Unit 10
Chemical equilibrium
The brown NO₂ in a sealed flask looks perfectly still, yet molecules pair up and split apart countless times a second. This unit starts from a molecule-by-molecule simulation, builds up the equilibrium constant and the reaction quotient, solves equilibrium compositions exactly with ICE tables, tests Le Chatelier’s principle on real colour-changing systems, and finally recomputes the yield — and the compromise — of the Haber process from thermodynamic data.
- 1 Dynamic equilibrium: both directions at once Reversible reactions never “stop”: the forward reaction slows and the reverse speeds up until the two are equal. Watch a molecule-by-molecule simulation reach the same equilibrium from both ends. 20 min
- 2 The equilibrium constant and the reaction quotient Whatever mixture you start from, [HI]²/([H₂][I₂]) ends up near 54. Write K, tell Kc from Kp, deal with solids and pure liquids, and predict the direction of change by comparing Q with K. 25 min
- 3 Equilibrium calculations: ICE tables Initial, change, equilibrium: three rows turn any equilibrium problem into one equation in x. See how exact root finding solves it — and when the shortcut fails. 25 min
- 4 Le Chatelier’s principle: how equilibria respond Add a reagent, compress, heat — disturb real colour-changing equilibria (cobalt chloride, iron thiocyanate, NO₂), watch them shift, and see why they only partly undo the change. 30 min
- 5 The Haber process: an industrial compromise At room temperature K is enormous but the reaction is hopelessly slow; heating speeds it up but pushes the equilibrium back. Compute the yield from thermodynamic data and see where 450 °C and 200 bar come from. 25 min