3. Two mechanisms have been proposed for the reaction: The first mechanism was a
ID: 865155 • Letter: 3
Question
3. Two mechanisms have been proposed for the reaction: The first mechanism was a single step mechanism: In 1967 a second, now more accepted mechanism was proposed: a- Determine the rate law for the first mechanism b- Determine the rate law for the second mechanism. Use the Steady State Approximation. In other words assume that the concentration of the intermediate is in a steady state. c- Determine the rate law for the second mechanism. Use the rapid equilibrium approximation for the first step. d- Under what conditions do the results for mechanism 2 agree? d- k3 has been determined independently at two temperatures, as Is shown below. Calculate the Activation Energy.Explanation / Answer
d) The concentrations of the reactants must be kept constant for studying the mechanism under steady state approximation.The reaction to be carried in a closed container.
activation energy can be determined by Arrhenius Equation , K = Ae -Ea/RT ,
Ea = activation energy, A = a constant , frequency factor
R = gas const.
so , log K = log A - -Ea/2.303RT
WRITE THE EQUATION FOR TWO DIFFERENT TEMPERATURES, PLEASE NOTE,K1 AND K2 ARE HERE K3 AT TWO DIFFERENT TEMPERATURES
log K1 = log A - -Ea/2.303RT1
log K2 = log A - -Ea/2.303RT2, [T1, T2 are two temperatures at two rate constants can be understood]
rearranging the above two equations we get ,
Ea = R*2.303*log(K2/K1)/(T2-T1/T1T2) [GAS CONSTANTR = 2 CAL/ DEGREE.MOLE]
substitute values,
= 2*2.303*log(K2/K1)/(T2-T1/T1T2)
= 4.606* log (4*106 /1.12*106 )/102.2/417.9*520.1
= 4.606 * 0.5828/102.2/ 217349.8
= 4.606 * 0.5828/217349.8/ 102.2
= 5708.9 calories/mole
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