1. For all orders of reaction except the first order, half life is related to initial concentration as ____
a) t0.5 α CAon
b) t0.5 α CAo1-n
c) t0.5 α CAo2n
d) t0.5 α CAo
Explanation: The generalised equation is t0.5 = \(\frac{C_{A0}^{1-n}(2^{n-1}- 1)}{(n-1)k}.\) At half life time, for a reaction of order n, CA = 0.5CAo.
2. The relationship between t.0.5 and CAo for a zero order reaction is ____
a) t0.5 = \(\frac{1}{kC_{A0}} \)
b) t0.5 = \(\frac{1}{C_{A0}} \)
c) t0.5 = \(\frac{C_{A0}}{k}\)
d) t0.5 = \(\frac{C_{A0}}{2k}\)
Explanation: For zero order reaction, \(\frac{-dC_A}{dt}\) = k. t0.5 = \(\frac{C_{A0}- \frac{C_{A0}}{2}}{k}.\)
Hence, t0.5 = \(\frac{C_{A0}}{2k}.\)
3. For a zero order reaction, the slope of t0.5 and CAo is ____
a) 2
b) 3
c) 1
d) 0
Explanation: Slope is (1-n). At n=0, slope = 1.
4. What is the slope of the plot of ln (t0.5) and ln (CAo)? (Where n is the reaction order)
a) 1-n
b) 2-n
c) n
d) \(\frac{n}{2} \)
Explanation: The plot is a straight line of slope (1-n). The equation representing the relationship is ln (t0.5) = ln\((\frac{(2^{n-1}-1)}{(n-1)k})\) + (1 – n) ln (CAo).
5. If t0.5 = 100 minutes and initial concentration is 10, then the order of the reaction is ____
a) 4
b) -1
c) -2
d) 1
Explanation: t0.5 = \(C_{A0}^{1-n}.\)100 = 10(1 – n). Hence, n = -1.
6. The fractional conversion is expressed as____
a) \(\frac{C_A}{C_{A0}} \)
b) \(\frac{C_{A0}}{C_A} \)
c) \(\frac{1}{C_{A0}} \)
d) \(\frac{C_A}{kC_{A0}} \)
Explanation: Fractional conversion is the time required to reduce the concentration to any fraction. It is the ratio of final to initial concentration.
7. The time required to convert to a fraction of 0.7 for a first order reaction is ____
a) t0.7 = \(\frac{(0.7)}{C_{A0} k}\)
b) t0.7 = \(\frac{(-0.7)}{C_{A0} k}\)
c) t0.7 = \(\frac{(0.3)}{C_{A0} k}\)
d) t0.7 = \(\frac{(-0.3)}{C_{A0} k}\)
Explanation: The time for converting to any fraction, F is, tF = \(\frac{C_{A0}^{1-n}(F^{n-1}-1)}{(n-1)k}.\) At F = 0.7, t0.7 = \(\frac{C_{A0}^{1-2}(0.7^1- 1)}{k}.\)
8. Autocatalytic reactions are the ones in which ____
a) One of the products poisons the catalyst
b) There is no catalyst employed
c) Only one reactant is involved
d) One of the products catalyses the reaction
Explanation: In autocatalytic reactions, the reactant is catalyzed by a product. One of the products is also a reactant.
9. State true or false.
An autocatalytic reaction is represented as A + R → R + R where, A is a reactant and R formed as the product catalyses the reaction.
a) true
b) false
Explanation: Initially, the progress of the reaction requires more R. As the reaction proceeds, A is consumed. Hence, more of A is required for the reaction to occur as time proceeds.
10. State true or false.
Autocatalytic reactions are single order reactions.
a) true
b) false
Explanation: The rate expression for autocatalytic reactions is non linear. In the reaction A + R → R + R, the concentration of R has to be initially increased. The concentration of R should be decreased as reaction progresses to favour product formation.