John T. answered • 07/14/21
Tutor
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Ph.D. in Chemistry from Yale with 17+ Years of Teaching Experience
Given that H2O(g) + CO(g) → H2(g) + CO2(g) with ΔG°rxn = -28.6 kJ...
RULE #1: If you reverse a reaction, then the sign of ∆G changes. So:
H2(g) + CO2(g) → H2O(g) + CO(g) with ΔG°rxn = +28.6 kJ
What you notice now is that the reaction in question is 7 times this reaction.
RULE #2: If you scale a reaction by some factor, then the magnitude of ∆G changes by that same factor. So:
7 H2(g) + 7 CO2(g) → 7 H2O(g) + 7 CO(g) will have ΔG°rxn = 7 * 28.6 = +200.2 kJ.
Your answer should probably stay with three significant figures, which means it should be 200. kJ
