Q20 of 27 Page 1

The following data were obtained during the first order thermal decomposition of N2O5(g) at a constant volume:

2 N2O5(g)2 N2O4 + O2(G)



Calculate the rate constant.


OR


Two reactions of the same order have equal pre exponential factors but their activation energies differ by 24. 9 kJ mol - 1. Calculate the ratio between the rate constants of these reactions at 27°C. (Gas constant R = 8. 314 JK - 1mol - 1. )

2 N2O5(g)2 N2O4 + O2(G)


GIVEN,


At t = 0 0. 5 atm 0 atm 0 atm


At time t 0. 5 - 2x atm 2x atm x atm


To find total pressure:


Pt = sum of partial pressures of all reactants and products


Pt = 0. 5 - 2x + 2x + x


x = pt - 0. 5


p = 0. 5 - 2x


= 0. 5 - 2(pt - 0. 5)


= 1. 5 - 2pt


At t = 100 s ;pt = 0. 512 atm


p = 1. 5 - 20. 512 = 0. 476 atm


Formula to find rate constant of a first order reaction


k = log


k = log


k = 0. 0216 = 4. 9810 - 4 s – 1


conclusion


the rate constant for the following reaction is 4. 9810 - 4 s - 1


OR


Given:


Difference between activation energies = 24. 9 kJ/mol


The Arrhenius equation:


take log on both sides, log k = log (Ae-Ea)


log k = log A -


LETS ASSUME,


For reaction 1 log k1 = log A -


For reaction 2 log k2 = log A -


Subtract 1 from 2






Conclusion:


Ratio between rate constants = 2. 198 4


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