rate of reaction

Rate of reaction

change in concentration per unit time of any one reactant or product.

Instantaneous Rate

The rate of reaction at any one particular time during the reaction

What is collision theory

For a chemical reaction to occur, particles must collide.

This collision must have enough energy to cause a chemical reaction.

Effective Collision

one which results in a reaction

Activation Energy

minimum combined energy of colliding particles for reaction to take place

Factors affecting rate of reaction

1. Nature of reactants

2. particle size

3. concentration

4. temperature

5. catalyst

Nature of Reactants

Covalent substances

• bonds need to be broken.

• energy is needed to break these bonds so it takes longer.

  Ionic bonds

• faster, no bonds need to be broken

Particle Size

smaller particles react faster as there is a large surface area for the particles to collide. Increase number of collision means more chance of an effective collision

Reducing particle size increases the rate of reaction.

Concentration

at higher concentrations, there are more particles. More particles means more chance of a collision meaning more effective collisions.

Increasing the concentration increases the rate of reaction.

Temperature

at higher temperatures, particles move faster.

The faster particles move with more energy, the more chance there is for a collision, leading to a high chance of effective collisions.

Increasing the temperature increases the rate of reaction.

Catalyst

a substance that alters the rate of reaction without being used up in the process

what is a negative catalyst or a inhibitor

one that slows down a reaction

biological enzyme

amylase

Properties of a catalyst

• used in small amounts

• unchanged at the end of a reaction

• can be destroyed by a catalytic poison

Types of Catalysts

Homogenous

Heterogenous

Autocatalysis

Homogenous

the reactant and catalyst are in the same phase

Heterogenous

the reactant and catalyst are in different phases

Autocatalysis

one of the products of the reaction catalyses the reaction

Mechanisms of Catalysts

• Intermediate compound

• Surface adsorption

Intermediate compound

Catalyst works by forming an intermediate compound which is present for a short period of time.

formula for intermediate compound

W (reactant) + C (catalyst) -> WC

WC + X (reactant) -> Y+Z+C

adsorption

the accumulation of a substance on a surface

surface adsorption theory

1) Reactants are adsorbed onto the surface of the catalyst, forming temporary bonds

2) Reactants are close together at high concentrations on the surface - more likely to collide with each other

3) The products diffuse away from the surface of the catalyst

Catalytic converters

A catalytic converter is fitted into the exhaust of a car and converts these harmful gases into less harmful gases.

What are the harmful gases

carbon monoxide

nitrogen monoxide

nitrogen dioxide

Catalytic converters are made of

Rhodium

Palladium

Platinum

Reaction profile diagram

A graph which shows the change in energy of a chemical reaction with time as the reaction progresses

endothermic reaction

A reaction that takes in energy in the form of heat

exothermic reaction

A reaction that releases energy in the form of heat