250+ TOP MCQs on Classes of Reactions and Physicochemical Mechanism and Answers

By engineer / May 26, 2024

Answer: b
Clarification: 2TiH₂ + N₂ → 2TiN + 2H₂ represents reaction of the elements with decomposition products type of SHS reaction; Ni + Al → NiAl represents synthesis from element; B₂O₃ + TiO₂ + 5Mg → TiB₂ + 5MgO represents redox reaction; and 2BH₃N₂H₄ → 2BN + N₂ + 7H₂ represents thermal decomposition type of SHS reaction.

8. In SHS reactions, an important parameter is the _________
a) Isothermal temperature
b) Volumetric expansion
c) Adiabatic temperature
d) Heat
Answer: c
Clarification: In SHS reactions, an important parameter is the adiabatic temperature, T_ad. This refers to the temperature to which the products are raised under adiabatic conditions due to the heat evolved during the chemical reaction. If this temperature is less than the boiling point of both the constituents, no vapor phase is formed.

9. In the case of TiB₂, high pressures are needed to make it a gasless combustion.
a) True
b) False
Answer: a
Clarification: In case of TiB₂, though the adiabatic temperature is less than the boiling point of Ti and B, the vapor pressure of the elements at the adiabatic temperature is high, and hence high pressures are needed to make it a gasless combustion.

10. Solid state combustion leads to _______ combustion velocities.
a) Highest
b) Lowest
c) Lower
d) High
Answer: b
Clarification: Solid state combustion is the combustion process where all components are in a solid state. It occurs entirely when the melting points of the constituents are less than the adiabatic temperature leading to the lowest combustion velocities.

11. For which of the following conditions does the combustion proceeds at the highest velocity (where MP_C1 and MP_C2 are melting points of component 1 and 2 respectively)?
a) MP_C1 < T_ad < MP_C2
b) T_ad > MP_C1 and MP_C2
c) T_ad < MP_C1 and MP_C2
d) T_ad = MP_C1 and MP_C2