# Chemical Engineering Questions and Answers – Material Balances Involving Ideal Gases

This set of Chemical Engineering Quiz focuses on “Material Balances Involving Ideal Gases”.

1. H2 at 27oC with pressure 10 atm and volume 10 liter is passed through a reactor with 6 moles of oxygen, if the limiting reagent reacts completely, how many moles of oxygen is left unreacted?
a) 1
b) 2
c) 4
d) 6

Explanation: The reaction is 2H2 + O2 -> 2H2O, moles of H2 passed = 10*10/(0.0821*300) = 4, => moles of H2 reacted = 4, => moles of O2 reacted = 4, => moles of O2 left unreacted = 6 – 2 = 4.

2. N2 with pressure 10 atm and H2 with pressure 30 atm, both with volume 10 liter at 27oC are passed into a reactor, how many moles NH3 is produced?
a) 4
b) 8
c) 12
d) 16

Explanation: The reaction is N2 + 3H2 -> 2NH3, moles of N2 = 10*10/(0.0821*300) = 4, moles of H2 = 30*10/(0.0821*300) = 12, => extent of reaction = (0 – 4)/(-1) = 4, => moles of NH3 = 4*2 = 8.

3. CH4 with pressure 10 atm and volume 5 liter at 27oC is passed into a reactor with 50% excess oxygen, how many moles of oxygen is left in the products?
a) 2
b) 4
c) 6
d) 8

Explanation: The reaction is CH4 + 2O2 -> CO2 + 2H2O, moles of CH4 = 10*5/(0.0821*300) = 2, => moles of O2 left = 2*2(50/100) = 2.

4. CO with pressure 10 atm at 27oC is passed through a reactor with O2, what is the pressure of CO2 produced if 60% CO reacted?
a) 2 atm
b) 6 atm
c) 10 atm
d) 14 atm

Explanation: The reaction is 2CO + O2 -> 2CO2, pressure of CO2 = 10*0.6 = 6 atm.

5. Glucose with pressure 10 atm at 27oC is passed through a reactor with O2, what is the temperature of CO2 produced if pressure becomes thrice?
a) 150 K
b) 240 K
c) 300 K
d) 330 K

Explanation: The reaction is C6H12O6+ 9O2 -> 6CO2 + 6H2O, => 30/T = 6(10/300), => T = 150 K.
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6. A gas mixture with 6% O2 with pressure 1 atm at 27oC is entered a reactor with rate F, and another stream with pure O2 with 2 atm pressure at 27oC entered the reactor with rate 1 liter/s, product has 10% O2 with same conditions with rate P, what is the value of F?
a) 575.5 liter/s
b) 725 liter/s
c) 895 liter/s
d) 997.5 liter/s

Explanation: Overall material balance: F + 1 = P, O2 balance: 0.06*F + 2*1*1 = 0.1*P, => 6F + 400 = 10P, => F = 399*2.5= 997.5 liter/s.

7. A mixture with 60% O2 and 40% H2 with pressure 5 Pa at 27oC at the rate 15 liter/s is passed through a reactor with another stream containing pure H2 with pressure 10 Pa at 27oC at the rate 5 liter/s, what is the fraction of H2 with pressure 5 Pa at 27oC in product?
a) 0.2
b) 0.4
c) 0.6
d) 0.8

Explanation: Overall material balance: 15 + 5 = P, => P = 20 mole/s, Overall O2 balance: 0.4*5*15 + 1*10*5 = 20*x*5, => x = 0.8.

8. A gas mixture has 10% CH4 with pressure 5 Pa at 27oC at the rate F, is passed through a reactor with another stream containing 60% CH4 with pressure 5 Pa at -73oC at the rate 10 liter/s, if the percentage of CH4 with pressure 5 Pa at 27oC in product is 80%, what is the value of F?
a) 1 liter/s
b) 1.4 liter/s
c) 2 liter/s
d) 2.6 liter/s

Explanation: Overall material balance: F + 10 = P, Overall CH4 Balance: 0.1*F*5/300 + 0.6*10*5/200 = 0.8*P*5/300, => F + 90 = 8P, => F = 10/7 = 1.4 liter/s.

9. A gas mixture with 50% H2 at the rate F is passed through a reactor and it produced a gas mixture with 80% H2 at the rate 15 liter/s, what is the value of F?
a) 5 liter/s
b) 8 liter/s
c) 15 liter/s
d) 24 liter/s

Explanation: Overall H2 balance: 0.5F = 0.8*15, => F = 24 liter/s.

10. A gas mixture with 20% O2 with pressure 100 Pa at 27oC at the rate 50 liter/s is passed through a reactor and products a gas mixture with 40% O2 with pressure 25 Pa at 27oC, what is the rate of product?
a) 50 liter/s
b) 100 liter/s
c) 200 liter/s
d) 400 liter/s

Explanation: O2 balance: 0.2*100*50 = 0.4*25*P, => P = 100 liter/s.

11. A gas mixture with 10% H2 with pressure 15 Pa at 27oC at the rate 20 liter/s is passed through a reactor and products a gas mixture with 30% H2 with pressure 25 Pa at 27oC, what is the rate of product?
a) 4 liter/s
b) 10 liter/s
c) 24 liter/s
d) 30 liter/s

Explanation: H2 balance: 0.1*15*20 = 0.3*25*P, => P = 4 liter/s.

12. A gas mixture with 50% Ar with pressure 80 Pa at 0oC at the rate 5 liter/s is passed through a reactor and products a gas mixture with 80% Ar with pressure 50 Pa at 27oC, what is the rate of product?
a) 5 liter/s
b) 10 liter/s
c) 20 liter/s
d) 40 liter/s

Explanation: Ar balance: 0.5*80*5 = 0.8*50*P, => P = 5 liter/s.

13. A gas mixture with 5% Neon with pressure 10 atm at 27oC is entered a reactor with rate F, and another stream with pure Neon with 8 atm pressure at 27oC entered the reactor with rate 3 liter/s, product has 10% Neon with same conditions with rate P, what is the value of F?
a) 3 liter/s
b) 15 liter/s
c) 48 liter/s
d) 72 liter/s

Explanation: Neon balance- 0.05*F*10 + 3*1*8 = 0.1*P*8, => 0.5F + 24 = 0.8P, Overall balance- F + 3 = P, => 0.3F = 21.6, => F = 72 liter/s.

14. CH4 with pressure 10 atm and volume 10 liter at 27oC is passed into a reactor with 20% excess oxygen, how many moles of oxygen is left in the products?
a) 2
b) 4
c) 6
d) 8

Explanation: The reaction is CH4 + 2O2 -> CO2 + 2H2O, moles of CH4 = 10*10/(0.0821*300) = 4, => moles of O2 left = 2*4(50/100) = 4.

15. A gas mixture with 20% Neon with pressure 3 atm at 27oC is entered a reactor with rate F, and another stream with pure Neon with 2 atm pressure at 27oC entered the reactor with rate 5 liter/s, product has 40% Neon with same conditions with rate P, what is the value of F?
a) 3 liter/s
b) 15 liter/s
c) 30 liter/s
d) 45 liter/s

Explanation: Neon balance- 0.2*F*3 + 5*2*1 = 0.4*P*2, => 0.6F + 10 = 0.8P, Overall balance- F + 5 = P, => F = 30 liter/s.

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