If for the reaction $$\ce{2HgCl2 (aq) + C2O4^2- (aq) -> 2Cl^- (aq) + 2CO2 (g) + Hg2Cl2 (s)}$$ The initial concentration of $\ce{HgCl2}$ is $0.0836~\mathrm{M}$ (first order), of $\ce{C2O4^2-}$ is $0.202~\mathrm{M}$ (second order), and the initial rate of formation of $\ce{Cl-}$ is $0.52\times10^{-4}~\mathrm{M\,s^{-1}}$, then to find $k$ I would do: $$\frac{1}{2}(0.52 \times 10^{-4}~\mathrm{M\,s^{-1}})=k(0.0836~\mathrm{M})(0.202~\mathrm{M})^2$$ And isolate for $k$. I included the one half in front of the rate of chloride ion formation because the coefficient in front of the chloride ion is 2 in the equation.

Is my method correct? The solution key states that I should set up my equation without the one half. Thus, its answer was twice as large as the one I got. If the answer key is correct, please explain why.

  • $\begingroup$ Maybe the initial rate already includes the factor of 1/2 $\endgroup$ – Aditya Dev Feb 29 '16 at 12:44
  • $\begingroup$ @AdityaDev That would be very confusing for a student doing this question on a test. As far as what I can tell, it only states the rate at which chloride ions are formed. That suggests to me it has not included the factor of 1/2. $\endgroup$ – lightweaver Feb 29 '16 at 13:12

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