Question

Given the following information

A + B --> 2D delta H =684.9kJ delta S= 298.0J/K

C --> D delta H= 503.0kJ delta S=-103.0J/K

calculate ΔG° for the following reaction at 298 K.

A + B --> 2C

Answer 1

Lets number the reaction as 1, 2, 3 from top to bottom

required reaction should be written in terms of other reaction

This is Hess Law

required reaction can be written as:

reaction 3 = +1 * (reaction 1) -2 * (reaction 2)

So, deltaHo rxn for required reaction will be:

deltaHo rxn = +1 * deltaHo rxn(reaction 1) -2 * deltaHo rxn(reaction 2)

= +1 * (684.9) -2 * (503.0)

= -321.1 KJ

deltaSo rxn for required reaction will be:

deltaSo rxn = +1 * deltaSo rxn(reaction 1) -2 * deltaSo rxn(reaction 2)

= +1 * (298.0) -2 * (103.0)

= 92.0 J/K

deltaHo = -321.1 KJ

deltaSo = 92 J/K

= 0.092 KJ/K

T = 298 K

we have below equation to be used:

deltaGo = deltaHo - T*deltaSo

deltaGo = -321.1 - 298.0 * 0.092

deltaGo = -348.5 KJ

Answer: -348.5 KJ