This quantity is the firs
This quantity is the first one examined when using the Hammond postulate.  The negative of this quantity divided by the gas constant is the slope of the line formed in a plot named for the same man who names the equation that calculates this quantity.  That expression is the negative product of the gas constant, temperature, and the natural log of the reaction rate over the pre-exponential factor, and is named for Arrhenius. Catalysts increase the reaction rate by lowering this quantity.  For 10 points, name this quantity, the minimum amount of energy needed for a reaction to occur.
This quantity is the first one examined when using the Hammond postulate.  
{activation} energy