# Chemical Reaction Engineering Questions and Answers – Liquid and Gas Phase Reactions

This set of Chemical Reaction Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Liquid and Gas Phase Reactions”.

1. Which of the following is true for gas phase reactions?
a) Increase in moles of product increases the volume of the reaction mixture
b) Increase in moles of product decreases the volume of the reaction mixture
c) Decrease in moles of product increases the volume of the reaction mixture
d) Increase in moles of product does not affect the volume of the reaction mixture

Explanation: Increase in moles of product increases reaction mixture volume. For a reaction proceeding such that the moles of products are higher than moles of reactants, volume of reaction mixture increases.

2. For an ideal gas at any given temperature and pressure, the ideal gas law is used to express ____
a) Concentration of gas molecules
b) Mobility of gas molecules
c) Kinetic energy of gas molecules
d) Potential energy of gas molecules

Explanation: Ideal gas law is given as, PV = nRT,
Where, P – Pressure
T – Temperature
R – Universal gas constant
n – Number of gas moles
V – Volume
Concentration is the number of moles per unit volume = $$\frac{n}{V} = \frac{P}{RT}.$$

3. The progress of which among the following reactions results in an increase in volume?
a) A → B
b) 3A → B
c) A → 4B
d) 2A → B

Explanation: Increase in moles of product is depicted by the reaction, A → 4B. The number of moles of product is higher than that of reactant.

4. The rate of a gas phase reaction involving the conversion of reactant ‘i’ to product is expressed as ____
a) (-ri)=-$$\frac{1}{V^2}\frac{dN_i}{dt}$$
b) (-ri)=-$$\frac{1}{V}\frac{dN_i}{dt}$$
c) (-ri)=-$$\frac{dN_i}{dt}$$
d) (-ri)=-V$$\frac{dN_i}{dt}$$

Explanation: The rate of change of the gaseous component ‘i’ in due course of the reaction is the change in number of moles of ‘i’ per unit time per unit volume of the reaction mixture. Hence, (-ri)=-$$\frac{1}{V}\frac{dN_i}{dt}.$$

5. State true or false.
For a gas phase reaction, the rate of the reaction, (-rA)=-$$\frac{1}{V}\frac{dN_A}{dt}=-\frac{dC_A}{dt}$$ is valid only if A → B.
a) True
b) False

Explanation: The volume of reaction mixture remains constant as the number of moles of reactant and product is the same. Hence, the number of moles per unit volume does not vary during the progress of the reaction. Hence, the number of moles per unit volume is expressed as concentration of the reactant, A.
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