CCL: how to calculate energy in kcal/mol for a particular temperature



Dear All,

Normally it is assumed that if the activation barrier is less than 20 kcal/mol, then the reaction occurs at ROOM TEMPERATURE.

how do we calculate it?
what is its formula?

how  can  we know corresponding energy in kcal/mol for some other temperature say 70 degree Celsius. 

thanking you.

kind regards and best wishes 
ashutosh
varanasi India