Rates of Reaction

What are the necessary conditions for a dust explosion?

1. Any solid material that can burn in air 2. An atmosphere must contain sufficient oxygen to support combustion 3. A source of ignition.

What are the general properties of catalysts?

1. Catalysts are recovered chemically unchanged at the end of a reaction. 2. Catalysts tend to be specific; they may catalyse one reaction but have no effect on a similar reaction. 3. Biological catalysts, called enzymes, tend to be extremely specific. 4. Catalysts need only be present in small amounts; an increase in the amount of a catalyst does not significantly alter the rate of reaction. 5. For equilibrium reactions, catalysts help equilibrium to be achieved quicker. 6. The effect of a catalyst can be destroyed by substances called catalytic poisons.

What assumptions are the collision theory based on?

1. For a reaction to occur, the reacting particles must collide with each other. 2. A collision only results in the formation of products if a certain minimum energy is exceeded in the collision. This results in an effective collision.

What are the types of catalysis?

1. Homogeneous catalysis 2. Heterogeneous catalysis 3. Autocatalysis.

What are the theories of catalysis?

1. Intermediate formation theory 2. Surface adsorption theory.

What are the factors affecting rate of reaction?

1. Temperature 2. Particle size 3. Concentration 4. Nature of the reactants 5. Catalysts.

Describe how catalysts affect rate of reaction.

A catalyst works by reducing the activation energy needed for a reaction to occur.

Describe how catalytic converters work.

Exhaust fumes contain carbon monoxide (CO), nitrogen oxide (NO), nitrogen dioxide (NO2) and unburned hydrocarbons, which are all a major source of air pollution. A catalytic converter consists of a thin coating of platinum (Pt), palladium (Pd) and rhodium (Rh), all metal catalysts, on a metal 'honeycomb' inside a stainless steel casing. The 'honeycomb' inside of the catalytic converters has a high surface area so it increases the surface area of the catalysts.

Describe activation energy.

If a reaction has a large activation energy, it is slow as only a small fraction of the particles have enough energy to cause an effective collision. If a reaction has a small activation energy, it is fast as a larger fraction of particles have the necessary amount of energy for an effective collision to occur.

Describe how nature of reactants affects rate of reaction.

If the reactants in a chemical reaction are covalently bonded the reaction will be slow as their bonds have to be broken. If the reactants are ionically bonded the reaction will be faster as no bonds have to be broken. This is because reactions with covalent bonding have a higher activation energy because bonds have to be broken and formed again.

Describe how particle size affects rate of reaction.

In a reaction, the smaller the size of the particles the faster the reaction. This is because of the greater surface area of the particles, which increases the number of collisions and therefore increases the number of effective collisions.

Describe how temperature affects rate of reaction.

Increasing temperature in a chemical reaction increases the rate of the reaction. This is because the heat gives the particles more energy so there is a higher chance the particles will reach their activation energy causing an increase in the number of collisions and therefore an increase in the number of effective collisions.

Describe how concentration affects rate of reaction.

It has been found that increasing the concentration of reactants in a chemical reaction alters the rate of the reaction. Increasing the concentration, will increase the number of collisions and therefore increase the number of effective collisions.

What is homogeneous catalysis?

This is when both the reactants and the catalyst are in the same state; both liquids or both gases.

What is autocatalysis?

This is when one of the products of the reaction, catalyses the reaction. These reactions will start of slow until the catalyst is produced, and then it will speed up.

What is heterogeneous catalysis?

This is when reactants and the catalyst are in different states.

Describe surface adsorption theory.

This suggests that the reactants accumulate on the surface (adsorb) of the catalyst. This brings the particles closer together and increases the number of collisions and therefore increases the number of effective collisions. This theory explains most examples of heterogeneous catalysis. There are three main stages in a reaction according to this theory: 1. Adsorption. 2. Reaction. 3. Desorption.

Describe intermediate formation theory.

This theory suggests a catalyst works by forming an intermediate in the middle of the reaction and then forming a product.