Answer:
1) Reaction A is exothermic.
2) Reaction B is exothermic.
3) Reaction pathway B has the faster rate because the activation energy is smaller than the activation energy of reaction pathway A.
4) Reaction B has a larger ΔHrxn. Larger in the exothermic sense (Larger negative value)
Explanation:
The missing graph of the reaction pathway for A and B is attached to this solution.
1) Reaction pathway A is
- exothermic.
- neither exothermic nor endothermic.
- endothermic.
The heat of reaction is what determines whether a reaction is exothermic or endothermic. It is exothermic if the heat of reaction is negative and endothermic if the heat of reaction is positive.
The heat of reaction of a reaction is given as the heat of products minus the heat of reactants.
ΔHrxn = H°(products) - H°(reactants)
The H°(products) are read from the graph as the right hand side of the graph after the peak and the H°(reactants) is read from the left hand side of the graph, before the peak.
And from the graph it evident that
H°(products) < H°(reactants)
Hence ΔHrxn for this reaction is negative. And this means that the reaction is negative.
2) Reaction pathway B is
- exothermic.
- neither exothermic nor endothermic.
- endothermic
The explanation for this is just similar to that of the first question. This reaction too is exothermic.
3) Which pathway has the faster rate of reaction and why?
- Reaction pathway B has the faster rate because the products have less energy than the products of reaction pathway A.
- Reaction pathway A has the faster rate because the products have more energy than the products of reaction pathway B.
- Reaction pathway B has the faster rate because the activation energy is smaller than the activation energy of reaction pathway A.
- Reaction pathway A has the faster rate because the activation energy is greater than the activation energy of reaction pathway B.
The rate of reaction depends on a number of factors and one of them is the activation energy.
The activation energy of a reaction is the energy the reactants of a reaction must possess before a reaction can occur. It is read from the graph as the difference between the peak of the graph and the energy of the reaction.
The rate of the reaction increases as the the activation energy of the reaction reduces.
Hence, the reaction B with the smaller activation energy (evident from the graph) has the faster rate of reaction.
4) Which reaction pathway has the larger heat of reaction, Δ H rxn ? ΔHrxn?
As described in question 1, the heat of reaction is given as
ΔHrxn = H°(products) - H°(reactants)
The two reactions have the same H°(reactants)
But
H°(products) for reaction B < H°(products) for reaction A.
Hence
ΔHrxn = H°(products) - H°(reactants) for reaction B would result in a bigger negative value than
ΔHrxn = H°(products) - H°(reactants) for reaction A.
Hence, reaction B is said to have the bigger heat of reaction. Since they are both exothermic reactions, it means reaction B will give off a bigger heat of reaction.
Hope this Helps!!!!
