At a temperature of 700 K, the forward and reverse rate constants for the reaction 2 HI1g2 ΔH21g2 + I21g2 are kf = 1.8 * 10-3 M-1 s-1 and kr = 0.063 M-1 s-1. (b) Is the forward reaction endothermic or exothermic if the rate constants for the same reaction have values of kf = 0.097 M-1 s-1 and kr = 2.6 M-1 s-1 at 800 K?