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Standard XII

Chemistry

Activation Energy

The recombina...

Question

The recombination of methyl radicals has no activation barrier. The activation energy values for the first step in the thermal thermal decomposition of acetaldehyde given and $E_{p h o t o c h e m i c a l}$ are $309.32 k J m o l^{- 1}$ and $41.8 k J m o l^{- 1}$ respectively.
Calculate the overall activation energy for the thermal decomposition of acetaldehyde.

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Solution

$E_{t h e r m a l} = E_{2} + \frac{1}{2} E_{1} - \frac{1}{2} E_{4} = 1 / 2 E_{1} + E_{p h o t o} (a s, E_{p h o t o} = E_{2} - 1 / 2 E_{4}) E_{t h e r m a l} = 1 / 2 \times 309.32 + 41.8 = 196.46 k J / m o l$

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Ethermal=E2+12E1−12E4=1/2E1+Ephoto(as,Ephoto=E2−1/2E4)Ethermal=1/2×309.32+41.8=196.46kJ/mol

$E_{t h e r m a l} = E_{2} + \frac{1}{2} E_{1} - \frac{1}{2} E_{4} = 1 / 2 E_{1} + E_{p h o t o} (a s, E_{p h o t o} = E_{2} - 1 / 2 E_{4}) E_{t h e r m a l} = 1 / 2 \times 309.32 + 41.8 = 196.46 k J / m o l$