Section 2: Reaction Rates Collision Theory 5 Factors Affecting Rates

A. Rates Rate: measure of how fast any change happens over time.

reactants  products A. Rates Reaction Rate: change in concentration of reactants and products over time. (tell how fast a reaction is going) Example: TNT & leaves changing reactants  products get consumed get formed Rate is like speed (distance changes over time). TNT explosion is immediate, leaves change color happens gradually

A. Rates more reactants more products reactants products

B. Collision Theory Ineffective Collision Effective Collision

Activation Energy B. Collision Theory For rxn to occur, collision must have: proper orientation (position) minimum energy needed to react called Activation Energy

B. Collision Theory

C. 5 Factors Affecting Rates The speed that a reaction takes place can be affected by: Temperature Surface Area Stirring Concentration Catalysts We’ll discuss them one at a time.

1) Temperature Temp. Rate Why does milk last l0nger in the fridge? more energy, more collisions Direct or inversely proportional

2) Surface Area Surf. Area Rate more collisions

3) Stirring Stirring Rate more collisions

4) Concentration Conc. Rate more collisions

4) Concentration Conc. Rate

5) Catalysts speed up a reaction without being consumed. lower the activation energy. Like a party helps people meet each other and helps build friendships

Like a party helps people meet each other and helps build friendships

Why is H2O2 stored in dark plastic bottles? 5) Catalysts Demo: Genie in a Bottle catalyst written above arrow MnO2 2 H2O2  2 H2O + O2 DEMO: 40 mL 30% H2O2 in jar/bottle. tsp of MnO2 in tissue on string with cork stopper holding hanging. Why is H2O2 stored in dark plastic bottles?

Quick Quiz! 1) An increase in which one of the following will NOT increase the reaction rate? A) temperature B) concentration of reactants C) total mass of reactants D) surface area of reactants

Quick Quiz. 2) A catalyst speeds up a reaction by A) lowering the activation energy. B) increasing the temperature C) permanently changing in a reaction D) supplying energy to a reaction