Which of the following reactions have a positive ÄSrxn? Check all that apply.
A(g) + B(g)--> C(g)
2A(g) + B(g)--> 4C(g)
A(s) + B(g)--> 2C(g)
2A(g) + 2B(g)--> 3C(g)
To determine if a reaction has a positive ΔSrxn (change in entropy), you need to consider the number of moles of gas on both sides of the reaction equation. The general rule is that if the number of moles of gas increases in the reaction, then ΔSrxn will be positive.
Let's examine each reaction:
A(g) + B(g) --> C(g)
In this reaction, there are 2 moles of gas on the reactant side and 1 mole of gas on the product side. Since the number of moles of gas decreases, ΔSrxn will be negative.
2A(g) + B(g) --> 4C(g)
In this reaction, there are 3 moles of gas on the reactant side and 4 moles of gas on the product side. Since the number of moles of gas increases, ΔSrxn will be positive.
A(s) + B(g) --> 2C(g)
In this reaction, there is 1 mole of gas on the reactant side, and 2 moles of gas on the product side. Since the number of moles of gas increases, ΔSrxn will be positive.
2A(g) + 2B(g) --> 3C(g)
In this reaction, there are a total of 4 moles of gas on the reactant side and 3 moles of gas on the product side. Since the number of moles of gas decreases, ΔSrxn will be negative.
Based on these analyses, the reactions that have a positive ΔSrxn are:
- 2A(g) + B(g) --> 4C(g)
- A(s) + B(g) --> 2C(g)