Chemical equilibrium explorer
Watch a reversible reaction reach dynamic equilibrium, then change concentration, pressure, temperature or catalyst and compare Qc with Kc as it settles again.
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Learning objectives
- state that some chemical reactions are reversible, e.g. manufacture of ammonia
- interpret data relating to the conditions used in industry for processes involving reversible reactions, e.g. manufacture of ammonia by the Haber Process (knowledge of Le Chatelier’s Principle is not required).
- explain, in terms of rates of the forward and reverse reactions, what is meant by a reversible reaction and dynamic equilibrium
- state Le Chatelier’s Principle and apply it to deduce qualitatively (from appropriate information) the effects of changes in concentration, pressure or temperature, on a system at equilibrium
- deduce whether changes in concentration, pressure or temperature or the presence of a catalyst affect the value of the equilibrium constant for a reaction
- deduce expressions for equilibrium constants in terms of concentrations, Kc
- calculate the values of equilibrium constants in terms of concentrations from appropriate data
- describe and explain the conditions used in the Haber process, as an example of the importance of an understanding of chemical equilibrium in the chemical industry
- Dynamic Equilibrium and Le Chatelier
- Equilibrium Constants (Kc and Kp)
- Haber Process (Case Study)
[N₂] = 1.00 mol/dm³, [H₂] = 3.00 mol/dm³, [NH₃] = 0 mol/dm³ at 450 °C. Qc is less than Kc, so the forward reaction is faster.
- [N₂]
- 1.00 mol/dm³
- [H₂]
- 3.00 mol/dm³
- [NH₃]
- 0 mol/dm³
- [NO₂]
- 1.00 mol/dm³
- [N₂O₄]
- 3.00 mol/dm³
- Qc
- 0
- Kc
- 0.185
- Pressure
- 237 atm
- NH₃ at equilibrium
- 25.9 %
- Relative rate
- 0.13
Try this
0 of 4 doneLet nitrogen and hydrogen reach equilibrium, then add nitrogen and watch equilibrium re-establish. (not done yet)
Adding N₂ makes Qc smaller than Kc, so the forward reaction speeds up until the rates are equal again. Some of the added N₂ is used up, more NH₃ forms, and Kc is unchanged.
Squeeze the NO₂ and N₂O₄ syringe at equilibrium and watch the colour. (not done yet)
Squeezing raises every concentration, so the brown darkens at once. The mixture then shifts towards N₂O₄, which has fewer gas molecules, and the colour partly fades.
Heat an equilibrium mixture and compare Kc before and after. (not done yet)
Both forward reactions are exothermic (ΔH is negative), so heating lowers Kc and the mixture shifts left. Only a temperature change alters Kc.
In Haber conditions, compare the ammonia content and the rate at 350 °C and at 450 °C at the same pressure. (not done yet)
A lower temperature gives more ammonia at equilibrium but reaches it far more slowly. Plants use about 450 °C with an iron catalyst as a compromise, and about 200 atm because higher pressures cost more to build and run.