Homework Problem 15.3

[Mike Matthews 1D]

Homework question 15.3: "In 20 s the concentration of nitrogen dioxide, NO2, decreases from 450 mmol.L-1 to 320 mmol.L-1 in the reaction 2NO2(g)--->2NO(g) + O2(g). Determine the rate of reaction of NO2" Why is it that in the answer key the rate of reaction of NO2 is not divided by its stoichiometric coefficient of 2?

[Julia Campbell 2F]

I think because the product also has a coefficient of two so it's a 1:1 ratio. Or maybe the concentrations given already factored that in.

[Lena Nguyen 2H]

The question asks for the rate of reaction of NO2 rather than the unique average rate of the reaction (which would divide the rate by 2). Therefore, the rate of reaction of NO2 is the change in NO2 over the change in time multiplied by -1.

[sofiakavanaugh]

I am also confused on this: if this is true then what exactly is the difference between rate of reaction and unique rate of reaction and why are they calculated differently?

[Kailey Brodeur 1J]

The rate of reactions cannot be generally inferred from the the chemical equation for the reaction. So the stoichiometric coefficients are the only thing to consider.