Question

Water cools from 2°C to −2°C. During this time, what happens to the motion of the molecules?

a
The motion of the molecules remains the same.
b
The motion of the molecules stops.
c
The motion of the molecules increases.
d
The motion of the molecules decreases.

Answer 1

d

As temperature falls the average kinetic energy of the molecules drops, so their motion decreases. At 0°C water freezes, so translational motion is greatly reduced (molecules become bound in a lattice and only vibrate).