# Homework Help: Reaction Mechanism Predictions

1. Aug 27, 2011

### kari82

A chemical Reaction A-->B is carried out in a closed vessel. The following data are taken for the concentration of A, Ca (g/L), as a function of time, t(min), from the start of the reaction. A proposed reaction mechanism predicts that Ca and t should be related by the expression

ln (Ca-Cae)/(Ca0-Cae)=-kt

where k is the reaction rate constant

Do the data (see attached file) supports this prediction? If so, determine the value of k. (Use a semilog plot in your solution for this problem)

Can someone explain to me what using a semilog plot means? And, maybe give me a hint on how to start this problem please.... Thank you!

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2. Aug 27, 2011

### MisterX

A [2-D] semilog plot has a logarithmic scale for only one axis.

To start the problem, I would exponentiate to get rid of the logarithm. Re-arange to solve for CA, and determine if the function's initial value and the value it approaches agree with the plot.

You should know what the plot of $f(t) = Ce^{-kt} + D$ would look like.

Know that if k is positive, the term $Ce^{-kt}$ will approach zero as t becomes larger.

You should be able to indentify (in terms of C and D):

• the value of this function when t = 0
• the value it approaches as t becomes larger

3. Sep 4, 2011

### kari82

Thank you so much for your help!!

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