Chemistry • Year 12 • Module 5 • Lesson 7
Industrial Applications of Equilibrium & Collision Theory
Recall key vocabulary, the operating conditions of the Haber and Contact processes, and the four-component Band 6 structure for LCP responses.
1. Term–definition match
The definitions below are shuffled. Write the correct term from this list into the right-hand column: Haber process, Contact process, industrial compromise, heterogeneous catalyst, collision frequency, activation energy (Ea), Keq, yield, recycling, Le Chatelier’s Principle. 10 marks
| # | Definition (shuffled) | Matching term |
|---|---|---|
| 1.1 | The industrial synthesis of ammonia from nitrogen and hydrogen gases, run at approximately 450°C, 150–300 atm, using an iron catalyst. | |
| 1.2 | The industrial synthesis of sulfur trioxide from sulfur dioxide and oxygen, using a vanadium(V) oxide catalyst at approximately 450°C and 1–2 atm; part of the sulfuric acid production chain. | |
| 1.3 | The set of operating conditions chosen to balance reaction rate and equilibrium yield in a cost-effective way for an industrial process. | |
| 1.4 | A catalyst that exists in a different physical phase from the reacting species (e.g. a solid catalyst with gas-phase reactants). | |
| 1.5 | The minimum energy that colliding particles must possess for a reaction to occur. | |
| 1.6 | The equilibrium constant; a ratio of product to reactant concentrations at equilibrium that changes only with temperature. | |
| 1.7 | The number of effective collisions per unit time; increased by higher temperature, pressure, or concentration. | |
| 1.8 | The amount of desired product obtained; in industrial chemistry, a compromise between thermodynamic equilibrium position and rate of production. | |
| 1.9 | Returning unconverted reactants back into the reaction vessel to maximise overall product output despite low per-pass conversion. | |
| 1.10 | The principle stating that when a system at equilibrium is disturbed, it shifts in the direction that minimises the effect of the disturbance. |
2. True or false — with correction
Circle T or F. If false, write the corrected statement. 10 marks (1 T/F + 1 correction each)
2.1 The iron catalyst used in the Haber process increases both the rate of reaction and the equilibrium yield of ammonia. T / F
2.2 In the Haber process, increasing pressure shifts the equilibrium to the right because there are fewer moles of gas on the product side (2 mol) than on the reactant side (4 mol). T / F
2.3 Increasing temperature always increases the equilibrium yield of a chemical reaction. T / F
2.4 The Contact process uses vanadium(V) oxide (V2O5) as a heterogeneous catalyst to convert SO2 to SO3. T / F
2.5 In the Haber process, unreacted nitrogen and hydrogen gases are discarded after each pass through the reactor to prevent a build-up of reactants. T / F
3. Fill the blanks — Haber process conditions and reasoning
Complete the paragraph by writing one term or phrase in each blank. Word bank: 450, iron, 200, yield, rate, exothermic, left, condensation, recycled, 95, activation energy, compromise. 12 marks
The Haber process runs at approximately ____________°C, which represents a ____________ between reaction rate and equilibrium yield. The forward reaction (N2 + 3H2 → 2NH3) is ____________, so lower temperatures would give a higher equilibrium ____________ but an unacceptably slow ____________. An ____________ catalyst lowers the ____________ for both the forward and reverse reactions equally, allowing the system to reach equilibrium quickly without changing Keq. The plant operates at approximately ____________ atm of pressure. At equilibrium per pass, only 15–25% conversion is achieved; the equilibrium shifts to the ____________ as temperature increases. Ammonia is separated from unreacted gases by ____________ (NH3 liquefies at a higher temperature than N2 and H2), and the unreacted gases are ____________ back into the reactor, giving an overall conversion of over ____________%.
