(a) A first order reaction is 50% complete in 30 minutes at 300K and in 10 minutes at 320k. Calculate activation energy (E_a) for the reaction. (b) Write the two conditions for collisions to be effective reaction. (c ) How order of reaction and molecurity differ towards a complex reaction?

(a) A first order reaction is 50% complete in 30 minutes at 300K and i

1.	(a) A first order reaction is 50% complete in 30 minutes at 300K and in 10 minutes at 320k. Calculate activation energy (E_a) for the reaction. (b) Write the two conditions for collisions to be effective reaction. (c ) How order of reaction and molecurity differ towards a complex reaction?
Answer» Solution :a) We need to calculate rate constants at 300K and 320 K Using the equations `t_(1//2)=0.693/k or k=0.693/t_(1//2)` `k_(300k)=0.693/(t_(1//2)(300K))=0.693/(30 minutes)=0.0231 minutes^-1` `k_(320 k)=0.693/(t_(1//2) 320 K)=0.693/(10 minutes)=0.0693 minutes^-1` Using ARRHENIUS equation, we have `log""(k_(320k))/(k_(300k))=E_a/(8.314JK^-1 mol^-1)=[(320-300)/(320 times 320)]` SUbstituting the values we have `(0.0693 minutes^-1)/(0.0231 minutes ^-1)=E_A/(8.314J K^-1 mol^-1) times (20K)/(96000 K.K)` `or 3=E_a/(8.314 JK^-1 mol^-1)times1/(4800K)` or `E_A=3 times 8.314 times 4800 J mol^-1` =`119.722 kJ mol^-1` (b) The colliding molecules must possess a certain minimum value of energy (threshold energy). The colliding molecules must have proper orientation to facilitate breaking of bonds and formation of new bonds. (c ) For COMPLEX reaction order is GIVEN by the slowest step and molecularity of the slowest step in same as the order of OVERALL reaction. Order is applicable to elementary as well as complex reactions whereas molecularity is applicable only for elementary reactions.