Reaction Rates and Stoichiometry

1. -[C4H9Cl] t Rate = = [C4H9OH] t Reaction Rates and Stoichiometry C4H9Cl(aq) + H2O(l) C4H9OH(aq) + HCl(aq) • In this reaction, the ratio of C4H9Cl to C4H9OH is 1:1. • Thus, the rate of disappearance of C4H9Cl is the same as the rate of appearance ofC4H9OH.

2. 1 2 [HI] t Rate = − = [I2] t Reaction Rates and Stoichiometry What if the ratio is not 1:1? 2 HI(g)  H2(g) + I2(g)

3. aA + bB cC + dD = − = = Rate = − 1 b 1 a 1 c 1 d [D] t [C] t [A] t [B] t Reaction Rates and Stoichiometry • To generalize, then, for the reaction Sample Exercise 14.3 p. 563

4. Concentration and Rate One can gain information about the rate of a reaction by seeing how the rate changes with changes in concentration.

5. Sulfur Clock Demonstration Data

6. N2(g) + 2 H2O(l) NH4+(aq) + NO2−(aq) Concentration and Rate If we compare Experiments 1 and 2, we see that when [NH4+] doubles, the initial rate doubles.

7. N2(g) + 2 H2O(l) NH4+(aq) + NO2−(aq) Concentration and Rate Likewise, when we compare Experiments 5 and 6, we see that when [NO2−] doubles, the initial rate doubles.

8. aA + bB products What is Rate Law?

9. Concentration and Rate • This means the Rate  [NH4+] & Rate  [NO2−] Rate  [NH4+] [NO2−] which, when written as an equation, becomes Rate Law Eqn= k [NH4+]m[NO2−]n • This equation is called the rate law, andkis the rate constant. mandnare calledreaction orders. Therefore,

10. What are m and n exponents? • Exponents indicate how the rate is affected by each reactant concentration – termed reaction orders. • Rate Law must be determined experimentally.

11. Overall Reaction Order Rate = k [NH4+]m[NO2−]n • The overall reaction order can be found by adding the exponents on the reactants in the rate law … so m + n = ? 1 + 1 = 2 • This reaction is second-order overall.

12. Rate Constant (k) • Reveals how fast or slow rxn proceeds. • LARGE k (~ 109 ) = FAST • small k ( < or = 10 ) = SLOW

13. Sample Exercise 14.6 • Homework Chemical Kinetics: Rate Laws WS