Tag: surface chemistry

Questions Related to surface chemistry

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 

Show answer
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

Show answer
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

Show answer
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.

Which of the following statements about catalyst is incorrect?

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

  1. They have no effect on the value of the equilibrium constant

  2. They increase the amount of product present at equilibrium

  3. They provide an alternate pathway for effective collisions

  4. They lower the activation energy

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Correct Option: B

Which of the following statements does not accurately describe the action of 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:

Option E is the correct answer.

A catalyst does not really increase the equilibrium constant of a reaction. It just increases\decreases the rate of the reaction by lowering\raising its activation energy.

A catalyst:

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

  1. changes $\Delta G$ for an equation

  2. acts by increasing the rate of the forward reaction more than the reverse reaction

  3. raises the equilibrium constant of a system

  4. may have a molecular weight as low as $1$ or higher than $200,000$

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Correct Option: D
Explanation:

Gibbs free energy change is a state function which does not depend upon the path taken by the reaction whereas catalyst change path by lowering activation energy.

Catalysts increase the rate of the reaction but have no effect on the yield and catalysts speed up both forward and reverse reaction hence it doesn't change equilibrium constant.

Catalyst doesn't need to be so bulky otherwise instead of fastening the reactions it decreases the speed of reaction. But its weight can be as low as 1 or as high as 200000.

What can cause a decrease in activation energy?

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

  1. An increase in the reactant concentration

  2. An increase in the temperature

  3. A decrease in pressure

  4. Catalysts

Show answer
Correct Option: D
Explanation:

Option D is the correct answer.

Catalysts decrease the activation energy required for a chemical reaction and increase the rate of the reaction.