15.65 Part b

Arrhenius Equation: $\ln k = - \frac{E_{a}}{RT} + \ln A$

Rachel N 1I
Posts: 48
Joined: Thu Jul 27, 2017 3:00 am

15.65 Part b

15.65 For the reversible, one-step reaction 2 A ---> B + C,
the forward rate constant for the formation of B is 265 L/(mol*min) and the rate constant for the reverse reaction is 392 L/(mol*min). The activation energy for the forward reaction is 39.7 kJ mol 1 and that of the reverse reaction is 25.4 kJ/mol .
(b) Is the reaction exothermic or endothermic?

Can someone explain how they determined whether it was endo or exo? Thanks!

Gwyneth Huynh 1J
Posts: 30
Joined: Fri Sep 29, 2017 7:05 am

Re: 15.65 Part b

The reaction is endothermic because the forward reaction has a higher activation energy than the reverse reaction. That means that the forward reaction requires more energy than the reverse. If you draw it out, the reactants are lower in energy than the products.

Ishan Saha 1L
Posts: 60
Joined: Fri Sep 29, 2017 7:03 am

Re: 15.65 Part b

You can determine whether or not the reaction is endothermic or exothermic by looking at the Activation energies. Because the activation of the forward reaction is greater than that of the reverse reaction, it can be determined that the reaction is endothermic. If you think of this graphically, the reaction starts at some point A, then goes up a large amount which is the forward reaction's Ea(let's call this point B), and then comes back down to the final energy level point C. We can tell that because the activation energy of the reverse reaction is less than that of the forward reaction, the difference between point C and point B (which is the Ea of the reverse reaction) will be less than the difference between point A and point C (which is the Ea of the forward reaction). This means that the reaction ends up at a higher energy state than what it started at, and overall energy will be absorbed.