Reversible Reactions, Dynamic Equilibrium and Le Chatelier · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

The standstill that keeps moving

Science · Matter & Materials · ages 15-16
Name ______________________   Date ____________

  1. Why must an equilibrium system stay closed?

    • Closed flasks keep the light out
    • Open flasks let gases escape and break the balance
    • Open flasks cool the mixture down

  2. What is still happening at dynamic equilibrium?

    • All reactions have stopped completely
    • Only the forward reaction keeps going
    • Forward and reverse reactions run at equal rates

  3. In the copper sulfate change, heating one way is endothermic and the reverse is exothermic.

    Circle one:   True   False

  4. Higher pressure is applied to N2 + 3H2 going to 2NH3. What happens to ammonia yield?

    • It rises, since that side holds fewer gas molecules
    • It falls, since gases compress
    • It stays fixed whatever the pressure

  5. More hydrogen is pumped into the Haber mixture at equilibrium. What shifts?

    • It makes more nitrogen instead
    • Nothing changes at all
    • It makes more ammonia to use up the extra

  6. The best equilibrium yield needs cold, yet the plant runs warm. Why?

    • Heat melts the iron catalyst
    • Cold would slow the rate until output barely pays
    • Cold stops only the reverse reaction

  7. An iron catalyst is added to the Haber mixture. What changes?

    • The ammonia yield rises at equilibrium
    • Equilibrium arrives faster with the same final split
    • The pressure needed drops to normal air

  8. An exothermic equilibrium is heated. Which way does it shift?

    • Back towards reactants, favouring the endothermic way
    • Towards products to release more heat
    • It cannot shift once equilibrium is reached
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Answer key

For grown-ups. Fold this page away before handing over the rest.

The standstill that keeps moving W1-mt_Zas-V3kTiR-s1

  1. Open flasks let gases escape and break the balance · Escaping gas drains one side, so the rates can never settle equal.
  2. Forward and reverse reactions run at equal rates · Equal rates keep concentrations frozen while molecules keep swapping.
  3. True · Driving water off takes heat in, and wetting the powder gives it back out.
  4. It rises, since that side holds fewer gas molecules · Pressure favours the side with fewer gas molecules, which is two against four.
  5. It makes more ammonia to use up the extra · The system opposes the added reactant by turning it into product.
  6. Cold would slow the rate until output barely pays · Cold gives yield on paper but crawls, so warmth trades some yield for speed.
  7. Equilibrium arrives faster with the same final split · Catalysts hurry both directions equally, so arrival quickens but position holds.
  8. Back towards reactants, favouring the endothermic way · The system opposes heating by favouring the direction that takes heat in.
Worksheet · LightMySky