Reaction rate

• The?rate of a reaction?is the speed at which a chemical reaction takes place and has units?mol dm-3?s-1
• The rate of a reaction can be calculated by:

Worked example: Calculating the rate of reaction

Answer

• Step 1:?Calculate the amount of ethyl ethanoate formed in mol

= 0.0005 mol

• Step 2:?Calculate the volume of the reaction mixture in dm3

400 cm³?= 0.400 dm³

• Step 3:?Calculate the concentration change of product formed

= 0.00125 mol dm^-3

• Step 4:?Calculate the time in seconds

1.0 min = 60.0 s

• Step 5:?Use the equation to calculate the rate

= 2.08 x 10^-5?mol dm^-3?s^-1

Collision theory

• The?collision theory?states that for a chemical reaction to take place the particles need to?collide?with each other in the correct?orientation?and with enough?energy
• The minimum energy that colliding particles must have for a collision to be?successful?and a reaction to take place is called the?activation energy?(Ea)

Collision theory table

• An?ineffective collision?is when particles collide in the wrong orientation or when they don’t have enough energy and?bounce off?each other without causing a chemical reaction

(a) shows an ineffective collision due to the particles not having enough energy whereas (b) shows an effective collision where the particles have the correct orientation and enough energy for a chemical reaction to take place

Increase in reaction rate

• The?collision frequency?is the number of collisions per unit time
• When more collision per unit time take place, the number of particles with energy greater than the?Ea?increases
• This causes an?increase?in?rate of reaction
• A?catalyst?is a substance that?increases?the?rate of reaction?without taking part in the chemical reaction by providing the particles an alternative mechanism with a lower activation energy

Diagram shows that a catalyst increases the rate of a reaction by providing an alternative pathway which has a lower activation energy