Catalyst and Catalysis Questions in English

(C) Water gas is a mixture of $CO$ and $H_2$.
The catalytic hydrogenation of carbon monoxide to produce methanol is carried out using a mixture of $ZnO$ and $Cr_2O_3$ as the catalyst.
The reaction is: $[CO + H_2] + H_2 \xrightarrow{ZnO + Cr_2O_3} CH_3OH$.

(D) Shape-selective catalysis is a type of catalysis that depends on the pore structure of the catalyst and the size of the reactant and product molecules. Zeolites are the most common shape-selective catalysts.
They are aluminosilicates with a general formula $M_{x/n}[(AlO_2)_x \cdot (SiO_2)_y] \cdot mH_2O$.
Zeolites are widely used in the petrochemical industry for the conversion of alcohols to gasoline (using $ZSM$-$5$) and in the polymerisation of ethylene.
Therefore,both $(a)$ and $(c)$ involve shape-selective catalysis.

(B) The ability of a catalyst to accelerate the chemical reaction is known as its activity.
Degree of acceleration can be as high as $10^{10}$ times in certain reactions.

(A) catalyst decreases the activation energies of both the forward and backward reactions by the same amount.
Therefore,it speeds up both the forward and backward reactions at the same rate.
As a result,the equilibrium constant $(K_{eq})$ remains unaffected by the presence of a catalyst at a given temperature.
Thus,the statement that the equilibrium constant changes is incorrect.

(D) The correct matches are as follows:
$A. TiCl_4$ is used in $ii. \text{Ziegler-Natta polymerization}$.
$B. PdCl_2$ is used in $i. \text{Wacker process}$.
$C. CuCl_2$ is used in $iv. \text{Deacon's process}$.
$D. V_2O_5$ is used in $iii. \text{Contact process}$.
Therefore,the correct sequence is $A-ii, B-i, C-iv, D-iii$.

(B) In the Haber's process for the synthesis of ammonia,finely divided iron $(Fe)$ acts as the catalyst.
$Mo$ (Molybdenum) is added to the reaction mixture to act as a catalytic promoter,which increases the efficiency of the iron catalyst.

(A) The reaction between acidified $KMnO_4$ and oxalic acid is given by:
$2MnO_4^- + 5H_2C_2O_4 + 6H^+ \rightarrow 2Mn^{2+} + 10CO_2 + 8H_2O$.
In this reaction,$Mn^{2+}$ ions are produced as a product.
These $Mn^{2+}$ ions act as an autocatalyst,meaning they increase the rate of the reaction as their concentration increases.
Therefore,the reaction is slow initially but becomes rapid as the concentration of $Mn^{2+}$ increases.

(C) The correct matches are as follows:
$A$. Haber's process for ammonia uses $Fe$ as a catalyst $(A-Q)$.
$B$. Oswald's process for $HNO_3$ uses $Pt$ gauge as a catalyst $(B-S)$.
$C$. Contact process for $H_2SO_4$ uses $V_2O_5$ as a catalyst $(C-R)$.
$D$. Cracking of hydrocarbons uses Zeolite as a catalyst $(D-P)$.
Therefore,the correct sequence is $A-Q, B-S, C-R, D-P$.

(D) catalyst is a substance that increases the rate of a chemical reaction by providing an alternative pathway with a lower activation energy $(E_a)$.
$1$. It does not alter the Gibbs energy $(\Delta G)$ of the reaction.
$2$. It does not change the equilibrium position because it accelerates both the forward and backward reactions to the same extent.
$3$. Since it provides a new pathway with lower activation energy,the activation energy of the reaction is indeed altered (lowered).
Therefore,the statement that the activation energy remains unaltered is incorrect.

(D) catalyst provides an alternative reaction pathway with a lower activation energy $(E_a)$.
This increases the rate constant $(k)$ and consequently the rate of the reaction.
However,the enthalpy of reaction $(\Delta H)$ is a state function that depends only on the initial and final states of the reactants and products.
Therefore,the enthalpy of reaction remains unchanged by the presence of a catalyst.

(B) In the contact process for the manufacture of $H_2SO_4$,$SO_2$ is oxidized to $SO_3$ using a catalyst.
Platinized asbestos (platinum metal deposited on asbestos) acts as a solid catalyst for the gaseous reactants ($SO_2$ and $O_2$).
Since the catalyst is in a different physical state (solid) than the reactants (gases),this is an example of heterogeneous catalysis.

