2.3 Rates of Reaction ⏰️

Measuring rate of reaction

amount of product formed/ reactant lost over period of time

Rate of reaction equation

1/time

Rate of reaction units

s^-1

Rate of reaction graph

faster reactions have steeper gradients and plateau sooner (greater rate of reaction)

Measuring rate of reaction metal + acid (product method)

volume of hydrogen gas given off using gas syringe over time with stopwatch

Mg + 2HCl →

MgCl₂ + H₂

Measuring rate of reaction calcium carbonate (marble chips) + acid (reactant method)

loss in mass of mixture (co₂) using balance over time with stopwatch

CaCO₃ + 2HCl →

CaCl₂ + CO2 + H2O

Measuring rate of reaction forming a precipitate (sodium thiosulfate)

time taken for solution to go from transparent to opaque

Collision theory

particles must collide to have reaction, requiring enough energy or they will just bounce apart

How is collision theory linked to rate of reaction

more successful collisions means faster rate of reaction

Activation energy

minimum energy required for a reaction to occur

Factors affecting rate of reaction

• surface area/ size

• concentration

• temperature

• catalyst

Effect of surface area on rate of reaction

• more particles exposed to reactant

• collide more often, more successful collision per unit time

• rate of reaction increases

How to increase surface area

using smaller particles e.g cutting/ powder

Effect of concentration on rate of reaction

• more reactant particles

• collide more often, more successful collision per unit time

• rate of reaction increases

Effect of temperature on rate of reaction

• particles have more kinetic energy, moving quicker

• collide more often, more successful collision per unit time

• rate of reaction increases

Catalyst

substance that increases the rate of a chemical reaction without being used up

Effect of catalyst on rate of reaction

• provides alternative reaction pathway of lower activation energy

• more successful collision per unit time

• rate of reaction increases

Catalyst in decomposition of hydrogen peroxide

manganese(IV) oxide

Using manganese(IV) oxide

black solid, removed from mixture by filtration

2H₂O_2(aq) →

2H2O + O2