Practice Problem 8

Hydrogen iodide decomposes to give a mixture of hydrogen and iodine:

2 HI(g) <----> H2(g) + I2(g)

Use the following data to determine whether the decomposition of HI in the gas phase is first order or second order in hydrogen iodide.

               Initial (HI) (M)          Initial Instantaneous

                                                 Rate of Reaction (M/s)         

Trial 1:     1.0 x 10-2                   4.0 x 10-6

Trial 2:     2.0 x 10-2                   1.6 x 10-5

Trial 3:     3.0 x 10-2                   3.6 x 10-5


Answer

The reaction is second order in HI:

Rate = k(HI)2

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