$(A)$ $V_2O_5$ is used as a catalyst in the Contact process for the conversion of $SO_2$ to $SO_3$ $(A-i)$.
$Ni$ is used as a catalyst for the hydrogenation of oils $(B-ii)$.
$MnO_2$ acts as a catalyst in the decomposition of $KClO_3$ to prepare $O_2$ $(C-iii)$.
$Fe$ is used as a catalyst in the Haber's process for the synthesis of ammonia $(D-iv)$.
Therefore, the correct matching is $A-i, B-ii, C-iii, D-iv$.

(A) The reaction between $KMnO_4$ and oxalic acid is given by: $2MnO_4^- + 5C_2O_4^{2-} + 16H^+ \rightarrow 2Mn^{2+} + 10CO_2 + 8H_2O$.
In this reaction,$Mn^{2+}$ ions are produced as a product.
These $Mn^{2+}$ ions act as an auto-catalyst for the reaction.
Initially,the concentration of $Mn^{2+}$ is very low,so the reaction proceeds slowly.
As the reaction progresses,the concentration of $Mn^{2+}$ increases,which accelerates the rate of the reaction.
This phenomenon,where a product of the reaction acts as a catalyst,is known as auto-catalysis.

(A) $ZSM-5$ is a shape-selective zeolite catalyst that converts alcohols directly into gasoline (petrol) by dehydrating them to form a mixture of hydrocarbons.

(A) The catalytic reaction that depends upon the pore structure of the catalyst and the size of the reactant and product molecules is called shape-selective catalysis.
Zeolites are good shape-selective catalysts because of their honeycomb-like structures.
Zeolites are widely used as catalysts in petrochemical industries for the cracking of hydrocarbons and isomerisation.
An important zeolite catalyst used in the petroleum industry is $ZSM-5$.

(A) The reaction between $KMnO_4$ and oxalic acid $(H_2C_2O_4)$ in an acidic medium is given by: $2MnO_4^- + 5H_2C_2O_4 + 6H^+ \rightarrow 2Mn^{2+} + 10CO_2 + 8H_2O$.
In this reaction,$Mn^{2+}$ ions are produced as a product.
These $Mn^{2+}$ ions act as an autocatalyst,meaning they increase the rate of the reaction as their concentration increases.
Initially,the concentration of $Mn^{2+}$ is very low,so the reaction is slow.
As the reaction proceeds,more $Mn^{2+}$ is formed,which accelerates the reaction,making the decolourisation instantaneous.

(A) In heterogeneous catalysis,the catalyst is in a different phase from the reactants.
$1$. Lead chamber process: Uses $NO$ (gas) as a catalyst for the oxidation of $SO_2$ (gas) to $SO_3$ (gas). Since both the reactants and the catalyst are in the gaseous phase,it is a homogeneous catalysis.
$2$. Haber's process: Uses $Fe$ (solid) as a catalyst for the reaction between $N_2$ (gas) and $H_2$ (gas). This is heterogeneous.
$3$. Ostwald's process: Uses $Pt$ (solid) as a catalyst for the oxidation of $NH_3$ (gas). This is heterogeneous.
$4$. Contact process: Uses $V_2O_5$ (solid) as a catalyst for the oxidation of $SO_2$ (gas). This is heterogeneous.
Therefore,the Lead chamber process is not a heterogeneous adsorption process.

(B) heterogeneous catalytic reaction involves a catalyst in a different phase from the reactants.
$A$. Ostwald's process uses a $Pt$ catalyst (solid) for the oxidation of $NH_3$ (gas),which is heterogeneous.
$B$. Combustion of coal is a spontaneous oxidation reaction that does not require a catalyst.
$C$. Hydrogenation of vegetable oils uses a $Ni$ catalyst (solid) for liquid oils and $H_2$ (gas),which is heterogeneous.
$D$. Haber's process uses an $Fe$ catalyst (solid) for $N_2$ and $H_2$ (gases),which is heterogeneous.
Therefore,the combustion of coal is not a catalytic reaction at all.

(A) $V_2O_5$ is used as a catalyst in the Contact process for the manufacture of $H_2SO_4$.
$TiCl_4/Al(Me)_3$ is the Ziegler-Natta catalyst used in the polymerization of ethene to form Polyethylene.
$PdCl_2$ is used in the Wacker process for the oxidation of ethene to Ethanal.
Iron oxide is used as a catalyst in the Haber process for the production of $NH_3$.
Therefore,the correct matching is: $(a-iii, b-i, c-ii, d-iv)$.

