Chemistry · Rung 24 of 24

Chemical equilibrium

An equilibrium is not anything stopping: the reaction keeps going both ways, just at the same rate, so the amounts stop changing. It is a dynamic stalemate, like walking down an up escalator. And equilibrium does not mean half and half: there can be ninety per cent on one side, and that is what the equilibrium constant tells you — large, mostly products; small, mostly reactants. What the constant does not tell you is how long it takes to get there, which is the rate and is another matter: diamond is turning into graphite right now, very slowly. Disturb an equilibrium and it responds by undoing the disturbance: adding reactant pushes it towards the products, and removing product as it forms does the same, because it tries to replace it. That is Le Châtelier's principle, and it is the most profitable industrial trick there is: it takes you from sixty per cent to ninety-five without touching the temperature or the catalyst.

Where this sits

Comes after
Reaction rate

Exercises from this rung

Generated by the app, from easiest to hardest

  1. When a reaction reaches equilibrium, what happens?

    • Both keep happening at the same rate
    • There is the same amount of everything
    • Everything stops
    • The reactants run out

    Why Nothing stops: the reaction keeps going both ways, just at the same rate, so the amounts stop changing. It is a dynamic stalemate, like walking down an up escalator. And equilibrium does not mean half and half: there can be ninety per cent on one side.

    easier

  2. You add more reactant to an equilibrium. Which way does it shift?

    • Towards the products
    • The equilibrium breaks for good
    • Towards the reactants
    • It does not move

    Why Towards the products. An equilibrium that is disturbed responds by undoing the disturbance: if there is excess reactant, it consumes it. It is called Le Châtelier's principle and it is plain common sense once you see that the reaction keeps running both ways.

    in between

  3. What does the equilibrium constant tell you?

    • How much energy it releases
    • How long it takes to get there
    • Whether the reaction is dangerous
    • Which way the equilibrium sits

    Why If it is large, at equilibrium there are mostly products; if small, mostly reactants. What it does not tell you is how long it takes to get there, which is the rate and is another matter: there are reactions with an enormous constant that take centuries, like diamond turning into graphite right now, very slowly.

    harder