14: Exam Questions Flashcards

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1
Q

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

A

(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

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2
Q

Explain why some gas passing through a hot tube will ionise

A

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;

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3
Q

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

A

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

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4
Q

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

A

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

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5
Q

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)

A

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

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