Question

The heat of fusion of dichloromethane (CH2Cl2) is 6.2 kJ/mol.

Calculate the change in entropy Δs when 345 g of dichloromethane freezes at -95.1 °C.
Be sure your answer contains a unit symbol and the correct number of significant digits.

Answer 1

Answer : The entropy change of the dichloromethane is 142 J/K

Explanation :

To calculate the number of moles, we use the equation:

`\text{Number of moles}=\frac{\text{Given mass}}{\text{Molar mass}}`

Given mass of dichloromethane = 345 g

Molar mass of dichloromethane = 84.93 g/mol

Putting values in above equation, we get:

`\text{Moles of dichloromethane}=(345g)/(84.93g/mol)=4.06mol`

To calculate the entropy change for different phase at same temperature, we use the equation:

`\Delta S=n* (\Delta H_(fusion))/(T)`

where,

`\Delta S` = Entropy change = ?

n = moles of dichloromethane = 4.06 moles

`\Delta H_(fusion)` = enthalpy of fusion = 6.2 kJ/mol = 6200 J/mol (Conversion factor: 1 kJ = 1000 J)

T = temperature of the system =
`-95.1^oC=[-95.1+273]K=177.9K`

Putting values in above equation, we get:

`\Delta S=(4.06mol* 6200J/mol)/(177.9K)\\\\\Delta S=141.495J/K\approx 142J/K`

Hence, the entropy change of the dichloromethane is 142 J/K