Calculating ?S for a Reaction

Consider 2 H2(g) + O2(g) ? 2 H2O(liq)

DSo = 2 So (H2O) - [2 So (H2) + So (O2)]

DSo = 2 mol (69.9 J/K•mol) -

[2 mol (130.7 J/K•mol) + 1 mol (205.3 J/K•mol)]

DSo = -326.9 J/K

Note that there is a decrease in S because 3 mol of gas give 2 mol of liquid.

DSo = S So (products) - S So (reactants)

If S DECREASES,

why is this a SPONTANEOUS REACTION??

Previous slide

Next slide

Back to first slide

View graphic version