Unit Processes Question Bank on “Kinetic and thermodynamics of hydrogenation reaction”.
1. What is meant by spontaneous reaction?
a) Reaction needing heat
b) Proceeds on own
c) Catalyst help
d) Change in temperature
Answer: b
Clarification: All spontaneous reactions, i.e., those proceeding of their own accord and in the absence of any electrical influences, such as magnetic or electrostatic forces, or various forms of radiation, are attended by a free-energy decrease.
2. Fill in the blank: Compound with the ______ free energy is the more stable.
a) Lower
b) High
c) Moderate
d) None of the mentioned
Answer: a
Clarification: The compound with the lower free energy is the more stable of the two under the experimental conditions chosen.
3. In higher olefins, what happens to the free energy on hydrogenation?
a) Increases
b) No change
c) Decreases
d) None of the mentioned
Answer: c
Clarification: For the higher olefins, the free-energy decrease on hydrogenation is very small and approaches zero.
4. Why is it better to have reduction at low temperatures?
a) Good yield
b) No side reaction
c) Equilibrium
d) All of the mentioned
Answer: d
Clarification: It is desirable to carry out such a reduction at lower temperatures for two pertinent reasons: (1) the equilibrium yield is better, (2) decomposition or side reactions are less likely to be troublesome.
5. Hydrogenation reactions are reversible.
a) True
b) False
Answer: a
Clarification: Most hydrogenation reactions are reversible reactions.
6. Destructive hydrogenation is best to occur at which temperature?
a) Higher
b) Moderate
c) Lower
d) None of the mentioned
Answer: a
Clarification: Destructive hydrogenation or hydrogenolysis would be more apt to occur at higher temperatures, for all reaction velocities are increased, and the specificity of a catalyst is, in general, markedly reduced.
7. Practically every hydrogenation reaction cannot be reversed by increasing temperature.
a) True
b) False
Answer: b
Clarification: Temperature is one of the most important variables affecting a reaction. Practically every hydrogenation reaction can be reversed by increasing temperature. It becomes necessary, then, to work at as Iowa temperature as possible where the rate of reaction will still be satisfactory. Whereas catalysts affect only the speed and course of a reaction, temperature affects the equilibrium position, the speed, and the path, or course, of a reaction.
8. What happens to the yield on increasing temperature?
a) Increases
b) No change
c) Decreases
d) None of the mentioned
Answer: c
Clarification: In general, then, increasing temperature adversely affects the equilibrium position, so that the maximum ultimate yield is decreased; but it affects favourably the speed of a reaction, so that in a given time a greater quantity of product can be obtained.
9. What happens to the rate of reaction on increasing pressure?
a) Increases
b) Decreases
c) No change
d) None of the mentioned
Answer: a
Clarification: Pressure, like temperature, can affect the rate of reaction as well as the equilibrium position. The rate of reaction is generally increased by increasing pressure, because a gas phase is usually present, and increased pressure gives increased concentration.
10. The time needed for a hydrogenation reaction depends on what?
a) Catalyst
b) Temperature
c) Pressure
d) All of the mentioned