For which of the following reactions would the entropy of reaction (S°rxn) be po

Question

For which of the following reactions would the entropy of reaction (S°rxn) be positive (an increase in entropy for the system)? Select all that apply.

A. The dissolution of sodium chloride (table salt): NaCl (s) Na+ (aq) + Cl– (aq)

B. The dissolution of sucrose (sugar): C12H22O11 (s) C12H22O11 (aq)

C. The deposition of water vapor to give ice: H2O (g) H2O (s)

D. The combustion of heptane (a component of gasoline): C7H16 (l) + 11 O2 (g) 7 CO2 (g) + 8 H2O (g)

E. None of the above will have a positive entropy of reaction.

Explanation / Answer

If a chemical reaction has a positive change in entropy, S, then the disorder of the system increases.

A. The dissolution of sodium chloride (table salt): NaCl (s) Na+ (aq) + Cl– (aq) ENTROPY INCREASES

B. The dissolution of sucrose (sugar): C12H22O11 (s) C12H22O11 (aq) ENTROPY  INCREASES

Entropy increases every time a solute dissolves in a solvent.

C.The deposition of water vapor to give ice: DECREASE IN ENTROPY. DIS ORDERNESS DECREASES

D. The combustion of heptane ENTROPY INCREASES

The increase in gas molecules increases the disorder, and therefore the change in entropy is positive.

there are 12 molecules of gas on the left, and 15 molecules of gas on the right. The increase in gas molecules increases the disorder, and therefore the change in entropy is positive.

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