Rate of Reactions

In general, how can reactions be triggered and their rate increased

• Collision of particles must occur at the right angles

• High frequency of effective collisions

• Sufficient energy i.e. activation energy

How can concentration of solution affect the rate of reaction?

1. Increased | decreased concentration of solution

2. Increased | decreased number of particles per unit volume of solution

3. Reactant particles collide more | less frequently

4. Frequency of effective collisions increases | decreases

How can pressure of gaseous reactant affect the rate of reaction

1. Increased | decreased pressure of gas

2. Increased | decreased number of particles per unit volume of gas

3. Reactant particles collide more | less frequently

4. Frequency of effective collisions increases | decreases

How can particle size of solid reactant affect the rate of reaction

1. Decreased | increased particle size of solid

2. Increased | decreased exposed surface area of solid in contact with other reactant particles

3. Reactant particles collide more | less frequently

4. Frequency of effective collisions increases | decreases

How can temperature affect the rate of reaction

1. Increased | decreased temperature of system

2. Increased | decreased kinetic energy of reactant particles

3. Increased | decreased speed of vibration

4. Increased | decreased number of reactant particles possessing energy ≥ activation energy

5. Reactant particles collide more | less frequently

6. Frequency of effective collisions increases | decreases

What is a catalyst?

A substance that increases the rate of chemical reaction without being changed at the end of the reaction

• Not used up during the reaction

• Physical appearance may change, but chemically the same

Some characteristics of catalysts (effect on yield, effect of impurities, selectiveness)

• Increases reaction rate but not the yielld

• Only able to catalyse certain reactions

• Impurities can poison them

How do catalysts affect rate of reaction?

1. Provides an alternative pathway of lower activation energy for the reaction to occur

   1. Some particles still use the original route

2. Due to alt. pathway, more reactant particles will have energy ≥ activation energy

3. Increases the frequency of collisions between particles

Examples of catalysts

• Iron (haber process)

• Al2O3 or SiO (cracking of hydrocarbons)

• Nickel (manufacturing margarine from vegetable oils)

• Platinum, palladium and rhodium (catalytic converters)