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Reaction kinetics

Reaction kinetics

by vaibhav mathur -
Number of replies: 2

Please try to answer the following questions:

1. Rate of a reaction

a. Increases with increase in temperature

b. Decreases with increase in temperature

c. Does not depend on temperature

2. For a reaction mA + nB -> pC + qD, the rate law is given by dx/dt = k[A][B]. What is the molecularity of the reaction?

3. At equilibrium, if Kp=1, then

a. ∆G°= 1

b. ∆G°> 1

c. ∆G°< 1

d. None of these

4. Reaction A + 2B + C -> D occurs by the following mechanism

A + b -> X (fast, reversible)

X + C -> Y (slow)

Y + B -> D (very fast, reversible)

Then the order of reaction will be

a. 1

b. 2

c. 0

d. 3

5. Rate constant of a reaction is 1.2 mol/l.hr . Starting with 20mol/l, rate of reaction after 20 min will be

a. 2.8 mol/l.hr

b. 4.6 mol/l.hr

c. 9.6 mol/l.hr

d. 12.6 mol/l.hr

6. The slope of the line of the graph of log K and 1/T for the reaction N2O5 -> 2NO2 + 0.5O2 is -5000. The energy of activation for the reaction is

a. 23 kcal

b. 46 kcal

c. 54 kcal

d. 72 kcal

In reply to vaibhav mathur

Re: Reaction kinetics

by Srinath Murthy -

Rate increases generally with temp. and molecularity though is defined for elementary step can be taken as two for the second one. The standard free energy changes should be zero if eq. const. is 1.In 4 it should be third order. If you can post your own solutions it will be easier to help you.

In reply to Srinath Murthy

Re: Reaction kinetics

by vaibhav mathur -

Thanks for the reply. I will try to post some of my own solutions and doubts.

1. Does the rate of reaction always increase with temp? Are there reactions in which the rate does not depend on temp?

2. Shouldn’t the molecularity be m + n?

3. The answer is given as (a)

4. Considering rate constants k1, k2, k3, k4 and k5 resp. for each of the forward and backward reactions, rate of reaction= k3[X][C]. assuming d[X]/dt = 0, we get [X]= k1[A][B]/(k3[C] +k2).

So, rate of reaction= k3 k1[A][B][C]/(k3[C] +k2). What can we say about the order of the reaction from this expression?

5. From the units of the rate of reaction it is clear that the reaction Is a zero order reaction. Therefore the rate should be independent of concentration of reactant and equal to k. but no such option is present. The answer is given as (c).

6. Slope = -Ea/R. R=1.987≈2. so Ea=10 kcal. But there is no such option. The answer given is (a).