(B) Hydrogenation is a process where hydrogen is added to unsaturated fats,such as vegetable oils,to convert them into saturated fats (solids) at room temperature.
This process is typically carried out in the presence of a finely divided metal catalyst.
Nickel $(Ni)$ is the most commonly used catalyst for the hydrogenation of vegetable oils.
Therefore,the correct option is $B$.

(A) The reaction between $KMnO_4$ and oxalic acid $(H_2C_2O_4)$ in an acidic medium produces $Mn^{2+}$ ions.
Initially,the concentration of $Mn^{2+}$ is very low,making the reaction slow.
As the reaction proceeds,$Mn^{2+}$ ions are produced,which act as an autocatalyst for the reaction.
This autocatalytic effect significantly increases the rate of reaction,making the decolorization instantaneous after some time.

(C) In the industrial Haber process for the production of ammonia $(NH_3)$,finely divided iron $(Fe)$ is used as a catalyst,and molybdenum $(Mo)$ is used as a promoter to increase the efficiency of the catalyst.

(B) The distribution of free bonds on the catalyst surface is not uniform.
These are crowded at the 'peaks','cracks',and corners of the catalyst.
The catalytic activity due to adsorption of reacting molecules is maximum at these spots.
These are,therefore,referred to as the active centers.
The active centers,i.e.,free valencies,increase the rate of reaction not only by increasing the concentration of the reactants but also by activating the molecule adsorbed at two such centers by stretching it.

(D) Zeolites are microporous aluminosilicate minerals that act as shape-selective catalysts. Their catalytic activity depends on the size and shape of their $pores$,$apertures$ (openings),and $cavities$ (cages),which allow only specific molecules to enter or exit the active sites.

(C) catalyst is a substance that alters the rate of a chemical reaction without itself undergoing any permanent chemical change.
$1$. $A$ catalyst cannot initiate a reaction that is not thermodynamically feasible.
$2$. $A$ negative catalyst (inhibitor) increases the activation energy; it does not decrease it.
$3$. $A$ catalyst provides an alternative pathway with lower activation energy,but it does not change the initial and final energy states of the reactants and products; hence,the enthalpy of reaction $(\Delta H)$ remains unchanged.
$4$. In a reversible reaction,a catalyst increases the rate of both the forward and backward reactions to the same extent,thereby helping the system reach equilibrium faster without changing the equilibrium constant.

(C) In autocatalysis,one of the products of the reaction acts as a catalyst for the same reaction. This leads to an increase in the rate of reaction as the concentration of the product increases.

(B) The $Haber$ process uses iron as a catalyst for the synthesis of ammonia.
The $Ostwald$ process uses platinum/rhodium gauze as a catalyst for the production of nitric acid.
The $Contact$ process uses vanadium pentoxide $(V_2O_5)$ as a catalyst for the production of sulfuric acid.
The $Thermite$ process is a pyrotechnic composition of metal powder and metal oxide,which produces an exothermic reaction without the use of a catalyst.

(B) Homogeneous catalysis is a process where the catalyst and the reactants are in the same physical state (phase).
In option $B$,the reactants $CH_3COOH$ and $C_2H_5OH$ are in the liquid phase,and the catalyst $H^+$ (from an acid like $H_2SO_4$) is also in the liquid phase.
In option $A$,$Ni$ is a solid catalyst while the reactants are liquid/gas.
In option $D$,$Fe$ is a solid catalyst while the reactants are gases.
Therefore,option $B$ represents homogeneous catalysis.

(C) catalyst is a substance that increases the rate of a reaction without itself undergoing any permanent chemical change.
It works by providing an alternative reaction pathway with a lower activation energy $(E_a)$.
Since the catalyst lowers the activation energy for both the forward and backward reactions to the same extent,it does not change the overall enthalpy change $(\Delta H)$ of the reaction.
Option $C$ is incorrect because a catalyst decreases the activation energy for both the forward and backward reactions,not just the forward reaction.

(D) According to the adsorption theory of catalysis,the mechanism involves the following steps:
$1$. Diffusion of reactants to the surface of the catalyst.
$2$. Adsorption of reactant molecules onto the surface of the catalyst.
$3$. Formation of an intermediate on the surface,which leads to a decrease in the activation energy of the reaction.
$4$. Desorption of products from the surface.
$5$. Diffusion of products away from the surface.
By adsorbing reactant molecules onto the active sites,the local concentration of reactants increases,which enhances the probability of collision and reaction,effectively lowering the activation energy path. Therefore,the correct statement is that the concentration of reactant molecules increases at the active sites of the catalyst.

