Tag: adsorption theory of heterogeneous catalysis

Questions Related to adsorption theory of heterogeneous catalysis

Which are not examples of autocatalysis?

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

  1. Breakdown of atomic fuel in reactor.

  2. Shock decomposition of glycerol trinitrate.

  3. ZSM-5 used to convert alcohol in petrol.

  4. Storage of chloroform along with little ethanol.

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Correct Option: A,C,D
Explanation:

A chemical reaction is said to have undergone autocatalysis if the reaction product itself is the catalyst for that reaction.
Shock decomposition of glycerol trinitrate is autocatalysis due to the mixture of gases which acts as autocatalyst. The reaction is as follows:
$4C _3 H _5 (ONO _2) _3 \rightarrow 12CO _2 + 10H _2O + 6N _2 +O _2$

Select the correct statement(s).

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

  1. Enzyme catalysed reactions are highly specific

  2. Enzyme catalysed reactions are highly susceptible to $pH$ and temperature

  3. Decomposition of glyceryl trinitrate is an example of autocatalysis

  4. The acid hydrolysis and alkaline hydrolysis of ester are reversible

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Correct Option: A,B,C

Which of the following statements is/are correct ?

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

  1. The efficiency of a heterogeneous catalyst depends upon its surface area.

  2. Catalyst operates by providing alternate path for the reaction that involves a lower activation energy.

  3. Catalyst lowers the energy of activation of the forward direction without affecting the energy of activation of the backward direction

  4. Catalyst does not affect the overall enthalpy change of the reaction.

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Correct Option: A,B,D
Explanation:
  • A catalyst that is in a separate phase from the reactants is said to be a heterogeneous, or contact, catalyst. An example of heterogeneous catalysis is the use of finely divided platinum to catalyze the reaction of carbon monoxide with oxygen to form carbon dioxide. The efficiency of a heterogeneous catalyst depends on the surface area, more the surface area more easier the catalysis occurs.
  • Collisions only result in a reaction if the particles collide with certain minimum energy called the activation energy for the reaction. A catalyst provides an alternative route for the reaction with lower activation energy. It does not "lower the activation energy of the reaction".
  • Lowering the Activation Energy of a Reaction by a Catalyst. The only effect of the catalyst is to lower the activation energy of the reaction. The catalyst does not affect the energy of the reactants or products. Thus it doesn't affect $\Delta H$.

A catalytic poison renders the catalyst ineffective because:

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

  1. It is preferentially occupy surface of the catalyst.

  2. It adsorbs the molecules of the reactants.

  3. It combines chemically with the catalyst.

  4. It combines with one of the reactants.

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Correct Option: A
Explanation:

The poison is adsorbed in the surface of the catalyst and hence the catalyst cannot contribute to the reaction and even poisoning can react chemically with the catalyst.
Hence option A is correct.

A catalyst in finely divided state is more efficient because in this state_______.

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

  1. It has got large activation energy

  2. It can react with one reactant more effectively

  3. It has large surface area

  4. All of the above

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Correct Option: C
Explanation:

A catalyst in finely divided state is more efficient because in this state it has large surface area.
Higher is the surface area, higher is the catalytic efficiency and vice versa.

Decrease in activation energy is due to :

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

  5. $\displaystyle pH$

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Correct Option: D
Explanation:

Catalysis is the increase in the rate of a chemical reaction due to the participation of an additional substance called a catalyst. With a catalyst, reactions occur faster and require less activation energy. Because catalysts are not consumed in the catalyzed reaction, they can continue to catalyze the reaction of further quantities of reactant. Often only tiny amounts are required

After the reaction is over between adsorbed reactants, it is important to create space for the other reactant molecules to approach the surface and react. The process responsible for this is known as:

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

  1. sorption

  2. desorption

  3. physisorption

  4. chemisorption

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Correct Option: B
Explanation:

After the reaction is over between adsorbed reactants, the process of desorption is important to remove products and further create space for the other reactant molecules to approach the surface and react. 

The addition of 1% alcohol to chloroform acts as a

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

  1. positive catalyst

  2. negative catalyst

  3. autocatalyst

  4. none of these

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Correct Option: B
Explanation:

Addition of 1% alcohol to chloroform acts as negative catalyst because it decreases the rate of decomposition of CHCl$ _3$.

The lowering of activation energy by catalyst is due to

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

  1. formation of adsorbed activated complex and to provide new pathway to reaction

  2. adsorption is always exothermic

  3. the adsorbed activated complex possesses lower energy level than simple activated complex

  4. all the above

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Correct Option: A
Explanation:

The lowering of activation energy by catalyst is due to formation of adsorbed activated complex and to provide new pathway to reaction.

$KClO _3$ on heating decomposes  into $KCl$ and $O _2$. If some $MnO _2$ is added, the reaction goes much faster because :

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

  1. $MnO _2$ decomposes to give oxygen

  2. $MnO _2$ provides heat by reacting

  3. better contact is provided by $MnO _2$

  4. $MnO _2$ acts as a catalyst

Show answer
Correct Option: D
Explanation:

The reaction is as follows:
$2KClO _3\xrightarrow {heat} 2KCl+3O _2$
In this reaction, if $MnO _2$ is used, then the reaction become faster due to catalytic activities of $MnO _2$.

(Catalyst is a substance which lowers activation energy of reaction because it provides alternate pathway for reaction. Also, it increases the rate of backward and forward reaction with same extent. Due to this lower activation energy, equilibrium is attained faster but it doesnot change the overall enthalpy of the reaction.)