Tag: enzymes and catalysts

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Questions Related to enzymes and catalysts

Multiple choice enzymes and catalysts catalysis adsorption and colloids surface chemistry chemistry adsorption theory of heterogeneous catalysis

The catalyst is a substance which:

  1. increases the yield of the reaction

  2. increases the speed of the reaction

  3. decreases the speed of the reaction

  4. increases the speed of the reaction and remains unchanged.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Catalyst is a substance that changes (usually increases) the rate of a reaction, without being involved in the reaction. A catalyst provides large surface area to one of the reactants, providing it an exposure to be reacted upon by the other reactant.

Multiple choice enzymes and catalysts catalysis adsorption and colloids surface chemistry chemistry adsorption theory of heterogeneous catalysis

During hydrogenation reaction, H-H bond splits and hydrogen atoms are attached to Ni catalyst through through strong chemical forces.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In hydrogenation reaction, the H-H bond splits and the hydrogen atom is chemically bonded to the Ni catalyst.

Here the Ni catalyst provides the surface on which reaction takes place.

Multiple choice enzymes and catalysts catalysis adsorption and colloids surface chemistry chemistry adsorption theory of heterogeneous catalysis

During hydrogenation reaction, H-H bond splits and hydrogen atoms are attached to Ni catalyst through weak van der Waal forces.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
During the hydrogenation, the H-H bond split and the hydrogen atoms get attached to the Ni catalyst through chemical bonding.
Thus the given statement is false.
Multiple choice enzymes and catalysts catalysis adsorption and colloids surface chemistry chemistry adsorption theory of heterogeneous catalysis

Which of the following statements about catalysts is true?

  1. They increase the value of the equilibrium constant.

  2. They increase the amount of product present at equilibrium.

  3. They increase the concentration of the reactants.

  4. They are permanently altered as the reaction proceeds.

  5. They reduce the activation energy of the reaction.
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

Catalysts reduce the activation energy of the reaction by providing an alternate pathway having lower activation energy.
Thus, catalysts alter the mechanism of the reaction.

Multiple choice enzymes and catalysts catalysis adsorption and colloids surface chemistry chemistry adsorption theory of heterogeneous catalysis

Which quantity increases with the addition of a catalyst ?

  1. Standard voltaic potential

  2. Entropy

  3. Enthalpy

  4. Reaction rate

  5. Gibbs free energy
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Reaction rate increases with the addition of a catalyst .
The catalyst increases the rate of forward as well as reverse reaction.
Hence, the equilibrium is quickly attained.

Multiple choice enzymes and catalysts catalysis adsorption and colloids surface chemistry chemistry adsorption theory of heterogeneous catalysis

Find the false statement.

  1. The vapor pressure of a liquid decreases with increasing atmospheric pressure

  2. The value of an equilibrium constant is dependent on temperature

  3. The rate of a spontaneous reaction cannot be determined solely by its Gibbs free energy

  4. During a phase transition, the temperature of a substance must be constant

  5. The addition of a catalyst to a reaction at equilibrium has no net effect on the system

Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The incorrect statement is represented by option (A).
The vapour pressure of liquid depends on temperature and the mole fraction of solute. It does not depend on the atmospheric pressure.

Multiple choice enzymes and catalysts catalysis adsorption and colloids surface chemistry chemistry adsorption theory of heterogeneous catalysis

In the reaction, $2KClO _3+MnO _2+2KCl+3O _2(g)+MnO _2$, which substance acts as catalyst?

  1. $O _2$
  2. $KClO _3$
  3. $MnO _2$

  4. KCl
  5. $O _2$ in the $MnO _2$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The catalyst used for the decomposition of potassium chlorate to oxygen is manganese dioxide $\displaystyle  MnO _2$.
In the reaction $\displaystyle 2KClO _3+MnO _2 \rightarrow 2KCl+3O _2(g)+MnO _2 $, we see that $\displaystyle  MnO _2$ is present on the reactant side as well as on the product side. Hence, it is a catalyst. We can rewrite the same reaction as: $\displaystyle 2KClO _3  \xrightarrow {MnO _2} 2KCl+3O _2(g)$. 

Multiple choice enzymes and catalysts catalysis adsorption and colloids surface chemistry chemistry adsorption theory of heterogeneous catalysis

Among the following which of the following statements is true?

  1. A catalyst cannot lower the activation energy.

  2. A catalyst can lower the activation energy

  3. A catalyst affect only the activation energy of the forward reaction

  4. A catalyst affects only the activation energy of the reverse reaction

  5. A calatyst is permanently changed after the activation energy is released
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A catalyst can lower the activation energy. It provides an alternate path for lower activation energy.

Multiple choice enzymes and catalysts catalysis adsorption and colloids surface chemistry chemistry adsorption theory of heterogeneous catalysis

After the addition of a catalyst to an exothermic reaction, what happens?
I. The catalyst speeds up the reaction.
II. The catalyst slows down the reaction.
III. The catalyst increases the amount of product formed.

  1. I only

  2. II only

  3. I and II only

  4. II and III only

  5. I, II and III
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

After the addition of a catalyst to an exothermic reaction, the reaction speeds up. However, the amount of product formed does not increases.
A catalyst increases the rate of forward and forward reaction to equal extent. However it does not affects the value of the equilibrium constant.

Multiple choice enzymes and catalysts catalysis adsorption and colloids surface chemistry chemistry adsorption theory of heterogeneous catalysis

Which of the following is not true about a catalyst?

  1. A catalyst causes a reaction to proceed at a faster rate.

  2. A catalyst lowers the activation energy of a reaction.

  3. A catalyst affects the rate of both the forward and the reverse reaction.

  4. A catalyst increases the rate constant of a reaction.

  5. A catalyst increases the equilibrium constant of a reaction.
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

A catalyst does increases the equilibrium constant of a reaction.
Thus, a catalyst does not affect the position of equilibrium.