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Wize University Chemistry Textbook > Kinetics

Measuring Ea Given a Graph

Arrhenius EquationPrevious Section
Collision Theory and Activated Complex TheoryNext Section
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How Do We Measure Ea

  • If we take the Arrhenius equation and rearrange it into linear form we can use graphical methods to find an experimental activation energy, Ea.
k=Ae−EaRTln⁡(k)=−EaR1T+ln⁡(A)\begin{array}{c} k=Ae^{-\frac{E_a}{RT}} \\ \\ \ln(k)=-\frac{E_a}{R}\frac{1}{T}+\ln(A) \end{array}
  • If we plot ln(k) vs 1/T we can determine the activation eneregy of the reaction from the slope of the straight line.
m=−EaRm=-\frac{E_a}{R}

Use the graph below to calculate the activation energy of the reaction below.

CH2CH2(g)+Cl2(g)→CH2ClCH2Cl(g)\textrm{CH}_2\textrm{CH}_{2(g)} + \textrm{Cl}_{2(g)}\rightarrow \textrm{CH}_2\textrm{Cl}\textrm{CH}_2\textrm{Cl}_{(g)}


Extra Practice
Given the following potential energy diagram for the one-step reaction, the activation energy of the reverse reaction is equal to ________.
X+Y→Z+RX+Y→Z+R
Given the following potential energy diagram for the one-step reaction, the activation energy of the reverse reaction is equal to ________.
X+Y→Z+RX+Y→Z+R
In Houston (near sea level) water boils at 100.0 °C. In Colorado (9500 ft. above sea level) water boils at 90.0°C. If it takes 4.8 min to cook an egg in Colorado and 4.5 min in Houston, what is Ea for this process?
For the reaction:
ABC+D↔AB+CDABC + D \leftrightarrow AB+CD
ΔH = -55 kJ/mol and the Ea for the forwards direction is 215 kJ/mol Sketch a reaction energy diagram for this process and calculate the activation energy for the reverse process, assuming a one-step reaction.