BIG Idea of Unit
 Chemicals react together in predictable ways
 How to name ionic and covalent compounds
 How to balance chemical equations
 How to identify the common types of reactions
 TODAY.. What factors affect the rate at which these
reactions occur?
Outline
 Rate of reaction
 Collision Model
 4 main Factors & Investigation:
 Temperature
 Concentration
 Surface Area
 Catalyst
Rate of Reaction
 Rate of reaction = Quantity of product produced
Time Required
 Chemical reactions occur at different rates
 Today we will consider some of the key factors that
influence the rate of reaction
Collision Model
 The rate of reaction is effected by the number of
collisions of reactant molecules
 In order for collisions to be effective, the molecules
must collide with sufficient energy
 Molecules must also collide with proper orientation
Collision Model
 Factors we will examine that influence the reaction by:
 Increasing the number of collisions OR
 Increasing the fraction of collisions that will be
successful
INVESTIGATION
How does the temperature affect rate of reaction?
How does the temperature of water affect the rate at which an
Alka Seltzer tablet dissolves?
Reaction: NaHCO3 (s) + H2O (l) → NaOH (s) + H2O (l) + CO2
(g)
Predictions?
Observations: On observation Handout
Explanation: To follow!
Temperature
 Increases energy of particles due to increase of
temperature
 Increase speed of particles and there are more
successful collisions because molecules to contact one
another more readily and with harder force
 Therefore increased temperature = increased rate
of reaction
How does the concentration of a solution affect the rate of
reaction?
How will different concentrations (strengths) of hydrochloric
acid dissolve zinc?
Reaction: Zn (s) + 2HCl (l) → ZnCl2 (aq)+ H2 (g)
Predictions?
Observation: Fill out on handout provided
Explanation: to follow!
Concentration
 Concentration: the amount of a substance (solute)
present in a given volume of solution
 “Packing” in more molecules increases the number of
collisions
 Therefore a more concentrated solution =
increased rate of reaction
How does surface area affect the rate of reaction?
How does surface area affect the rate of reaction of chalk with
hydrochloric acid? (Solid chalk vs. powder chalk)
Reaction: CaCO3 (s) + 2HCl (aq) → CaCl2 (aq) + CO2 (g) + H2O
(l)
Predictions:
Observations: on handout provided.
Explanation: to follow!
Surface Area
 If particles are in the same phase (liquid/liquid or
gas/gas) then it is easy for them to mix with each other
 This gives particles maximum opportunity to collide
 But if one of the reactants is a solid, the reaction can
only take place on the SURFACE of the solid
 The smaller the size of the particles, the greater the
surface area that the reaction can take place in
 Therefore, smaller surface area = increased rate of
reaction
How does the addition of a catalyst effect the rate of reaction?
Which solution will act as a catalyst effect the decomposition of
hydrogen peroxide?
Reaction: 2H2O2 (l) → 2H2O (l) + O2 (g)
Predictions: ??
Observations: On handout provided
Explanation: to follow!!
Catalyst
 Substance that enhances the rate of chemical
reaction without being consumed itself
 They decrease the amount of collision energy needed
to break bonds and form new ones making the
fraction of successful collisions more effective
 Catalysts provide an easier path for reactions to follow
 Note: An enzyme is a protein compound that acts as a
biological catalyst
 Therefore presence of catalyst = increased rate of
reaction
Reminders:
 Lab tomorrow
 Quiz Friday on:
 Factors that Effect the Rate of Reaction
 Types of Chemical reactions


Classifying types of chemical reactions
Balancing chemical reactions