The Equilibrium Constant Kc · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Putting a number on equilibrium

Science · Chemistry · ages 16-18
Name ______________________   Date ____________

  1. A Kc of a billion means...

    • The mixture sits almost all as products
    • Barely anything reacts
    • The reaction runs very fast

  2. The expression for Kc is...

    • The sum of all concentrations
    • Reactants over products
    • Products over reactants, each to its balancing power

  3. A large Kc means a fast reaction.

    Circle one:   True   False

  4. 0.4 mol sits in a 2 cubic decimetre vessel. What is its concentration?

    • 0.8 mol per cubic decimetre
    • 0.2 mol per cubic decimetre
    • 0.4 mol per cubic decimetre

  5. Using the lesson example, Kc is 0.1 times 0.1 over 0.2 times 0.2. Type the number.

    Answer: ______________

  6. Why do Kc units change between equations?

    • Units are decoration
    • Kc always carries the same units
    • They come from the expression, which differs each time

  7. Suppose an esterification gives Kc as 4. What does the size say about the yield?

    • Nothing, Kc only gives speed
    • Products are favoured, so a decent yield sits at equilibrium
    • No reaction happens at all

  8. For A plus B giving C, a student slots moles straight in, skipping the volume. What breaks?

    • Nothing changes at all
    • The value shifts by the volume factor and the units come out wrong
    • Only the sign flips
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Answer key

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

Putting a number on equilibrium W1-mt_3G8b6Hyz3u-s1

  1. The mixture sits almost all as products · Huge Kc means the position lies far to the product side.
  2. Products over reactants, each to its balancing power · Products sit on top, each raised to its balancing number.
  3. False · Kc fixes the final position and says nothing about speed.
  4. 0.2 mol per cubic decimetre · Divide moles by the volume: 0.4 over 2.
  5. 0.25 · Top gives 0.01 and bottom gives 0.04.
  6. They come from the expression, which differs each time · Each expression leaves a different trail of units.
  7. Products are favoured, so a decent yield sits at equilibrium · Above one leans to products, so the yield is respectable.
  8. The value shifts by the volume factor and the units come out wrong · Each missed division leaves stray volume in the value and units.
Worksheet · LightMySky