Engineering Questions with Answers - Multiple Choice Questions

# Rocket Propulsion – Chemical Rocket Propellant – Background and Fundamentals

1 - Question

Consider a mixture of three gases a, b and c at equilibrium. If the individual gas components have pressures equal to Pa, Pb and Pc, determine the total pressure P of the mixture of gases.
a) P = Pa + Pb + Pc
b) P = Pa x Pb x Pc /(Pa + Pb + Pc)
c) P = [(Pa x Pb) + (Pb x Pc) + (Pc x Pa)] / (Pa + Pb + Pc)
d) P = (Pa x Pb / Pc) + (Pb x Pc / Pa) + (Pc x Pa / Pb)
Explanation: Dalton’s law of partial pressures states that the total pressure exerted by a mixture of gases is the sum of partial pressures of individual gas components. Hence the answer is P = Pa + Pb + Pc.

2 - Question

Perfect gas equation applies very closely to ________ gases.
a) low temperature, low pressure
b) high temperature, high pressure
c) high temperature, low pressure
d) low temperature, high pressure
Explanation: Perfect gas equations are valid for high temperature and low-pressure gases. In such a case, the inter-molecular forces are negligibly small. PV=RT is the perfect gas equation, with V as the specific volume, P as the pressure, T as the temperature and R as the gas constant for the mixture of gases.

3 - Question

Consider two sets of mixture of gases A and B having the same specific volume of the mixture and having total pressures PA and PB respectively. If TA = 3TB and molecular mass of A MA = 1/2 MB, determine the ratio of PA/PB.
a) 0.75
b) 12
c) 1.5
d) 6
Explanation: Assume that the gases follow the perfect gas equation. P = R’T/MVmix where Vmix is the specific volume of the mixture and R’ is the universal gas constant. So PA/PB = (TA/TB) x (MB/MA) = 3 x 2 = 6.

4 - Question

Consider two sets of mixture of gases X and Y having the same total temperature of the mixture and having total pressures PX and PY respectively. If PX = 1.4 PY and molecular mass of A MX = 2.3 x MY, determine the ratio of Vmix_X/Vmix_Y.
a) 0.26
b) 0.52
c) 0.62
d) 0.31
Explanation: Assuming the mixture of gases to be ideal, we have P = R’T/MVmix where Vmix is the specific volume of the mixture and R’ is the universal gas constant. PX/PY = (TX/TY) x (MYVmix_Y/MXVmix_X) Vmix_X/Vmix_Y = (MY/MX) x (TX/TY) x (PY/PX) = (1/2.3) x 1 x (1/1.4) = 0.31.

5 - Question

In a gaseous mixture, the number of moles and the molecular mass (in their respective units) of each component is given as follows: nA = 1, MA = 23; nB = 2, MB = 48; nC = 3, MC = 19. Find the average molecular mass of the mixture.
a) 28.67
b) 29.33
c) 31.25
d) 25.47
Explanation: Mavg = (nAMA + nBMB + nCMC) / (nA + nB + nC) = (23 + 96 + 57) / 6 = 29.33.

6 - Question

What is the number of condensed species in a gaseous mixture, if there are 8 possible species which enter into a relationship and out of these, only 5 are gases?
a) 3
b) 2
c) 9
d) 6
Explanation: If there are n species that enter into a relationship and if there are only m species out of these, then the total number of condensed species is n-m.

7 - Question

Determine the stoichiometric mixture mass ratio for the complete reaction: H2 + 1/2 O2 → H2O.
a) 2:1
b) 16:1
c) 4:1
d) 8:1
Explanation: On mass basis, stoichiometric mixture requires half of 32 kg of O2 with 2 kg of H2. So the mixture mass ratio would be 1/2 x 32 / 2 = 8.

8 - Question

Rocket propulsion usually operates in ___________ mixture ratio.
a) fuel rich
b) oxidizer rich
c) stoichiometric
d) any
Explanation: Rocket propulsion systems typically operate in fuel rich mixture ratio. This allows a portion of lightweight molecules such as hydrogen to be unreacted and contributes to the decrease in the average molecular mass of the combustion products.

9 - Question

The decomposition of solid propellants to reaction mixture is a(n) ______________ chemical reaction.
a) reversible
b) irreversible
c) stoichiometric
d) ideal
Explanation: The whole process of combustion of solid propellants to derive a reaction mixture is an irreversible chemical reaction. It means that the reverse process is not possible.

10 - Question

What is the energy released (or absorbed), or the enthalpy change when one mole of a chemical compound is formed from its constituent atoms or elements at one bar and isothermally at 25°C?
a) Heat of formation
b) Heat of reaction
c) Gibbs free energy
d) Latent heat of vaporization