1. Rate of a Reaction

2. Reaction Rate Reactant → products A B

3. rate = -  [A] tt rate = [B][B] tt  [A] = change in concentration of A over time period  t  [B] = change in concentration of B over time period  t *Because [A] decreases with time,  [A] is negative.

4. Average Rate averaged over a specific period of time Instantaneous Rate for a specific instance in time Rate = — [A] final – [A] initial t final - t initial Rate = Δ concentration Δ time Units: M or mol/L s s

5. Example Hydrogen reacts with chlorine to produce hydrochloric acid. Calculate the average reaction rate for all reactants

6. Example Br 2 (aq) + HCOOH (aq) 2Br - (aq) + 2H + (aq) + CO 2 (g) red-brown Determine the average rate for the consumption of molecular bromine for the following time intervals. a. first 50 sec b. first 100 sec time

7. slope of tangent slope of tangent slope of tangent

8. Avg. Reaction Rate and Stoichiometry 2A B Two moles of A disappear for each mole of B that is formed. rate =  [B] tt rate = -  [A] tt 1 2 aA + bB cC + dD rate = -  [A] tt 1 a = -  [B] tt 1 b =  [C] tt 1 c =  [D] tt 1 d

9. Review of Concepts Write a balanced chemical equation for a gas- phase reaction whose rate is given by

10. Collision Theory Summary: 1) reacting substances must collide 2) must collide with the correct orientation 3) must collide with sufficient energy

11. 11 Exothermic ReactionEndothermic Reaction The activation energy (E a ) is the minimum amount of energy required to initiate a chemical reaction. A + B AB C + D + +