The change in concentration of the reactants or products

with time

RATE OF REACTION

OBJECTIVES

At the end of this presentation, you should be able to:• define rate of reaction• identify at least four factors which affect the rate of a

chemical reaction • explain how the factors cited affect the rate of

reaction• illustrate graphically how a catalyst alters the rate of

reaction• describe two ways that reaction rate can be

measured.

COLLISION THEORY

For a reaction to occur the particles (atoms, molecules) have to collide with each other.The more frequently they collide, the faster the rate of reaction.For a reaction to occur the particles must have a minimum amount of energy. This is called the ACTIVATION ENERGY.

FACTORS AFFECTING THE RATE OF REACTION

Concentration

Temperature

Surface Area

Pressure

Catalyst

EFFECT OF CONCENTRATION

• In a concentrated solution, there are more solute particles per unit volume. Increasing the concentration, increases the probability of a collision between the reactant particles since there are more of them in the same volume.

• Hence, the greater the concentration, the greater the frequency of collision and the faster the rate of reaction.

EFFECT OF TEMPERATURE

• As the temperature increases, the frequency of collision increases and more particles gain the activation energy necessary for the reaction to take place.

• Hence, as temperature increases, the faster the rate of reaction.

EFFECT OF SURFACE AREA

• If a solid reactant is broken down into smaller pieces the rate of reaction increases.

• The particles now have a greater surface area compared to larger pieces of the solid.

• Hence, there is more chance of a reactant particle colliding with the solid surface

• As the frequency of collision increases, the faster the rate of reaction.

EFFECT OF PRESSURE

Pressure is only considered when gases are involved. Look at the diagrams below and explain how the rate is affected when there is an increase in pressure.

EFFECT OF CATALYST

• A catalyst speeds up the rate of a chemical reaction by providing an alternate pathway of lower activation energy.

• Since the activation energy is reduced, more particles will have enough energy to result in a reaction.

EFFECT OF CATALYST

• Observe the energy profile diagram for an endothermic reaction with and without a catalyst.

• Now draw the energy profile diagram for an exothermic diagram with and without a catalyst.

MEASURING THE RATE OF A REACTION

Two common ways:• Measuring how fast the products are being

produced.• Measuring how fast the reactants are being

used up.

Measuring how fast the products are being produced.

Visit the following link for more information:http://www.thestudentroom.co.uk/showthread.php?t=942653

Measuring how fast the reactants are being used up

Visit the following link for information:• http://johnwest.edublogs.org/2009/08/18/ncea-level-2-chemistry-rates-o

f-reaction-strong-and-weak-acids/

RATE OF REACTION GRAPHS (Measuring how fast the products are being produced.)

RATE OF REACTION GRAPHS (Measuring how fast the reactants are being used up)

1. Can you account for the shape of this graph?2. How would the graph look if the same experiment was carried out at a

higher temperature? Discuss your answer with your teacher.