Question

For which of these is there an increase in entropy? KCI(aq)+AgNO3(aq)KNO3(aq)+AgCI(s) NaCl(s)NaCl(aq) 2NaOH(aq)+CO2(g)Na2CO3(aq)+H20(1) C2H5OH(g)C2H5OH(I)

Answer 1

Answer: NaCl (s) → NaCl (aq)

Explanation:

Entropy is often associated with the disorder or randomness of a system. Therefore, in each reaction, it is necessary to evaluate if the disorder increases or decreases to understand what happens to the entropy:

1) KCl (aq) + AgNO₃ (aq) → KNO₃ (aq) + AgCl (s) - In this reaction, we have only aqueous reactants in the beginning and in the product we have a precipitate. The solid state is more organised than the liquid, consequently, the entropy decreases.

2) NaCl (s) → NaCl (aq) - In this case, oposite to the first one, we go from a solid state to an aqueous state. The solvation of the ions Na⁺ and Cl⁻ is random while the solid state is very organised. Therefore, in this reaction the entropy increases.

3) 2NaOH (aq) + CO₂ (g) → Na₂CO₃ (aq) + H₂O (l) - In this reaction, the reactants have higher entropy because of the gas CO₂. Therefore, the entropy decreases.

4) C₂H₅OH (g) → C₂H₅OH (l) -  In this reaction, the reactant is a gas and the product a liquid. Therefore, the entropy decreases.