Question

H2O(g) → H2 + O2(g) Predict whether the reaction above would have an increase or a decrease in entropy.

Answer 1

Since the reaction has one mole of reactants versus two moles of products, the reaction would have a decrease in entropy. One mole of gas exerts less pressure than two moles of gas, and therefore one mole of gas has more entropy than two moles of gas.

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Answer 2

Answer: The reaction
`H_2O(g)\rightarrow H_2(g)+O_2(g)` would have increase in entropy.

Explanation: Entropy is the measure of degree of randomness or disorder of a system. Thus a system with less disorder has less entropy and a system with more disorder has more entropy. The balanced chemical equation will be:

`2H_2O(g)\rightarrow 2H_2(g)+O_2(g)`

The given reaction leads to formation of 3 moles of gaseous products from 2 mole of gaseous reactant. Thus the given reaction leads to increase in moles and thus increase in disorder and increase in entropy.