(C) The reaction between oxalic acid $(H_2C_2O_4)$ and acidic potassium permanganate $(KMnO_4)$ is given by:
$2MnO_4^- + 5H_2C_2O_4 + 6H^+ \rightarrow 2Mn^{2+} + 10CO_2 + 8H_2O$
In this reaction,the $Mn^{2+}$ ions produced act as a catalyst for the reaction.
Since one of the products of the reaction acts as a catalyst for the same reaction,it is known as an autocatalyst.

(A) Catalytic poisons are substances that decrease the activity of a catalyst. They work by being preferentially adsorbed on the active sites of the catalyst surface. This prevents the reactant molecules from reaching the active sites,thereby rendering the catalyst ineffective. Therefore,the correct reason is that they are adsorbed on the catalyst surface first.

(B) In autocatalysis,one of the products of the reaction acts as a catalyst for the same reaction.
As the reaction proceeds,the concentration of the product increases,which in turn increases the rate of the reaction.
For example,the hydrolysis of an ester: $CH_3COOC_2H_5 + H_2O \rightarrow CH_3COOH + C_2H_5OH$.
Here,the acetic acid $(CH_3COOH)$ produced acts as an autocatalyst.

(C) catalyst is a substance that alters the rate of a chemical reaction without itself undergoing any permanent chemical change. It works by providing an alternative reaction pathway with a lower activation energy,thereby increasing the rate of reaction. It does not change the equilibrium constant or the equilibrium position of a reversible reaction,nor does it initiate a reaction that is not thermodynamically feasible.

(D) catalyst is a substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change.
It works by providing an alternative reaction pathway with a lower activation energy $(E_a)$.
It does not change the equilibrium constant,the amount of products,or the enthalpy change $(\Delta H)$ of the reaction.

(D) The adsorption theory of catalysis is primarily applicable to $Heterogeneous$ $catalysis$.
In this process,the reactant molecules are adsorbed on the surface of the solid catalyst,which increases the concentration of reactants at the surface and facilitates the reaction by providing an alternative path with lower activation energy.

(D) substance that increases the activity of a catalyst is called a promoter.
For example,in the Haber process for the manufacture of ammonia $(N_2 + 3H_2 \rightleftharpoons 2NH_3)$,iron $(Fe)$ acts as a catalyst,while molybdenum $(Mo)$ acts as a promoter to increase the efficiency of the iron catalyst.

(B) negative catalyst is a substance that decreases the rate of a chemical reaction by increasing the activation energy required for the reaction to proceed. Therefore,it slows down the reaction rate.

(D) catalyst is a substance that alters the rate of a chemical reaction without itself undergoing any permanent chemical change.
It does not change the nature of the products,nor does it necessarily increase the rate (it can also decrease it,as in negative catalysis).
Crucially,a catalyst is not consumed in the reaction,meaning it can be recovered at the end of the process.

(C) $V_2O_5$ is used as a catalyst in the contact process for the manufacture of $SO_3$ and subsequently $H_2SO_4$.
In the Haber-Bosch process for the manufacture of $NH_3$,finely divided $Fe$ with molybdenum as a promoter is used.
Therefore,the match $V_2O_5 :$ Haber-Bosch process is incorrect.

(A) catalyst works by providing an alternative reaction pathway with lower activation energy. The reaction occurs on the surface of the catalyst. By converting the catalyst into a finely divided form,the total surface area available for the reactant molecules to adsorb increases significantly. This leads to a higher rate of reaction,making the catalyst more effective.

(A) $i. Na_{2}O$ is used in the oxidation of $SO_{2}$ to $SO_{3}$ in the contact process for the manufacture of $H_{2}SO_{4}$ $(i-c)$.
$ii. TiCl_{4} + Al(CH_{3})_{3}$ is the Ziegler-Natta catalyst used for the polymerisation of ethylene $(ii-d)$.
$iii. PdCl_{2}$ is used in the Wacker process for the oxidation of ethyne to ethanal $(iii-a)$.
$iv. \text{Nickel complexes}$ are used for the polymerisation of alkynes $(iv-b)$.
Thus,the correct matching is $i-c, ii-d, iii-a, iv-b$.

