To determine which reactions have a positive change in entropy (ΔSrxn), we should look at the number of gas moles on both sides of the reaction. A positive ΔSrxn typically suggests that the products have more disorder (or more moles of gas) than the reactants.
- A: g + b g → 3c g
- Reactants: 2 moles (g + b g), Products: 3 moles (3c g) – Positive ΔSrxn
- B: 2a g + b g → c g
- Reactants: 3 moles (2a g + b g), Products: 1 mole (c g) – Negative ΔSrxn
- C: a g + 2b g → 2c g
- Reactants: 3 moles (a g + 2b g), Products: 2 moles (2c g) – Negative ΔSrxn
- D: 2a g + b s → 3c g
- Reactants: 2 moles of gas + 1 mole of solid, Products: 3 moles of gas – Positive ΔSrxn
In summary, the reactions with a positive ΔSrxn are:
- A: g + b g → 3c g
- D: 2a g + b s → 3c g