An experiment was designed to the study the reaction kinetics of a reaction that contains the reactants A, B, and C. Given the following data:

Question

An experiment was designed to the study the reaction kinetics of a reaction that contains the reactants A, B, and C. Given the following data:

This is supposed to be a table:

A₀ (mol L⁻¹) B₀ (mol L⁻¹). C₀ (mol L⁻¹). Initial Rate (mol L⁻¹ s⁻¹)

0.100. 0.100 0.250 1.25

0.200 0.100 0.250 2.50

0.100 0.200 0.250 1.25

0.200 0.100 0.500 10.00

What would the rate of the reaction be (in mol L⁻¹ s⁻¹) when concentration of A = 0.573 mol L⁻¹, B = 0.297 mol L⁻¹, and C = 0.195 mol L⁻¹?

Answer 1

Comparing lines 1 & 2:

[A] doubles, [B] and [C] remain constant; rate doubles; ---> 1st order in A

Compare lines 1 & 3:

[B] doubles, [A] and [C] remain constant; rate stays the same ---> zero order in B

Compare lines 2 & 4:

[C] doubles, [A] and [B] remain constant; rate increases 4x ---> 2nd order in C

Rate Law: rate = k[A][C]²

We can use any line to solve for k; using line 1 we have....

1.25 M/s = k[0.1 M][0.25 M)² = 0.00625 M³ k

k = 200 M^-2s^-1

Now that we have the rate constant, k, we can find the rate given the concentrations of the reactants:

rate = k[A][C]² = 200 M^-2s^-1 (0.573 M)(0.195 M)²

rate = 4.36 Ms^-1 = 4.36 M L^-1 s^-1

Answer 2

Lines 1, 2, and 4 of the data indicate that the rate equation is R₀ = k x A₀ x C₀²) /B₀ in which case you can substitute the given data and calculate the rate constant k which turns out to be 20. Line 3, however, doesn't seem to fit the rest of the data. Are you sure line 3 data is correct?

Answer 3

Hi Sara B.,

Inspect your rate data table to find the reaction order for [A0], [B0], and [C0]. You will see clearly evident ratios are present in those reactants across the 4 trials. For example, if a reactant doubles, and the rate doubles, the reaction order in that reactant is 1 (the concentration is raised to the 1 power in the reaction rate total calculation). You should be able to figure out that orders of 0, 1, and 2 obtain for the three reactants -- but not necessarily in that alphabetical order! Figure the ratios for the "new" conditions for each reactant vs. those in one of the 4 trials, and using those orders as exponents. And solve the resulting expression; that is what you must multiply the rate in that one trial to get the answer.

-- Cheers, --Mr. d.