Concept #1: Understanding Average or General Rate.
General or Average Rate is the change in the concentration of a compound over a period of time.
Example #1: The following equation shows the production of NO and H2O by oxidation of ammonia.
4 NH3 (g) + 5 O2 (g) → 4 NO (g) + 6 H2O (l)
a. What is the average rate of each compound in the balanced equation?
Example #2: b) What is the rate of NH3 in the reaction between 2 and 6 minutes at 40oC?
Example #3: c) Determine the instantaneous rate of the following reaction.
In a stoichiometry based question we are accustomed to doing a mole-to-mole comparison. Now in Chemical Kinetics, we will do instead a rate-to-rate comparison.
Example #4: The decomposition of dinitrogen pentoxide is described by the chemical equation:
2 N2O5 (g) ---> 4 NO2 (g) + O2 (g)
If the rate of disappearance or decomposition of O2 is equal to 2.20 M/min at a particular moment, what is the rate of appearance or formation of N2O5 at that moment?
Practice: The formation of alumina, Al2O3, can be illustrated by the reaction below: 4 Al (s) + 3 O2 (g) ----> 2 Al2O3 (s). At 750 K it takes 267 seconds for the initial concentration of Al2O3 to increase from 6.18 E-5 M to 5.11 E-4 M. What is the rate of Al?