(3.9-3.16) Rates of reaction

experiments, catalysts, reaction profiles

What does ‘rate of reaction’ refer to?

The speed at which reactant become products

Explain Particle Collision theory.

The rate of a reaction depends on:

• the collision frequency of particles

  • more collision = faster reaction

• the energy transferred / collision

  • particles must collide with activation energy

What is activation energy?

The minimum amount of energy needed for a reaction to occur

What are the factors affecting the rate of reaction?

surface area of solid

temperature

concentration of solution

pressure of gas

presence of a catalyst

How does temperature affect rate of reaction?

higher temp = faster rate

• higher temp = higher kinetic energy

• particles moves faster = collide more

• higher energy = successful collisions

How does concentration/pressure increase rate of reaction?

higher conc./pressure = faster rate

• more particles in given volume

• higher likelihood of collision

• higher likelihood of successful collision

How does surface area of a solid increase rate of reaction?

increased SA = faster rate

• greater SA exposed to other reactant

• higher rate of collision

• more frequent + successful collisions

What is a catalyst?

A substance that

speeds up the rate of reaction,

without being changed or used up in the process

How does a catalyst increase rate?

Decrease activation energy

by providing an alternative reaction pathway

with lower E_A

so, more particles reach minimum required energy

Describe the set up to investigate factors affecting rate of reaction.

(Precipitation reaction)

1. Set up a conical flask over a black cross.

2. Add acid to thiosulfate solution in the conical. Start timer.

3. Stop timer when X is obscured by ppt.

Measure temp by heating reactants

Measure concentration by diluting reactants

Measure catalyst by adding catalyst

Describe the set up to investigate factors affecting rate of reaction.

(Safe gas reaction)

1. Place conical flask on a mass balance

2. React acid and solid inside, plugging the top with cotton to stop spitting

3. Record the decrease in mass against time.

Describe the experiment to investigate SA effect on rate.

1. Connect gas syringe to conical flask.

2. React calcium carbonate chips with an acid.

3. Measure volume of gas given off in a fixed time.

4. Repeat with different sizes of marble chips.

Describe the experiment to investigate effect of a catalyst on rate.

1. Hydrogen peroxide in conical flash connected to gas syringe

2. Measure decomposition by recording gas given off at regular intervals.

3. Repeat with same vol/conc. but different catalysts:

   • manganese (IV) oxide

   • copper oxide

   • lead (II) oxide

Describe a reaction profile.

An energy level diagram with

• labelled rise for activation energy

• labelled ΔH