Which of the graphs below might represent a mixture of pure water and ice exposed to a room temperature of 3°C?

four bar charts

A. Graph A

B. Graph B

C. Graph C

D. Graph D

C. Graph C  

Explanation:

We have a mixture of water and ice.

At 0 °C they are at equilibrium.

water-to-ice rate = ice-to-water rate

Next, we lower the temperature to -3 °C — just slightly below freezing.

The water will slowly turn to ice.  

The water-to-ice rate will be slightly faster than the ice-to-water rate.

The purple bar will be slightly higher than the blue bar.

Graph C best represents the relative rates

A. is wrong. The ice-to-water rate is faster, so the water is melting. The temperature is slightly above freezing (say, 3 °C).

B. is wrong. The two rates are equal, so the temperature is 0 °C.

D. is wrong. The water-to-ice rate (freezing) is much greater than the ice-to-water rate, so the temperature is well below freezing( say, -10 °C).