Multiple Choice
A negative change in entropy, , indicates that which of the following is true for the system?
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19. Chemical Thermodynamics
Entropy
Multiple Choice
Which of the following reactions would result in a decrease in entropy (i.e., ) under standard conditions?
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Verified step by step guidance1
Recall that entropy (S) is a measure of disorder or randomness in a system. A decrease in entropy (ΔS < 0) means the system becomes more ordered after the reaction.
Analyze each reaction by comparing the number of moles and physical states of reactants and products, since gases generally have higher entropy than liquids or solids.
For the reaction \(2\,H_2(g) + O_2(g) \rightarrow 2\,H_2O(l)\), note that gaseous reactants form liquid water, which is more ordered, so entropy decreases.
For the other reactions, check if the number of gas molecules increases or if solids decompose into gases, which usually increases entropy (ΔS > 0).
Conclude that the reaction forming liquid water from gases results in a decrease in entropy because it reduces the number of gas molecules and forms a more ordered liquid phase.
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