self test 15.2A

[Mariane Sanchez 1E]

The average rate of the reaction N2(g) + 3 H2(g) --> 2 NH3(g) over a certain period is reported as 1.15 (mmol NH3) L -1 h -1. (a) What is the average rate over the same period in terms of the consumption of H2?

[Vasiliki G Dis1C]

To do this, you need to use the stoichiometric coefficients given in the equation to relate the rates to one another. You know that the rate NH3=rate H2 (2mol NH3/3mol H2), so the rate of NH3=(2/3)rate of H2. You take 1.15 and divide by 2/3, to get an answer of 1.72 mmolH2⋅L-1⋅h-1. To get the unique rate, you can use the coefficient in front of NH3. The unique average rate would be 1/2(1.15), which is 1/coeff.(average rate NH3), and you get the answer of 0.575 mmol⋅L-1⋅h-1. Hope this helps!