Cliffs AP Chemistry, 3rd Edition

7. The activation energy is represented by

A. A

B. B

C. C

D. B –A

E. B –C

Answer: D

The activation energy is the amount of energy that the reactants must absorb from the system in
order to react. In the reaction diagram, the reactants begin at A. The reactants must absorb the
energy from Ato Bin order to form the activated complex. The energy necessary to achieve
this activated complex is the distance from Ato Bin the diagram and is mathematically the dif-
ference (B –A).

8. The enthalpy of the reaction is represented by

A. B – (C – A)

B. B

C. C – A

D. B – C

E. A – (B – C)

Answer: C

The enthalpy of the reaction, ∆H, is the difference between the enthalpies of the products and
the enthalpies of the reactants.

∆H= Hproducts−Hreactants

The products are represented at point Cand the reactants are represented at point A, so the
change in enthalpy is C −A.

Kinetics