Question

The first vertical line in the diagram represents a thermometer with the melting points for ice and dry ice (melting point of ice is greater than that of dry ice) at normal atmospheric pressure. The numbered vertical lines represent possible melting points of both the substances at 10 atmospheric pressure. Which vertical line best represents the melting points of both the substances at 10 atmospheric pressure relative to the respective values at normal atmospheric pressure?
Note : The difference in temperatures are not to the scale.

• A. $1$
• B. $2$
• C. $3$
• D. $4$

Answer 1

The correct option is C $3$

As the pressure is increased from 1 atm to 10 atm, the melting point of ice slightly decreases and the melting point of dry ice slightly increases.

Hence, line 3 correctly represents the melting points of both substances at 10 atm pressure.

For most substances, with an increase in pressure, the melting point increases. Water is an exception as with the increase in pressure, the melting point decreases as the water expands when it goes from the liquid to the solid phase.

This can be explained by using the Clapeyron-Clausius formula. It can also be explained using LeChatelier's principle.