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), H, activated complex, products, reactants, x-axis, and y-axis.

Answer 1

I can’t draw a picture here, but below is a clear description and a simple ASCII sketch you can copy or use to draw the required potential-energy diagram.

How to draw it
1. Draw a vertical axis and label it "Potential energy (y‑axis)".
2. Draw a horizontal axis and label it "Reaction coordinate (x‑axis)". Reactants at left, products at right.
3. At the left, mark a horizontal line and label it "Reactants: CO(g) + NO2(g)".
4. From that line draw a curve rising to a single peak (transition state/activated complex), then dropping to a lower horizontal line on the right. Label the right line "Products: CO2(g) + NO(g)". (Products should be lower than reactants because the reaction is exothermic.)
5. At the top of the peak label "Activated complex (transition state)".
6. Draw a vertical arrow from the reactants energy up to the peak and label it Ea(fwd) (activation energy, forward).
7. Draw a vertical arrow from the products energy up to the peak and label it Ea(rev) (activation energy, reverse).
8. Draw a vertical arrow (or double‑headed arrow) from the reactants energy down to the products energy and label it ΔH. Because the reaction is exothermic, ΔH is negative (products lower than reactants).

Simple ASCII sketch

Potential energy (y)
|
Reactants | /\ <-- activated complex (transition state)
CO + NO2 -----|--------/ \---------
| / \ <-- Ea(fwd) = from reactants up to peak
| / \
| / \ <-- Ea(rev) = from products up to peak
| / \
| / \
Products ------|--/--------------\---- CO2 + NO
|
+-------------------------------- Reaction coordinate (x)

Label meanings and relationships
- Activated complex (transition state): the highest point (peak) on the curve.
- Ea(fwd): vertical energy difference from reactants to the peak.
- Ea(rev): vertical energy difference from products to the peak.
- ΔH = E_products − E_reactants (here ΔH < 0 because products are lower = exothermic).
- Mathematical relation: Ea(rev) = Ea(fwd) − ΔH. (Since ΔH is negative for exothermic, Ea(rev) > Ea(fwd).)

That yields the required labeled potential energy diagram for the exothermic reaction CO + NO2 → CO2 + NO.