Tag: enzymes and catalysts

Questions Related to enzymes and catalysts

The catalyst is a substance which:

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

  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.

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Correct Option: D
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.

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

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

  1. True

  2. False

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Correct Option: A
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.

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

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

  1. True

  2. False

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Correct Option: B
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.

Which of the following statements about catalysts is true?

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

  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.

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Correct Option: E
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.

Which quantity increases with the addition of a catalyst ?

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

  1. Standard voltaic potential

  2. Entropy

  3. Enthalpy

  4. Reaction rate

  5. Gibbs free energy

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Correct Option: D
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.

Find the false statement.

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

  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 

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Correct Option: A
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.

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

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

  1. $O _2$

  2. $KClO _3$

  3. $MnO _2$

  4. KCl

  5. $O _2$ in the $MnO _2$

Show answer
Correct Option: C
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: $\displaystyle 2KClO _3  \xrightarrow {MnO _2} 2KCl+3O _2(g)$. 

Among the following which of the following statements is true?

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

  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

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Correct Option: B
Explanation:

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

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.

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

  1. I only

  2. II only

  3. I and II only

  4. II and III only

  5. I, II and III

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Correct Option: A
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.

Which of the following is not true about a catalyst?

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

  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.

Show answer
Correct Option: E
Explanation:

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