Which of the following reactions have a positive delta S rxn? check all that apply
1) A(s)+2B(g) -->C(g)
2) 2A(g)+3B(g) -->4C(g)
3) 2A(g)+2B(g) -->5C(g)
4) 2A(g)+B(s) -->3C(g)
Not sure how to tell if the reaction is positive.
To determine if a reaction has a positive ΔS_rxn (change in entropy), you need to consider the entropy changes for the reactants and products.
The general rule is that an increase in the number of moles of gas or a reaction that produces more gas molecules will have a positive ΔS_rxn.
Let's analyze each reaction:
1) A(s) + 2B(g) --> C(g)
This reaction has 3 moles of gas on the reactant side (2 moles of B(g) and 1 mole of A(s)), and 1 mole of gas on the product side (1 mole of C(g)). Therefore, this reaction does not have a positive ΔS_rxn.
2) 2A(g) + 3B(g) --> 4C(g)
This reaction has 5 moles of gas on the reactant side (2 moles of A(g) and 3 moles of B(g)), and 4 moles of gas on the product side (4 moles of C(g)). Therefore, this reaction has a positive ΔS_rxn.
3) 2A(g) + 2B(g) --> 5C(g)
This reaction has 4 moles of gas on the reactant side (2 moles of A(g) and 2 moles of B(g)), and 5 moles of gas on the product side (5 moles of C(g)). Therefore, this reaction has a positive ΔS_rxn.
4) 2A(g) + B(s) --> 3C(g)
This reaction has 2 moles of gas on the reactant side (2 moles of A(g)), and 3 moles of gas on the product side (3 moles of C(g)). Therefore, this reaction does not have a positive ΔS_rxn.
Based on this analysis, the reactions that have a positive ΔS_rxn are:
- 2A(g) + 3B(g) --> 4C(g)
- 2A(g) + 2B(g) --> 5C(g)
To determine if a reaction has a positive ΔS (change in entropy of the system), you need to examine the number and type of moles of gas on the reactant and product sides.
First, identify the coefficients of the reactants and products in the balanced chemical equation provided.
1) A(s) + 2B(g) → C(g)
2) 2A(g) + 3B(g) → 4C(g)
3) 2A(g) + 2B(g) → 5C(g)
4) 2A(g) + B(s) → 3C(g)
Once you have determined the coefficients, count the number of moles of gas on the reactant and product sides of the equation.
1) Reactant side: 2 moles of gas, product side: 1 mole of gas
2) Reactant side: 5 moles of gas, product side: 4 moles of gas
3) Reactant side: 4 moles of gas, product side: 5 moles of gas
4) Reactant side: 3 moles of gas, product side: 3 moles of gas
To determine if ΔS is positive, you need to look for an increase in the number of moles of gas. When the number of moles of gas increases from reactants to products, the system has more molecular randomness and greater entropy.
Based on this, the reactions that have a positive ΔS rxn are:
- Reaction 2: 2A(g) + 3B(g) → 4C(g)
- Reaction 3: 2A(g) + 2B(g) → 5C(g)