4. Function recall
Answer each in 1–2 sentences using precise terms from the lesson. 8 marks (2 each)
4.1 What does the iron catalyst do in the Haber process, and what does it not do?
4.2 Why is a temperature of 400–500°C chosen for the Haber process rather than room temperature (25°C)?
4.3 For the Contact process equilibrium (2SO2(g) + O2(g) ⇌ 2SO3(g), ΔH = −197 kJ mol−1), what is the effect of increasing temperature on: (a) the rate; (b) the equilibrium yield of SO3?
4.4 Explain why industrial plants do not simply use very high pressures (e.g. 1000 atm) in the Haber process to maximise yield.
5. Build a concept map
Draw labelled arrows between the six terms below to show how they are connected in the industrial compromise for the Haber process. Each arrow must carry a linking phrase. Aim for at least 6 labelled arrows. 6 marks
Supplied terms: temperature (450°C) · pressure (200 atm) · iron catalyst · recycling · rate of reaction · equilibrium yield.
Q1 — Term–definition matches
1.1 Haber process • 1.2 Contact process • 1.3 industrial compromise • 1.4 heterogeneous catalyst • 1.5 activation energy (Ea) • 1.6 Keq • 1.7 collision frequency • 1.8 yield • 1.9 recycling • 1.10 Le Chatelier’s Principle.
Q2 — True / false with corrections
2.1 False. The iron catalyst increases the rate of the Haber process but does NOT change the equilibrium yield (Keq is unchanged).
2.2 True. Correct: the Haber process has 4 mol of gas on the left (N2 + 3H2) and 2 mol on the right (2NH3), so increased pressure shifts the equilibrium to the side with fewer gas moles (right).
2.3 False. Increasing temperature increases yield only for endothermic forward reactions. For exothermic forward reactions (such as both the Haber and Contact processes), increasing temperature decreases equilibrium yield.
2.4 True.
2.5 False. Unreacted N2 and H2 are recycled (returned) to the reactor. This is the key strategy that achieves >95% overall conversion despite only 15–25% conversion per pass.
Q3 — Cloze answers (in order)
450 / compromise / exothermic / yield / rate / iron / activation energy / 200 / left / condensation / recycled / 95
Q4.1 — Catalyst function
The iron catalyst lowers the activation energy (Ea) for both the forward and reverse reactions equally, allowing the system to reach equilibrium much faster at 400–500°C. It does NOT change Keq or the equilibrium yield of ammonia.
Q4.2 — Why not room temperature?
At room temperature (25°C), Keq for the Haber process is very large (high thermodynamic yield would be possible), but the activation energy barrier is so large that the reaction rate is essentially zero even with a catalyst — the process would be commercially useless. The temperature of 400–500°C provides an acceptable rate of reaction while still giving a meaningful (if modest) per-pass yield.
Q4.3 — Contact process: temperature effects
(a) Rate increases: higher temperature gives particles more kinetic energy, increasing the proportion that exceed Ea and hence the collision frequency. (b) Equilibrium yield of SO3 decreases: the forward reaction is exothermic, so increasing temperature shifts equilibrium to the left (Le Chatelier’s Principle), reducing Keq and the proportion of SO3 at equilibrium.
Q4.4 — Why not 1000 atm?
Although higher pressure improves both yield and rate for the Haber process, the engineering costs for vessels, pumps, and seals able to withstand extremely high pressures increase exponentially. The additional ammonia produced at 1000 atm does not justify the enormous capital and safety costs. The limit is economic and engineering, not chemical.
Q5 — Sample concept map
Correct maps should include arrows such as:
- temperature (450°C) → is a compromise between → rate of reaction and equilibrium yield
- temperature (450°C) → increases → rate of reaction (but decreases equilibrium yield)
- iron catalyst → increases → rate of reaction
- iron catalyst → does not change → equilibrium yield
- pressure (200 atm) → increases both → rate of reaction and equilibrium yield
- recycling → compensates for low per-pass → equilibrium yield
Any biologically valid linking phrases accepted. Award 1 mark per correctly labelled arrow respecting causal direction (max 6).