Thermal

Question 1

Define internal energy.

Answer 1

The sum of kinetic and potential energy of all particles in a substance. Only one of these can change at a time.

Question 2

How can you combine SLH and SHC to find the change in temperature of a drink with ice?

Answer 2

Energy gained by ice = energy lost by drink
mL (ice) + mc(T-T1) (water) = mc(T2-T) (drink)

Question 3

How do you convert from Celsius to kelvin?

Answer 3

Add 273

Question 4

How can you find absolute zero without actually cooling a substance to it?

Answer 4

Plot a graph of pressure or volume against temperature (in degrees Celsius) and extrapolate to the x intercept (algebraically).

Question 5

State Boyle’s law.

Answer 5

Pressure is inversely proportional to volume (at constant temperature).

Question 6

State Charles’s Law.

Answer 6

Volume is directly proportional to temperature (at constant pressure).

Question 7

State the pressure law.

Answer 7

Pressure is directly proportional to temperature (at constant volume).

Question 8

What is the difference between n and N?

Answer 8

n - moles
N - number of molecules

Question 9

State the five assumptions made for the kinetic theory of gases. (Hint: RAVED)

Answer 9

• Random: particles move randomly (Brownian motion).
• Attraction: no attractive forces between particles.
• Volume: volume of particles is negligible compared to that of gas.
• Elastic: all collisions are elastic.
• Duration: the duration of collisions is negligible compared to the time between them.

Question 10

Derive the kinetic theory equation (using particle in cubic metre).

Answer 10

• Rate of change of momentum = 2mu
• Time taken = 2l/u
• Force = rate of change of momentum = 2mu/(2l/u) = mu²/l
• Pressure = force/area = mu²/l³ = mu²/V
• u_rms² = 1/3 c_rms³
• PV = 1/3 Nmc²