What is the minimum energy required for a chemical reaction to occur?

Determine and explain which of the following reactions is more rapid: reaction A with E_act = 10.5 kJ/mol (2.50 kcal/mol) or reaction B with  E_act = 20.9 kJ/mol (5.00 kcal/mol).

The activation energies of the forward and reverse reactions of a system are 50.0 kJ/mol (12.0 kcal/mol) and 75 kJ/mol (17.9 kcal/mol), respectively. Create an energy diagram for this system and determine whether the forward reaction is endergonic or exergonic.

Label the energy diagram shown below:

For the reaction

A + B → C + D

identify the arrow that represents the activation energy of the forward reaction.