# Environmental Engineering Questions and Answers – Kinetics of Chemical Disinfection

This set of Environmental Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Kinetics of Chemical Disinfection”.

1. Consider the following variables.
i. Concentration of disinfectant
ii. Concentration of organisms
iii. Temperature
iv. Time of contact
Disinfection is the function of which of the following variables?
a) i, ii
b) i, ii, iii
c) i, ii, iii, iv
d) ii, iii, iv

Explanation: The process of disinfection is the function of concentration of disinfectant, organisms, temperature of disinfection and time of contact.

2. According to which of the following, organism destroyed by disinfection is proportional to organism remaining?
a) Hazens equation
b) Chicks law
c) Darcy’s law
d) Rose equation

Explanation: According to Chicks law of disinfection, the number of organisms destroyed in unit time is proportional to the number of organisms remaining.

3. Which of the following is the expression of Chicks law?
a) Dy/Dt = k (N – y)
b) Dy/Dt = k/(N – y)
c) Dy/Dt = k (N + y)
d) Dy/Dt = k (N * y)

Explanation: The expression of Chicks law is given by Dy/Dt = k (N – y) Where, N is the number of organisms initially present, ‘y’ is the number of organisms remaining after time t and k is the coefficient of proportionality.

4. The integration of the expression of Chicks law is given by ____________
a) N1/N = ekt
b) N1/N = kt
c) N1/N = k/t
d) N1/N = e-kt

Explanation: According to Chicks law, Dy/Dt = k (N – y), by integration,
loge N1/N = -kt
= N1/N = e-kt Where, N1 = N – y.

5. The dimensional formula of rate constant used in Chicks law is ____________
a) 1/t
b) 1/t2
c) 1/t3
d) t2

Explanation: According to Chicks law, Dy/Dt = k (N – y) where, k is the rate of proportionality or rate constant having dimensional formula 1/t.
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6. The number of organisms destroyed is equal to the number of organisms remaining at time t = __________
a) 0
b) 1
c) 2
d) 10

Explanation: According to Chicks law, N1/N = e-kt, when t=0,
N1/N = 1 or N1 = N, Where, N1 represents the remaining organisms.

7. The expression loge N1/N = – kt m Where m is a constant such that m>1 represents ____________
a) Rate of the kill will remains constant with time
b) Rate of the kill will increase with time
c) Rate of the kill will decrease with time
d) Rate of the kill is directly proportional to time

Explanation: The expression loge N1/N = -ktm Where m is a constant such that m>1 represents that rate of kill will increase with time whereas m<1 represents rate of the kill decrease with time.

8. For changing the concentration of disinfectant, the disinfecting efficiency is expressed by ____________
a) C n *t p = Constant
b) C n/ t p = Constant
c) C q * Np = Constant
d) C q / Np = Constant

Explanation: The disinfecting efficiency is expressed by C n *t p = Constant where, C is the concentration of disinfectant, t p is the time required to kill the organism and n is the coefficient of dilution.

9. The number of organisms in disinfection process can be expressed by ____________
a) Cn *t p = Constant
b) C n / tp = Constant
c) C q * Np = Constant
d) C q / Np = Constant

Explanation: The number of organisms in disinfection process can be expressed by Cq * Np = Constant where, C is the concentration of disinfectant, the Np is the reduced concentration of organisms and q is the coefficient of disinfectant strength.

10. Efficiency of dilution decreases rapidly when the coefficient of dilution is ____________
a) 0
b) 1
c) <1
d) >1

Explanation: Efficiency of dilution decreases rapidly when the coefficient of dilution n is greater than 1 which is a measure of order of reaction.

11. When the coefficient of dilution is 1, then which of the following statement is correct?
a) Time of contact is more important than dosage
b) The dosage is more important than time of contact
c) Concentration and time are equally important
d) Efficiency of dilution decreases.

Explanation: When the coefficient of dilution is 1, concentration and time are equally important and a first order will proceed.

12. The temperature of disinfection is inversely proportional to the killing of organisms.
a) True
b) False

Explanation: The temperature of disinfection is directly proportional to the killing of organisms and the increase in temperature results in more rapid killing of organisms.

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