(C) The catalytic activity of transition metals for hydrogenation reactions depends on the strength of adsorption of reactants on the metal surface.
If the adsorption is too weak,the reactants do not stay on the surface long enough to react.
If the adsorption is too strong,the surface becomes blocked and the product cannot desorb.
Group $7-9$ elements possess the optimal strength of adsorption for reactants,which leads to maximum catalytic activity.
Therefore,both the assertion and the reason are true,and the reason correctly explains the assertion.

(N/A) Heterogeneous catalysis is a process where the catalyst and reactants exist in different phases. The mechanism is explained by the adsorption theory,which involves the following steps:
$i$. Adsorption of reactant molecules onto the surface of the solid catalyst.
$ii$. Occurrence of a chemical reaction on the surface through the formation of an intermediate.
$iii$. Desorption of the reaction products from the catalyst surface.
$iv$. Diffusion of the products away from the catalyst surface.
In this process,the solid catalyst surface provides active sites where the concentration of gaseous reactants increases,thereby increasing the rate of reaction. Once the reaction occurs,the products have a lower affinity for the surface and are desorbed,freeing the active sites for further reactant molecules.

(N/A) $(i)$ Oxidation of sulphur dioxide to form sulphur trioxide. In this reaction,$Pt$ acts as a catalyst.
$2SO_{2(g)} + O_{2(g)} \xrightarrow{Pt(s)} 2SO_{3(g)}$
$(ii)$ Formation of ammonia by the combination of dinitrogen and dihydrogen in the presence of finely divided iron $(Fe)$.
$N_{2(g)} + 3H_{2(g)} \xrightarrow{Fe(s)} 2NH_{3(g)}$
This process is called the Haber's process.
$(iii)$ Ostwald's process: Oxidation of ammonia to nitric oxide in the presence of platinum $(Pt)$.
$4NH_{3(g)} + 5O_{2(g)} \xrightarrow{Pt(s)} 4NO_{(g)} + 6H_{2}O_{(g)}$
$(iv)$ Hydrogenation of vegetable oils in the presence of nickel $(Ni)$.
$\text{Vegetable oil}_{(l)} + H_{2(g)} \xrightarrow{Ni(s)} \text{Vegetable ghee}_{(s)}$

(N/A) Activity of a catalyst:
The activity of a catalyst is its ability to increase the rate of a particular reaction. Chemisorption is the main factor in deciding the activity of a catalyst. The adsorption of reactants on the catalyst surface should be neither too strong nor too weak. It should just be strong enough to make the catalyst active.
$(b)$ Selectivity of the catalyst:
The ability of the catalyst to direct a reaction to yield a particular product is referred to as the selectivity of the catalyst. For example,by using different catalysts,we can get different products for the reaction between $H_{2}$ and $CO$.
$(i)$ $CO_{(g)} + 3H_{2(g)} \xrightarrow{Ni} CH_{4(g)} + H_{2}O_{(g)}$
$(ii)$ $CO_{(g)} + 2H_{2(g)} \xrightarrow{Cu, ZnO-Cr_{2}O_{3}} CH_{3}OH_{(g)}$
$(iii)$ $CO_{(g)} + H_{2(g)} \xrightarrow{Cu} HCHO_{(g)}$

(N/A) Zeolites are alumino-silicates that are micro-porous in nature.
Zeolites have a honeycomb-like structure,which makes them shape-selective catalysts.
They have an extended $3D$ network of silicates in which some silicon atoms are replaced by aluminium atoms,giving them an $Al-O-Si$ framework.
The reactions taking place in zeolites are very sensitive to the pores and cavity size of the zeolites.
Zeolites are commonly used in the petrochemical industry.

(N/A) catalytic reaction that depends upon the pore structure of the catalyst and the size of the reactant and product molecules is called shape-selective catalysis.
For example, catalysis by zeolites is a shape-selective catalysis.
The pore size present in zeolites ranges from $260-740 \, pm$.
Thus, molecules having a size larger than the pore size cannot enter the zeolite cavities and undergo the reaction.

(N/A) $ZSM-5$ is a type of zeolite catalyst used to convert alcohols directly into gasoline (petrol).

(N/A) Catalyst: $A$ catalyst is a substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change. For example,$MnO_{2}$ acts as a catalyst in the following reaction to increase its rate significantly:
$2KClO_{3} \xrightarrow{MnO_{2}} 2KCl + 3O_{2}$
Inhibitor: When an added substance reduces the rate of a chemical reaction,it is called an inhibitor. The term catalyst should not be used to describe an inhibitor.