Question

What is ΔSsys for a condensation phase transition at 26.5 °C for a compound that condenses at 26.5 °C and the ΔHsys = -40.1 kJ mol-1 for this process?

Answer 1

The entropy change (ΔSsys) for the condensation phase transition is calculated using the thermodynamic relation ΔSsys = ΔHsys/T with ΔHsys = -40.1 kJ/mol and the temperature of 26.5 °C converted to Kelvin (299.65 K), yielding ΔSsys = -133.9 J/mol·K.

Step-by-step explanation:

To calculate the entropy change (ΔSsys) for a condensation phase transition, we can use the following thermodynamic relation:

ΔSsys = ΔHsys/T

To proceed, we must ensure that the units are consistent, so we convert the ΔHsys value from kilojoules to joules:

ΔHsys = -40.1 kJ/mol × 1000 J/kJ = -40100 J/mol

Next, we convert the temperature from Celsius to Kelvin:

T = 26.5 °C + 273.15 = 299.65 K

Now we can substitute the values into the equation to find ΔSsys:

ΔSsys = -40100 J/mol / 299.65 K

This gives:

ΔSsys = -133.9 J/mol·K

The negative value indicates a decrease in entropy, as expected for a condensation process where the disorder of the system decreases when gas becomes liquid.