12. The decomposition of NOCl has k= 9.3 x 10s M-s-1 at 100. °C and an Activatio
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12. The decomposition of NOCl has k= 9.3 x 10s M-s-1 at 100. °C and an Activation Energy of 98.9 Kj/mole, what is the rate constant at 130 "C 13 Consider the reaction Cg) Cl2(g)COCI2(g) The reaction is first order in CO and 3/2 order in Clz a) b) Write down the rate law for this reaction. what will be the rate of the reaction when [CO] = 0.025 M and [C12] = 0.015 M, given that the rate constant is 11 M-3/2s-1 14. The decomposition of NOBr follows second order kinetics. The rate constant is found to be 0.556 Ms1 If the initial concentration of NOBr in the container is 0.25 M, how long will it take for the concentration to decrease to 0.025 M? What is the half-life of the decomposition when the initial reactant concentration is 0.25 M? 15. Using the diagram above: (A) add the axes (B) label the activation energies (C) How many elementary steps are there? (D) Which elementary step is limiting? (E) What might happen if a catalyst is added. Show this effect on the diagram. 16 A possible mechanism for the overall reaction Br2(eNO (g) 2 NOBr (g) is Step 1: NO (g) Br2 (g) NO Br2 (g) k.1 (fast) k2 Step 2: NO Br e NO (g)2NOBr (slow) The reaction is experimentally determined to be second order in NO and first order in Br2 a) b) Write down the experimentally determined rate law Is the mechanism consistent with the observed rate law? 17. Suppose a reaction occurs with the following mechanism. 2 A A Step 1 Step 2 fast, equilibrium slow (A) (B) (C) (D) (E) What is the overall reaction? What are the intermediates in the mechanism? What is the molecularity of each step? Which is the rate determining step? What is the rate law predicted by this mechanism?Explanation / Answer
12) Arrhenius equation
ln(K2/k1) = Ea/R[1/T1 - 1/T2]
k1 = 9.3*10^5 , T1 = 373 k
k2 = ? , T2 = 403 k
Ea = 98.9 kj/mol , R = 8.314*10^-3 j.k-1.mol-1
ln(x/(9.3*10^5)) = ((98.9)/(8.314*10^-3))((1/373)-(1/403))
x = K2 = 9.99*10^6 M-1.S-1
13)
a) rate law, rate = k[CO][Cl2]^3/2
b) rate = 11*0.025*0.015^(1/2)
= 0.034 M.s-1
14) second order kinetics.
K2 = x/t*(a)*a0
k2 = 0.556 M-1.S-1
x = reacted = 0.225 M
a0 = initial no of concentration ofreactant = 0.25 M
a = concentration after time,t sec = 0.025 M
t = time = ?sec
0.556 = 0.225/(t*(0.025)*0.25)
t = 64.75 sec
ii)
0.556 = 0.125/(t*(0.125)*0.25)
t1/2 = half life time = 7.2 sec
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