Rates of Reaction & Catalysts
The rate of a chemical reaction measures how fast reactants are converted into products. Under collision theory, chemical reactions only occur when particles collide with energy greater than or equal to the activation energy; changing temperature, concentration, gas pressure, surface area, or adding a catalyst alters collision frequency or energy.
- Rate of Reaction
- The change in concentration of a reactant or product per unit time.
- Activation Energy
- The minimum amount of energy that particles must have to react when they collide.
- Catalyst
- A substance that increases the rate of a chemical reaction without undergoing any permanent chemical change itself.
Rates of Reaction & Catalysts: Reaction Profile (ΔH & E_a) + Le Chatelier Yield Simulator
Toggle a catalyst on the enthalpy profile diagram or adjust temperature and pressure to see how dynamic equilibrium shifts.
Modelled on N₂(g) + 3H₂(g) ⇌ 2NH₃(g) (ΔH = −92 kJ/mol) (4 moles gas → 2 moles gas):
Higher pressure shifts equilibrium to the side with fewer gas moles (right, 4 → 2). Lower temperature favours the exothermic forward reaction.
Key Concepts & Exam Definitions (5)
- Rate of Reaction
- The change in concentration of a reactant or product per unit time.
- Activation Energy
- The minimum amount of energy that particles must have to react when they collide.
- Catalyst
- A substance that increases the rate of a chemical reaction without undergoing any permanent chemical change itself.
- Surface Area
- The total area of the surface of a solid object. Increasing it speeds up reaction rates for solids.
- Collision Theory
- A model that explains reaction rates based on successful collisions between reactant particles.
Quick-Fire Flashcards (5)
Click any card to check the answer, then mark it as Known to track your progress.
What happens to the rate of reaction if concentration is increased?
How does temperature affect the rate of reaction?
What is the formula for calculating rate of reaction?
Do catalysts get used up in a reaction?
Why does a powder react faster than a lump of the same mass?
Exam-Style Questions & Mark Schemes (3)
Write or think through your answer first, then click Check Mark Scheme to see the exact points examiners award marks for.
- Q1
Explain, in terms of particles, why increasing the temperature increases the rate of reaction.
Click “Check Mark Scheme” to compare your answer, Particles gain more kinetic energy, moving faster and colliding more frequently. More collisions have energy greater than the activation energy, so a higher proportion of collisions are successful.
- Q2
A reaction produces 40 cm3 of gas in 20 seconds. Calculate the mean rate of reaction.
Click “Check Mark Scheme” to compare your answer, 40 / 20 = 2 cm3/s.
- Q3
Why are catalysts important in industry?
Click “Check Mark Scheme” to compare your answer, They reduce the energy required for reactions, which saves money on energy costs and reduces environmental impact, and they speed up production.
Common Exam Questions (3)
How can you measure the rate of a reaction?
Measure the rate of a reaction by recording either the mass or volume of a product formed or the mass of a reactant used up over time: Rate of reaction = amount of reactant used or product formed ÷ time.
What is collision theory?
Collision theory states that chemical reactions can only occur when reacting particles collide with each other with sufficient energy, known as the activation energy (Ea).
How do catalysts work?
A catalyst increases the rate of a chemical reaction without being chemically changed or used up by providing an alternative reaction pathway with a lower activation energy, so a higher proportion of collisions are successful.
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Related study guides
Acids, Bases & pH
Aqueous solutions are classified as acidic, neutral, or alkaline using the pH scale from 0 to 14. In water, acids ionise to release hydrogen ions (H⁺) and alkalis release hydroxide ions (OH⁻); when an acid reacts with a base or alkali, neutralisation occurs to form a salt and water.
Moles, Relative Formula Mass & Calculations
Quantitative chemistry uses relative formula masses (Mr) and the mole concept to calculate reacting masses, gas volumes, and solution concentrations. Applying the core relationship moles = mass ÷ Mr allows you to determine limiting reactants, percentage yields, and titration concentrations.