Question

consider a hypothetical chemical reaction: ( a + b
ightarrow c + d ) (in this equation ( a ), ( b ), ( c ) and ( d ) stand for some unknown chemical formulas.) here is an energy diagram for the reaction: use the energy diagram to answer these questions. what is the heat of reaction? ( \text{kj/mol} ) is the reaction exothermic or endothermic? exothermic endothermic neither can you determine the activation energy? yes, its ( \text{kj/mol} ) no. can you determine the activation energy of the reverse reaction? ( c + d
ightarrow a + b ) yes, its ( \text{kj/mol} ) no.

Explanation:

Step1: Calculate heat of reaction

Heat of reaction \( \Delta H=\text{Energy of products}-\text{Energy of reactants}\).
From the graph, energy of \(A + B\) (reactants) is \(250\space kJ/mol\), energy of \(C + D\) (products) is \(50\space kJ/mol\).
\(\Delta H = 50 - 250=- 200\space kJ/mol\)

Step2: Determine reaction type

Since \(\Delta H=-200\space kJ/mol<0\), heat is released. So the reaction is exothermic.

Step3: Calculate activation energy

Activation energy is the energy difference between reactants and the peak of the energy curve.
Energy of \(A + B\) is \(250\space kJ/mol\), peak energy is \(400\space kJ/mol\).
Activation energy \(E_a=400 - 250 = 150\space kJ/mol\)

Step4: Calculate activation energy of reverse reaction

For the reverse reaction \(C + D
ightarrow A + B\), activation energy is the energy difference between products (\(C + D\)) and the peak of the energy curve.
Energy of \(C + D\) is \(50\space kJ/mol\), peak energy is \(400\space kJ/mol\).
Activation energy of reverse reaction \(E_{a(\text{reverse})}=400 - 50=350\space kJ/mol\)

Answer:

• What is the heat of reaction? \(-200\space kJ/mol\)
• Is the reaction exothermic or endothermic? Exothermic
• Can you determine the activation energy? Yes, it's \(150\space kJ/mol\)
• Can you determine the activation energy of the reverse reaction \(C + D

ightarrow A + B\)? Yes, it's \(350\space kJ/mol\)