How do you calculate the change in Gibbs free energy (∆G) for the following reactions at 25 °C?

Question

$Ca(s) + 2H_2O(l) → Ca(OH)_2(s) + H_2(g)$
∆H = -411.6 kJ/mol
∆S = 31.8 J/mol∙K?

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Answer 1 · 2016-04-25T12:06:19

You can do it like this:

Use this relationship which arises from the 2nd law of thermodynamics:

$DeltaG=DeltaH-TDeltaS$

$DeltaH$ is the enthalpy change

$T$ is the absolute temperature

$DeltaS$ is the entropy change

Putting in the values:

$DeltaG=-411xx10^(3)-(298xx31.8)$

$DeltaG=-411xx10^(3)-(9.476xx10^(3))$

$DeltaG=-421.07" ""kJ/mol"$