Answer to Question #148238 in General Chemistry for Saqib

Question

Explain Gibbs free energy with examples

Answer 1

Gibbs Free Energy (G) - The energy associated with a chemical reaction that can be used to do work. The free energy of a system is the sum of its enthalpy (H) plus the product of the temperature (Kelvin) and the entropy (S) of the system

Δ G = Δ H − T Δ S

In terms of examples, I am unsure on whether you meant real life examples or calculation examples, therefore I will provide both down below.

Gibbs Free Energy is simply just an equation that is used to calculate if a reaction is spontaneous or not. An example problem would be:

Estimate the temperature where ΔG = 0 for the following reaction: (Given: ΔH = -176 kJ and ΔS = -284.5 J/K) CAUTION: Beware of units.

NH3(g) + HCl(g) ---> NH4Cl(s)

Using the equation above, we seperate T to be on one side, giving us (G+H)/S = T. Then we subsitute the values in the equation. As how the question states it, Beware of units!

1 J = 1000kJ, therefore -284.5 J/K/1000 gives us -0.2845 kJ.

By subsituting this value in the equation for S, you should be able to obtain the answer 619K.