The *trans* → *cis* isomerisation of 1,2-dichloroethylene proceeds with an activation energy of 55.5 kcal mol-1. The heat of reaction at constant pressure for above transformation is 1.0 k cal mol-1. The activation energy for *cis* → *trans* transformation of 1,2-dichloroethylene is :
a. 56.5
b. 54.5
c. 55.5
d. none of these