FACTORS AFFECTING RATES OF REACTIONS

TemperatureWhen temperature increases, the particles move faster causing more collisions & the reaction rate increases

Simulation

ConcentrationWhen concentration increases, there are more particles which mean more collisions so the reaction rate increases.

Simulation

PressureThere are 3 ways to change pressure: Change the volume (varies inversely with

pressure) Add more product or reactant Add an inert gas A decrease in volume causes an increase

in concentration which leads to an increase in reaction rate. An increase in pressure means an increased reaction rate.

Nature of ReactantsThe number & type of bonds that are required to be created & broken in a chemical reaction affects the rate of reaction.The fewer amounts of the bonds needing to be broken, the faster the rate.Ionic compounds have weaker bonds than covalent compounds, so they have a faster reaction rate.

Surface AreaIncreased surface area increases the reaction rate BUT the phase the reaction is in affects the reaction rate as well. Solids are the slowest since the reactants cannot move freely. Gases & liquids are faster because the particles can move more freely. Ions in solution (aqueous) have the fastest rate since they can move the most. Homogenous and heterogeneous reactions come into affect here.

EFFECT OF SURFACE AREA ON RATE OF REACTION

Any reaction involving a solid can only take place at the surface of the solid.

If the solid is split into several pieces, the surface area increases. What effect will this have on rate of reaction?

The smaller the pieces, the larger the surface area. This means more collisions and a greater chance of reaction.

This means that there is an increased area for the reactant particles to collide with.

low surface area high surface area

SURFACE AREA AND PARTICLE COLLISIONS

THE EFFECT OF SURFACE AREA ON RATE

reaction (time)

en

erg

y (

kJ)

WHAT ARE CATALYSTS?Catalysts are substances that change the rate of a reaction without being used up in the reaction.

Catalysts never produce more product – they just produce the same amount more quickly.

Different catalysts work in different ways, but most lower the reaction’s activation energy (Ea).

Ea withcatalyst

Ea withoutcatalyst

Catalysts & InhibitorsCatalysts speed up reactions by lowering the activation energy. Inhibitors are the opposite.

MULTIPLE-CHOICE QUIZ