For 1719 consider the phase diagram to the right 17 The slop

For #17-#19 consider the phase diagram to the right 17. The slope of curve A-B is negative because (A) Sm(liq)>Sm(sol) (C) Vm(liqjcVm(sol) (B) Sm(lia) Sm(sol) (D) Vm(liq)>Vm(sol)

Solution

The slope of the curve is negative and the correct option is (C).

Normally the solid/liquid phase line slopes positively to the right, However for other substances, notably water, the line slopes to the left as the diagram for water given in the question. This indicates that the liquid phase is denser than the solid phase. This phenomenon is caused by the crystal structure of the solid phase. In the solid forms of water and some other substances, the molecules crystallize in a lattice with greater average space between molecules, thus resulting in a solid with a lower density than the liquid. Because of this phenomenon, one is able to melt ice simply by applying pressure and not by adding heat