F322: Reaction Rate

Introduction

"The change in concentration of a reactant or a product in a given time".
E.g. Combustion = Fast reaction Rusting of Fe = Slow reaction
For most reactions:
-The rate is fastest at the start, the reactant concentration is at is highest.
-As the reaction proceeds, the rate decreases.
-When one of the reactants is used up, the rate becomes zero.
Factors affecting rate:
-Temperature
-Pressure
-Concentration
-Surface Area
-Catalyst
For chemical reactions to occur, particles must collide; with sufficient energy.
ACTIVATION ENERGY.
The molecules must also collide with the correct orientation.

1 of 8

Increasing concentration of a reactant will increase the rate of reaction:
-Number of particles in a given volume increases.
-Number of collisions will increase.
-Number of SUCCESSFUL collisions will increase.
-More reactions occur.

2 of 8

Increasing pressure will increase the rate because it effectively increases concentration.
Increase rate because:
-The particles are closer together.
-More frequent collisions.
-Number of successful collisions increases.
-More reactions will occur.

3 of 8

Must consider activation energy: "Energy required to start a reaction by breaking of bonds".
Increasing temperature increases rate because:
-Molecules move faster as they have more kinetic energy.
-Number of successful collisions occurs, as they have energy greater than activation energy.
-More reactions will occur.

4 of 8

We can show this on the Boltzmann distribution curve.

-The graph shifts to the right and the peak is lower.

5 of 8

"A catalyst speeds up a reaction without being consumed in the overall reaction".
They provide an alternative route for reaction to go through, with lower activation energy.
Increase rate because:
-Lower activation energy; so more molecules have sufficient energy.
-Number of successful collisions increase.
-More reactions will occur.

6 of 8

7 of 8

Used in industrial processes:
E.g. Fe in the Haber process to make NH3, Ziegler-Natta in production of polyethene, and Ni in hydrogenation of oils to make margarine.
They:
-Can be reused.
-They lower the activation energy, reducing energy and costs.
-They means less fossil fuels are needed.
-Better atom economy and less hazardous waste.
Enzymes are a biological homogenous catalyst, they are large protein molecules that are in the same phase as the reactants.
Industrially useful because:
-Lower temperature and pressure needed, so less energy costs.
-Produce single pure product, good atom economy.
-They are biogradable, so can be disposed of.

8 of 8