Le Chatelier's principle template

Le Chatelier's principle for GCSE, A-level and NCERT Class 11: what each change does to the position of equilibrium and to K, a concentration–time graph for adding H₂ to H₂ + I₂ ⇌ 2HI (K unchanged), and four colour equilibria (N₂O₄/NO₂, cobalt chloride, chromate/dichromate, iron(III) thiocyanate).

What the template shows

• A system at equilibrium shifts to oppose a change in concentration, pressure or temperature; only temperature changes K
• What each change does
• Position of equilibrium
• Add a reactant
• Shifts right, using up some of what was added
• Remove a product
• Shifts right, replacing some of it
• Raise pressure (gases)
• Shifts to the side with fewer moles of gas
• Raise temperature
• Shifts in the endothermic direction
• Changes (up if forward ΔH > 0)
• Add a catalyst
• No shift; equilibrium reached sooner
• concentration / mol dm⁻³
• Kc = [HI]² / ([H₂][I₂]) = 49 before and 49 after
• Some of the added H₂ reacts with I₂: [HI] rises, [I₂] falls, until the ratio is back to K. Illustrative concentrations.
• Seeing the shift: colour equilibria
• Heat: browner (endothermic way). Squeeze: paler after the first darkening (fewer moles on the left).
• Heat or add conc. HCl: blue. Cool or add water: pink.
• controlled by pH (not redox)
• Add acid: orange. Add alkali (removes H⁺): yellow.
• pale yellow
• blood red

Drawn with 357 shapes – every one editable in MolDraw.

Sources

• Atkins, de Paula & Keeler, Atkins' Physical Chemistry, 11th ed., OUP 2018, ch. 6 Textbook
• NCERT, Chemistry Part I, Class XI, ch. 6 Equilibrium Textbook