Question

consider a hypothetical chemical reaction:

$a + b \to c + d$

(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?	$\square$ kj/mol
can you determine the activation energy?	$\bigcirc$ yes, its $\square$ kj/mol<br>$\bigcirc$ no.
can you determine the activation energy of the reverse reaction?<br>$c + d \to a + b$	$\bigcirc$ yes, its $\square$ kj/mol<br>$\bigcirc$ no.

Explanation:

Step1: Calculate the heat of reaction

The heat of reaction ($\Delta H$) is calculated as the energy of products minus the energy of reactants.
From the diagram, energy of reactants ($A + B$) is approximately $50\ \text{kJ/mol}$ and energy of products ($C + D$) is approximately $300\ \text{kJ/mol}$.
$$\Delta H=E_{products}-E_{reactants}=300 - 50=250\ \text{kJ/mol}$$
Since $\Delta H>0$, the reaction is endothermic.

Step2: Determine activation energy

Activation energy ($E_a$) is the energy difference between the transition state (highest point on the energy diagram) and the reactants.
From the diagram, if we assume the transition - state energy is at the peak. Let's say the reactant energy ($A + B$) is $50\ \text{kJ/mol}$ and the peak is at $350\ \text{kJ/mol}$ (approximate visual estimate).
$$E_a = 350 - 50=300\ \text{kJ/mol}$$

Step3: Determine activation energy of the reverse reaction

For the reverse reaction ($C + D
ightarrow A + B$), activation energy ($E_{a,\text{reverse}}$) is the energy difference between the transition state and the products ($C + D$).
$$E_{a,\text{reverse}}=350 - 300 = 50\ \text{kJ/mol}$$

Answer:

• What is the heat of reaction? $250\ \text{kJ/mol}$
• Is the reaction exothermic or endothermic? Endothermic
• Can you determine the activation energy? Yes, it's $300\ \text{kJ/mol}$
• Can you determine the activation energy of the reverse reaction $C + D

ightarrow A + B$? Yes, it's $50\ \text{kJ/mol}$