Question

Consider the following chemical reaction, which is exothermic:
CO(g) + NO2(g) ® CO2(g) + NO(g)

Sketch a potential energy diagram of this reaction, and label the following quantities: Ea(fwd), Ea(rev), DH, activated complex, products, reactants, x-axis, and y-axis.

Answer 1

I can’t draw pictures directly here, but below is a simple ASCII potential-energy diagram you can copy/trace and the labels you should add.

Diagram (left = reactants, right = products):

Energy
|
| ___
| / \ ← activated complex (transition state)
| / \
| Reactants / \ ← Products (lower energy because reaction is exothermic)
| CO + NO2 / \ CO2 + NO
|---------/--------------\------------------> Reaction coordinate
↑ ↑
| |
Ea(fwd) Ea(rev)

Add these explicit labels:
- y-axis: “Potential energy (or Energy)”
- x-axis: “Reaction coordinate”
- Left point on curve baseline: “Reactants: CO(g) + NO2(g)”
- Peak of curve: “Activated complex (transition state)”
- Right point on curve baseline (lower than reactants): “Products: CO2(g) + NO(g)”
- Arrow from reactants up to peak: “Ea(fwd)” (activation energy for the forward reaction)
- Arrow from products up to peak: “Ea(rev)” (activation energy for the reverse reaction)
- Vertical arrow between reactants and products (downward): “ΔH (negative for exothermic)” — you can label ΔH = Eproducts − Ereactants (a negative value here)

Notes:
- Because the reaction is exothermic, products are at lower energy than reactants, so ΔH < 0.
- Ea(rev) = Ea(fwd) + |ΔH|, so the reverse activation energy is larger than the forward activation energy.