Answer to Question #332121 in General Chemistry for Ash

Question

Predict whether the entropy change of the system in each of the following is positive or negative

1. O2(g) —> 2O(g)

2. N2 (g, 10 atm) —> N2 (g, 1atm).

3. 6CO2(g) + 6H2O(g) —> C6H12O6(g) + 6O2(g).

4. 2 H2 (g) + O2 (g) —> 2 H2O (l)

5. NH4Cl (s) —> NH3(g) + HCl (g)

Answer 1

Whenever there is an increase in moles in the reaction, then entropy increases.

So change in entropy is positive. And whenever the moles on the product side are more than reactants, then entropy decreases.

1) O₂ (g) —> 2O (g). In this reaction one mole of Oxygen is broken into 2 moles. So moles of product is more than moles of reactant. Therefore change is entropy will be positive in this case.

2) N₂ (g, 10 atm) —> N₂ (g, 1atm).

3) 6CO₂ (g) + 6H₂O (g) —> C₆H₁₂O₆ (g) + 6O₂ (g). In this reaction, the moles on the reactant side is greater than the moles on the product side. So change in entropy will be negative in this case.

4) 2H₂ (g) + O₂ (g) —> 2H₂O (l). In this reaction, the moles on the reactant side is greater than the moles on the product side. Also the reactants are gaseous and product is liquid. So change in entropy will be negative in this case.

5) NH₄Cl (s) —> NH₃(g) + HCl (g). In this reaction one mole of NH₄Cl is broken into 2 moles. So moles of product is more than moles of reactant. Also products are gaseous and reactant is solid. Therefore change is entropy will be positive in this case.