solids + also electron diffusion in metals (it is a random process driven by the transfer of KE due to collisions - but results in a net flow from hot to cold)

Question 3

Convection

Answer 3

by rise of less-dense (hotter) material (in a fluid - e.g. gas or liquid)

Question 4

Radiation

Answer 4

by emission of electromagnetic radiation from atoms

Question 5

Internal energy

Answer 5

Sum of KE (in molecular vibration) + PE (in molecular bonds). Any change of state or change in temperature means Internal Energy has changed

Question 6

Specific Heat Capacity (c)

Answer 6

“The energy required to raise the temperature of 1 kg of a material by 1K, without a change of state.”
ΔE = mcΔΘ (units = J kg-1 K-1)

Question 7

Specific Latent Heat of fusion (L)

Answer 7

“the energy per unit mass to change a solid into a liquid, without a change in temperature.”
ΔE = LΔm (units = Jkg-1)

Question 8

Specific Latent Heat of vaporisation (L)

Answer 8

“the energy per unit mass to change a liquid into a gas, without a change in temperature.”
ΔE = LΔm (units = Jkg-1)

Question 9

Working

Answer 9

By doing work against a force ΔW = FΔs (increase in internal energy by mechanical work done on the molecules.)(independent of temperature difference)

Question 10

Electrical work

Answer 10

ΔW = VIΔt (increase in internal energy by electrical work done on the molecules.) (independent of temperature difference)

Question 11

Pressure

Answer 11

p = F/A
Force/Area applied
(Units = Nm-2 or Pa.)

Question 12

Reasons for increase in pressure of gas

Answer 12

The speed of the particles increases causing more energetic collisions with the container
The rate of collisions increases because they take less time to travel across the container.

Question 13

Evidence for the assumpution that: Gas particles move with rapid, random motion

Answer 13

Brownian motion

Question 14

Evidence for the assumpution that: All collisions are elastic (No energy is lost at the collisions.)

Answer 14

Particles do not slow down or settle in their containers

Question 15

Evidence for the assumpution that: Forces between gas particles are negligible (in between the collisions).

Answer 15

Distances between particles is large (in coparison to to
particle size)

Question 16

Evidence for the assumpution that: The volume of each gas particle is negligible (compared to the volume of gas as a whole).

Answer 16

Gases can be compressed by a large factor

Question 17

Internal energy

Answer 17

For ‘real’ gases this is made up of molecular KE and PE. (PE is stored up in the molecular bonds).
In ‘ideal’ gases there is no PE.

Question 18

Equation applied to a fixed gas

Answer 18

(p1V1)/T1 = (p2V2)/T2

Question 19

Ideal Gas Equation

Answer 19

pV = NkT
N = Number of molecules
k = Boltzmann constant (1.38 x 10-23 J K-1)

Question 20

Average kinetic energy of single molecule

Answer 20

½ m<c2> = 3/2kT</c2>

Question 21

Derevation formula

Answer 21

p = (1/3)ρ<c2>4
ρ = density of gas (kgm-3).</c2>