which of the following was true for the system between time t1 and time t2? (a) the concentration of n2 decreased. (b) the temperature of the system decreased. (c) the number of effective collisions between h2 and n2 was zero. (d) the rates of the forward and reverse reactions were equal. (e) the rate of formation of nh3 molecules was equal to the rate of disappearance of h2 molecules.