Rates of Reaction

#folder

See Chemical Reactions

Conditions For Chemical Reactions

List

  • Molecules must collide
  • Molecules must collide with sufficient energy (must reach activation energy)
  • Molecules must collide in the correct orientation

Catalyst

Definition

A catalyst decreases the amount of energy needed to cause a reaction by providing a reaction path with lower activation energy

A catalyst only increases the rate of the reaction. It is not altered by the reaction.

Catalysts can be homogeneous or heterogeneous.

Factors Affecting Reaction Rate

List

  1. Concentration of reactants
    • High concentration = more collisions
  2. Reaction temperature
    • Higher temperature -> more reactants with sufficient energy
  3. Presence of catalysts
  4. The physical nature of the reactants
    • Most reactions occur in gas or liquid phase because reacting particles have greater freedom of movement and are more likely to collide

Example

The chemical equation for the reaction of iron () metal with hydrochloric acid () is:

Will the rate of this reaction increase, decrease, or remain the same when:

  1. The temperature is increased
    • Increase (more energy)
  2. The solution is stirred
    • Increase (more collisions)
  3. The concentration of the acid is increased
    • Increase (more collisions)
  4. The iron is ground into a powder?
    • Increase (more collisions)

Measuring Reaction Rates

Info

We measure reaction rate as rate of change of concentration with units

(see mole)

We denote the concentration of a molecule as .

Formula

Consider the reaction .

  • When , we have
  • When , we have , where is some unknown concentration
Formula

We have (derivative), so

where is the rate of reaction of and is the coefficient of .

  • If it's a product, reaction rate of change will be positive (production)
  • If it's a reactant, the rate will be negative (consumption)
Example

For the reaction

the rate of reaction if . What is the rate of change of concentration? What about .

solution