← Back to subjects
⭐ 0
IB Diploma Chemistry SL · Reactivity 2.2 & 2.3 — rate and extent of reaction
Mini-Lesson

How fast, how far — rate and equilibrium

This mini-lesson covers Reactivity 2.2 & 2.3: rate of reaction and collision theory, the factors that change rate, dynamic equilibrium, Kc and Le Chatelier's principle.

collision theorydynamic equilibriumLe Chatelier Reactivity 2 — how fast and how far reactions go

Work through each screen, answer the questions as you go (some are wordy, some are calculations) and collect ⭐ stars. Press Start when you're ready.

Reactivity 2.2

Collision theory

Reactions happen when particles collide with enough energy (≥ the activation energy) and the correct orientation. More frequent, more energetic successful collisions = faster rate.

Reactivity 2.2

Factors affecting rate

  • Concentration / pressure ↑ → more frequent collisions.
  • Surface area ↑ (powder) → more contact.
  • Temperature ↑ → particles faster and more have ≥ Ea.
  • Catalyst → provides a lower-Ea pathway (not used up).
Quick check

Speeding it up

?Which change does NOT increase the rate of a reaction between a solid and an acid?
Calculate

Temperature rule of thumb

1As a rule of thumb the rate roughly doubles for each 10 °C rise. By roughly what factor does the rate increase for a 30 °C rise?
×
Doubling three times: 2 × 2 × 2 = 2³.
Reactivity 2.3

Dynamic equilibrium

In a closed system a reversible reaction reaches dynamic equilibrium: the forward and reverse reactions continue at equal rates, so concentrations stay constant (but are not equal).

Reactivity 2.3

The equilibrium constant Kc

For aA + bB ⇌ cC + dD:

Kc = [C]ᶜ[D]ᵈ ÷ [A]ᵃ[B]ᵇproducts over reactants, each raised to its coefficient

A large Kc means products are favoured; a small Kc means reactants are favoured.

Calculate

Evaluate Kc

2For H₂ + I₂ ⇌ 2HI, at equilibrium [HI] = 0.80, [H₂] = 0.10, [I₂] = 0.10 mol dm⁻³. Calculate Kc.
Kc = [HI]² ÷ ([H₂][I₂]) = 0.80² ÷ (0.10 × 0.10).
Reactivity 2.3

Le Chatelier's principle

If a system at equilibrium is disturbed, it shifts to oppose the change:

  • ↑ reactant concentration → shifts toward products.
  • ↑ pressure → shifts toward the side with fewer gas moles.
  • ↑ temperature → shifts in the endothermic direction.

A catalyst speeds both directions equally — it does not move the position or change Kc.

Quick check

Predict the shift

?For N₂ + 3H₂ ⇌ 2NH₃, increasing the pressure shifts the equilibrium:
Quick check

What a catalyst does

?Adding a catalyst to a reaction at equilibrium:
Sort it

Which idea?

Tap a phrase, then the concept it belongs to.

💥 Collision theory

⚖️ Equilibrium feature

🔄 Le Chatelier response

Match it

Match change to effect

Tap an item on the left, then its match on the right.

Change
Effect
Recap

The big ideas to know

Rate: collisions with energy ≥ Eₐ and correct orientation; conc, SA, temp, catalyst

Dynamic equilibrium: closed system, equal forward/reverse rates

Kc: products over reactants to their coefficients; large Kc favours products

Le Chatelier: system shifts to oppose changes; catalyst changes neither position nor Kc

You've covered How fast, how far — rate and equilibrium for IB Diploma Chemistry SL. Press Finish to see your score.

🏆

Mini-lesson complete!

⭐⭐⭐

You've worked through How fast, how far — rate and equilibrium for IB Diploma Chemistry SL. 🎉

Your stars: 0 / 0

Next: test yourself in the Evaluate stage Confidence Quiz, then lock it in with Verify.

📣 Smashed it? Share your score

Challenge a mate to beat your stars, or show a parent how you got on.

→ Back to all subjects