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

Which of the following statements is/are correct ?

  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.
Reveal answer Fill a bubble to check yourself
A,B,D Correct answer
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 $\Delta H$.
Multiple choice enzymes and catalysts catalysis adsorption and colloids surface chemistry chemistry adsorption theory of heterogeneous catalysis

A catalytic poison renders the catalyst ineffective because:

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

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

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

  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
Reveal answer Fill a bubble to check yourself
C Correct answer
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.

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

Decrease in activation energy is due to :

  1. an increase in the reactant concentration

  2. an increase in the temperature

  3. a decrease in pressure

  4. catalysts
  5. $\displaystyle pH$
Reveal answer Fill a bubble to check yourself
D Correct answer
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

Multiple choice chemistry chemical changes electrochemical reactions electrolysis and its applications electrolytic cells and electrolysis

An aqueous solution of volume 500 ml, when the reaction : $ 2Ag^+(aq) +Cu(s) \leftrightharpoons Cu^{2+}(aq) +2Ag(s) $ reached equilibrium, the concentration of $ Cu^{2+} $ ions was xM. to this solution, 500 ml of water is added.at new equilibrium , the concentration of $ Cu^{2+} $ ions would be 

  1. 2x M

  2. x M

  3. between x and 0.5 x M

  4. less than 0.5 x M
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Adding water increases the volume, which shifts the equilibrium. According to Le Chatelier's principle, the system will try to increase the number of ions. However, the dilution effect (concentration = moles/volume) dominates, leading to a decrease in concentration.

Multiple choice chemistry chemical changes electrochemical reactions electrolysis and its applications electrolytic cells and electrolysis

When an electric current is passed through an aqueous solution of the following, the concentrations of cation as well as anion will not change for (assume constant volume of the electrolytic solution)

  1. $ C _{S} CI $
  2. $ KNO _{3}$
  3. $ AgNO _{3}$
  4. $ HCI$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

KNO3 is a strong electrolyte where both K+ and NO3- ions have high reduction/oxidation potentials compared to water. During electrolysis, water is preferentially electrolyzed, leaving the concentration of K+ and NO3- ions effectively unchanged.

Multiple choice chemistry chemical changes electrochemical reactions electrolysis and its applications electrolytic cells and electrolysis

$NaCl$ is doped with $2\times { 10 }^{ -3 }$ mole % $Sr{Cl} _{2}$, the concentration of cation vacancies is

  1. $6.02\times { 10 }^{ 18 }{ mol }^{ -1 }$
  2. $1.204\times { 10 }^{ 19 }{ mol }^{ -1 }$
  3. $3.01\times { 10 }^{ 18 }{ mol }^{ -1 }$
  4. $1.204\times { 10 }^{ 21 }{ mol }^{ -1 }\quad $
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Each Sr2+ ion replaces two Na+ ions in the lattice, creating one cation vacancy to maintain charge neutrality. 2 * 10^-3 mole % means 2 * 10^-5 moles of SrCl2 per mole of NaCl. This corresponds to 2 * 10^-5 * 6.022 * 10^23 vacancies per mole, which is 1.204 * 10^19.

Multiple choice chemistry chemical changes electrochemical reactions electrolysis and its applications electrolytic cells and electrolysis

Electrolysis of a solution of $ MnSO _{4}$ in aqueous sulphuric acid is a method for the preparation of $ MnO _{2}$ as per the reaction: $ Mn^{2+}(aq)+2H _{2}O\rightarrow MnO _{2}(s)+2H^{+}(aq)+H _{2}(g).$ Passing a current of 19.3 A for 2 h gives only 52.2 g of $MNO _{2}.$ The current efficiency is (Mn = 55)

  1. 8.33 %

  2. 83.33 %

  3. 41.67 %

  4. 100 %
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Calculate theoretical yield using Faraday's laws: Q = I * t = 19.3 * 7200 = 138960 C. Moles of electrons = Q / F = 138960 / 96500 = 1.44 mol. Reaction: Mn2+ + 2H2O -> MnO2 + 4H+ + 2e-. Moles of MnO2 = 1.44 / 2 = 0.72 mol. Mass = 0.72 * 87 = 62.64 g. Efficiency = (52.2 / 62.64) * 100 = 83.33%.