## Full Length 2 CP Q19

NS_Tutor_Sophia
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Joined: Tue Aug 01, 2017 11:49 am

### Full Length 2 CP Q19

A student recently asked us how to determine the reaction rate for the following question: "Which of the following is the rate constant for Reaction 2?"

To answer this question, we have to turn to Table 1 presented in the passage, which presents the reaction rate at different concentrations of O2 and NO. The key to determing the rate law based on experimental data is to determine how the reaction rate and one reactant change between two trials while all other reactant concentrations stay constant, and then repeat this for each reactant.

Based on Table 1, we want to first compare trials 1 and 2 so we can compare the effect of [O2] on reaction rate while NO stays constant. Between these trials, the reaction rate triples as the O2 concentration triples. Since there is a linear, one-to-one relationship between the two, [O2] will be raised to the power of 1 in the rate law.

Now we want to compare trials 1 and 3 so we can evalute the effect of [NO] on reaction rate while O2 stays constant. Between these trials, the reaction rate increases 9X as the NO concentration increases 3X. Since there is an exponential relationship between the two (3^2 = 9), [NO] will be raised to the power of 2 in the rate law.

Thus, the rate law is: rate = k[O2][NO]^2
Sophia Stone
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