14: Exam Questions

Question 1

Explain how the energy of a water molecule in steam changes with time (at a constant temp.)

Answer 1

(frequent) collisions with other particles 2) energy transfer at each collision 3) energy change at each collision is random 4) average energy of a particle (over time) is constant

Question 2

Explain why some gas passing through a hot tube will ionise

Answer 2

1) atoms exchange energy on each collision; 2) high temperature means atoms have high energy / collision rate; 3) some atoms gain enough energy to be ionised;

Question 3

Random walk. A typical molecule in air is displaced by 5 mm in 1 s. Explain why it will take 100s to be displaced by 50mm

Answer 3

Distance (proportional) √N. N (proportional) t, so D (proportional) √t. 5/√1 = 50/√100

Question 4

The first law of thermodynamics can be written in the form ΔU =Q – W
Sate the meaning of each term.
(2)

Answer 4

ΔU – change / increase in internal energy
Q – Heat supplied to the gas /system
W – Work done by the gas / system

Question 5

More air is pumped into the tank and the pressure rises. The temperature of the air does not change. Explain why adding more air increases the pressure. (2)

Answer 5

More frequent collisions (between air particles and walls of container)
Greater rate of change of momentum