Determining Activation Energy

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The activation energy can be determined by finding the rate constant of a reaction at several different temperatures.

Temperature, °C k, M-1•s-1
24 1.3 x 10-3
28 2.0 x 10-3
32 3.0 x 10-3
36 4.4 x 10-3
40 6.4 x 10-3

Notice that when the Arrhenius equation is rearranged as above it is a linear equation with the form y = mx + b; y is ln(k), x is 1/T, and m is -Ea/R. The activation energy for the reaction can be determined by finding the slope of the line.

 -Ea/R = slope

Ea = -R•slope

Which R? well what is the unit for Ea?

Ea is in J/mol so are you going to use the constant 0.08206 L•atm•mol-1•K-1 or are you going to use the constant 8.314 J•mol-1•K-1.

Ea = -8.314 J•mol-1•K-1(-9253 K)

Ea = 76929 ==> 77,000 J/mol

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