276) A first order reaction takes 69.3 minutes for 50% completion. How much time will be needed for 80% completion?

277) For the non equilibrium process, A + B → products, the rate is first order with respect to A and second order with respect to B. If 1.0 mol of each of A and B are introduced into a 1 litre vessel, and the initial rate were 1.0 x 10⁻² mol⁄litre sec, calculate the rate when half of the reactants have been used:

278) The half time period t_(1⁄2) is independent of the initial concentration of reactant when the order of reaction is:

279) The rate constant of a zero order reaction is 0.2 mol dm⁻³hr⁻¹ of the concentration of the reactant after 30 minutes is 0.05 mol dm⁻³ then its initial concentration would be:

280) Collision theory is applicable to :