What is the rate of reaction in the context of chemical equilibrium?

The rate of reaction refers to the speed at which reactants are converted into products in a chemical reaction. In the context of chemical equilibrium, it is the point at which the rate of the forward reaction equals the rate of the reverse reaction, resulting in no net change in the concentrations of reactants and products over time.

How can temperature affect the rate of reaction?

Temperature can significantly affect the rate of reaction. Generally, increasing the temperature increases the kinetic energy of the molecules, leading to more frequent and energetic collisions. This typically results in a faster reaction rate. Conversely, lowering the temperature usually decreases the reaction rate. This concept is crucial in the IB MYP Science curriculum when studying chemical kinetics.

What role do catalysts play in the rate of reaction?

Catalysts are substances that increase the rate of a chemical reaction without being consumed in the process. They work by providing an alternative reaction pathway with a lower activation energy, allowing more reactant molecules to successfully collide and react. This is an important concept in understanding how reactions can be controlled and is often explored in IB MYP Science classes.

How does concentration affect the rate of reaction?

The concentration of reactants can affect the rate of reaction. A higher concentration means more reactant particles are present in a given volume, leading to an increased likelihood of collisions and, therefore, a faster reaction rate. This principle is fundamental in studying reaction rates and is a key topic in the IB MYP Science curriculum.

Why is the rate of reaction important in industrial processes?

The rate of reaction is crucial in industrial processes because it determines the efficiency and cost-effectiveness of chemical production. Faster reaction rates can lead to higher yields in shorter times, reducing energy consumption and costs. Understanding and controlling reaction rates is essential for optimizing industrial chemical processes, a concept that is often discussed in the context of real-world applications in the IB MYP Science program.

Why is "Saying a catalyst is 'used up' or 'becomes part of the product'." a common mistake in Rate of Reaction?

Why it happens: Catalysts seem to disappear in some demonstrations. How to avoid it: A catalyst takes part in the reaction but is regenerated. After the reaction, you can in principle recover the same mass.

Why is "Explaining the temperature effect only by 'particles move faster'." a common mistake in Rate of Reaction?

Why it happens: It's true but incomplete. How to avoid it: Full marks need BOTH: faster collisions AND more collisions with energy ≥ Ea. Mention both.

Why is "Confusing 'surface area' with the size of the solid." a common mistake in Rate of Reaction?

Why it happens: A bigger lump can SEEM to have more surface. How to avoid it: A finely-powdered solid has a HUGE total surface area for the same mass. Smaller pieces = larger total surface.

Chemical equilibriumIB MYP Sciences (Years 1-5)

Rate of Reaction

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Rate of Reaction — IB MYP Sciences: factors, collision theory and measuring how fast a reaction happens

Why does a flame burn fast but rust take years? This MYP Sciences note covers the four factors that change reaction rate — concentration, temperature, surface area and catalysts — and the collision theory that explains them all.

What you’ll learn

Mapped to the IB MYP Sciences subject guide (2026 onwards).

MYP Sciences A — State the four factors that change reaction rate.
MYP Sciences A — Use collision theory to explain each factor.
MYP Sciences A — Define a catalyst and describe its action.
MYP Sciences B — Plan a rate-of-reaction investigation, including a variable, control and method of measurement.
MYP Sciences C — Read a rate-vs-time graph and identify changes in slope.

Collision theory — why ANY reaction has a rate

For a reaction, particles must collide with enough energy AND the right orientation.

Chemical reactions need particles to MEET. Collision theory says a reaction only happens when:

Particles collide.
They have enough energy to break the existing bonds (the activation energy, Ea).
They are in the right orientation (the reactive parts of the molecules meeting).

If any of these is missing, particles just bounce off each other unchanged. Anything that makes successful collisions MORE FREQUENT speeds up the reaction; anything that makes them LESS FREQUENT slows it.

A reaction profile: particles must climb the activation energy hump for the reaction to proceed.

Reactions need: collisions + activation energy + right orientation.
Activation energy Ea = minimum energy for a successful collision.
More frequent + more energetic + correct collisions = faster.

Four factors that change rate

Concentration, temperature, surface area, catalysts.

Concentration. More particles in the same volume → more chances for collisions per second → faster. Doubling concentration usually about doubles rate.

Temperature. Heating particles makes them move faster (more frequent collisions) AND gives them more energy (more collisions exceed Ea). A 10 °C rise often roughly doubles the rate.

Surface area. A solid only reacts at its surface. Cutting a lump into powder hugely increases the surface exposed to the other reactant → faster. (This is also why dust explosions happen — fine flour, sawdust or coal dust react VERY rapidly.)

Catalyst. A catalyst speeds up a reaction without being used up. It works by providing an ALTERNATIVE reaction pathway with a LOWER activation energy — more collisions are now successful.

A catalyst provides a different pathway with a lower activation energy.

Higher concentration → more collisions → faster.
Higher temperature → more frequent + more energetic collisions → faster.
Larger surface area → more particles exposed → faster.
Catalyst → lower Ea → more successful collisions → faster.

Measuring rate in the lab

Track a quantity that changes during the reaction.

Three common ways to measure rate:

Mass loss (if a gas is produced and allowed to escape). Place the reaction flask on a balance and record mass every 30 s. The rate is the slope of mass-against-time.
Gas volume (if a gas is collected over water or in a syringe). Measure how the gas volume grows with time.
Colour change / cloudiness. Time how long it takes for a cross under the flask to become invisible (e.g. Na₂S₂O₃ + HCl → S precipitate).

