# Chemical Reaction Engineering Questions and Answers – Stoichiometry – Constant – Volume Batch Reaction Systems

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This set of Chemical Reaction Engineering Assessment Questions and Answers focuses on “Stoichiometry – Constant – Volume Batch Reaction Systems”.

1. State true or false.
Constant volume system means that the volume of reactor is constant.
a) True
b) False

Explanation: The volume of the reaction mixture remains constant for a constant volume system. The system is incompressible.

2. Which of the following represents constant volume system?
a) C + O2 → CO2
b) CO + H2O → CO2 + H2
c) N2 + 3H2 → 2NH3
d) SO2 + 0.5O2 → SO3

Explanation: Gas phase reactions in which the number of moles of the product is equal to the number of moles of reactant is a constant volume system. In CO + H2O → CO2 + H2, 2 moles of reactants form 2 moles of product.

3. What is the partial pressure of the product related to the total pressure for a constant volume system? (Where pR is the partial pressure of the product, pR0 is the initial partial pressure of the product, P is the total pressure, P0 is the initial pressure of reaction mixture, r is the stoichiometry of the product and ∆n is the difference between the number of moles of the product and the number of moles of the reactant)
a) pR = $$\frac{r}{∆n}$$ (P – P0)
b) pR = pR0 – $$\frac{r}{∆n}$$ (P – P0)
c) pR = pR0 + (P – P0)
d) pR = pR0 + $$\frac{r}{∆n}$$ (P – P0)

Explanation: For the reaction, aA + bB → rR + sS, pR = CRRT. CR is the product concentration. CRRT = pR0 + $$\frac{r}{∆n}$$ (P – P0).

4. The desired relationship between the partial pressure of reactant and total pressure for the reaction N2O4 → 2NO2 is _____
a) PA = PA0 – 2(P – P0)
b) PA = 2PA0 – (P – P0)
c) PA = PA0 – (P – P0)
d) PA = PA0 + (P – P0)

Explanation: ∆n = 2-1 =1. pA = pA0 – $$\frac{a}{∆n}$$ (P – P0), a is the stoichiometry of the reactant. Hence, PA = PA0 – (P – P0).

5. If the total pressure for reaction is initially is 2 atm and the pressure is changed to 3 atm for the reaction to occur, then the value of (PA – PA0) for the reaction N2O → N2 + 0.5O2 is ____
a) -2
b) 2
c) -1
d) 1

Explanation: ∆n = 0.5
pA = pA0 – $$\frac{a}{∆n}$$ (P – P0)
(PA = PA0) = $$\frac{-1}{0.5}$$(3-2)
(PA = PA0) = -2.