Question

Liquid benzene freezes at 5.5oC. At this temperature, the densities of liquid and solid benzene are 0.879 g cm-3 and 0.891 g cm-3, respectively. Find the molar volume change when solid benzene melts at this temperature.

Answer 1

Solution

The molar mass of benzene = 78.11 g/mol
Density of liquid benzene at 5°C = 0.879 g/cm-1 = 0.879 g/mL

Density of solid benzene at 5°C = 0.891 g/cm-1 = 0.891 g/mL

We know that

Molar volume = molar mass of benzene / Density of benzene

The molar mass of liquid benzene = (78.11 g/mol)/(0.879 g/mL) = 88.862 mL/mol

The molar mass of solid benzene = (78.11 g/mol)/(0.891 g/mL) = 87.666 mL/mol

Molar volume change when solid benzene melts =(87.666 - 88.862) mL/mol = -1.196 mL/mol

Thus, the molar volume of liquid benzene is increased with 1.196 mL/mol when solid benzene melts.