Typical investigation:

Independent variable: ONE of the four factors.
Dependent variable: gas volume / mass / time-for-cross-to-disappear.
Controls: same volume, same other concentrations, same temperature (except when temperature IS the variable), same surface area.

The reaction is FASTEST at the start (steepest gradient on a rate graph) because reactant concentrations are highest. It slows as reactants are used up.

Measure mass loss, gas volume or colour/cloudiness change.
Plot quantity vs time; the gradient = rate.
Rate is fastest at start; decreases as reactants are consumed.

How it’s examined

Criterion A and C dominate this subtopic. Criterion C exam-style items present a rate graph and ask you to compare gradients or identify a factor that has changed. Criterion B is the 'plan an investigation' criterion — covered in school IAs.

Sources: IB MYP Sciences guide (IBO, official subject guide). Last reviewed 2026-05-25.

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Step-by-step worked examples — Rate of Reaction

Step-by-step solutions to past-paper-style questions on rate of reaction, written exactly the way a tutor would explain them at the board.

1Why heating speeds up a reaction
Building confidence• temperature
Question
Use collision theory to explain why heating a reaction mixture from 20 °C to 40 °C usually about doubles the rate.
Step-by-step solution
1. Step 1
  At higher temperature, particles have more kinetic energy and move faster.
2. Step 2
  More frequent collisions: more particles meet per second.
3. Step 3
  MORE of those collisions have enough energy to exceed the activation energy — a much bigger fraction is now successful.
Answer
Particles move faster (more frequent collisions) AND more collisions have ≥ Ea (more successful collisions). Both effects increase the rate.
2How a catalyst speeds up reaction
Building confidence• catalyst
Question
Explain how a catalyst speeds up a chemical reaction without being used up.
Step-by-step solution
1. Step 1
  A catalyst provides an alternative reaction pathway with a LOWER activation energy.
2. Step 2
  More particles now have energy ≥ the new lower Ea, so more collisions are successful.
3. Step 3
  The catalyst takes part in the reaction but is regenerated at the end — so it is not consumed overall.
Answer
Provides a lower-Ea pathway, so more collisions are successful. The catalyst itself is regenerated and not consumed.
3Reading a rate graph
Stretch• graph reading
Question
A graph plots volume of gas produced (cm³) against time (s). The curve is steep at the start, becomes less steep, and eventually flattens. Explain.
Step-by-step solution
1. Step 1
  Steep slope at start = fast rate. Reactant concentration is highest, so most collisions happen.
2. Step 2
  As reactants are used up, concentration falls → fewer collisions per second → rate decreases.
3. Step 3
  Eventually the reaction stops (one reactant exhausted) — graph flattens.
Answer
Steep start: high reactant concentration → fast. Slope decreases as reactants are consumed. Flat at end: reaction stopped (limiting reactant used up).

Key Formulae — Rate of Reaction

The formulae you need to memorise for rate of reaction on the IB MYP Sciences paper, with every variable defined in plain English and a note on when to use it.

Average rate of reaction
$rate = change in quantity / time$
$change in quantity$
Δ mass (g), Δ gas volume (cm³), etc.
$time$
seconds (s)
When to use
To convert experimental measurements into a numerical rate.

Key Definitions and Keywords — Rate of Reaction

Definitions to memorise and the exact keywords mark schemes credit for rate of reaction answers — sharpened from recent examiner reports for the 2026 IB MYP Sciences sitting.

Rate of reaction
Examiner keyword
How much product is formed (or reactant used up) per unit time.
Collision theory
Examiner keyword
Particles must collide with sufficient energy and correct orientation for a reaction to occur.
Activation energy (Ea)
Examiner keyword
The minimum energy that colliding particles must have for a reaction to take place.
Catalyst
Examiner keyword
A substance that speeds up a chemical reaction without itself being used up; provides a lower-Ea pathway.
Surface area
Area of solid exposed to a reactant. Smaller pieces = larger total surface area = faster rate.

Common Mistakes and Misconceptions — Rate of Reaction

The traps other students keep falling into on rate of reaction questions — taken from recent IB MYP Sciences examiner reports and mark schemes — and how to avoid them.

✕Saying a catalyst is 'used up' or 'becomes part of the product'.
Why it happens
Catalysts seem to disappear in some demonstrations.
How to avoid it
A catalyst takes part in the reaction but is regenerated. After the reaction, you can in principle recover the same mass.
✕Explaining the temperature effect only by 'particles move faster'.
Why it happens
It's true but incomplete.
How to avoid it
Full marks need BOTH: faster collisions AND more collisions with energy ≥ Ea. Mention both.
✕Confusing 'surface area' with the size of the solid.
Why it happens
A bigger lump can SEEM to have more surface.
How to avoid it
A finely-powdered solid has a HUGE total surface area for the same mass. Smaller pieces = larger total surface.

Practice questions

Exam-style questions with step-by-step worked solutions. Try one before checking the method.

Past paper style quiz

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Rate of Reaction — frequently asked questions

The things students keep getting wrong in this sub-topic, answered.

Rate of Reaction

Short Study Notes in the form of Slides

Short Study Notes — Rate of Reaction

Detailed Notes

What you’ll learn

How it’s examined

1Why heating speeds up a reaction

2How a catalyst speeds up reaction

3Reading a rate graph

Average rate of reaction

Rate of reaction

Collision theory

Activation energy (Ea)

Catalyst

Surface area

✕Saying a catalyst is 'used up' or 'becomes part of the product'.

✕Explaining the temperature effect only by 'particles move faster'.

✕Confusing 'surface area' with the size of the solid.

Practice questions

Past paper style quiz

Assess your understanding

Rate of Reaction — frequently asked questions