Catalyst and Catalysis Questions in English

(D) Inhibitors are substances that decrease the rate of a chemical reaction by increasing the activation energy or by reacting with intermediates. In this case,acetamide acts as a negative catalyst or inhibitor for the decomposition of $H_2O_2$.

(D) catalyst is a substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change.
By increasing the rate of reaction,it effectively decreases the time required for the reaction to reach equilibrium or completion.

(A) Platinum acts as a catalyst in the oxidation of ammonia to form nitric oxide. This reaction is used in the Ostwald process for the preparation of nitric acid.
$4NH_3 + 5O_2 \xrightarrow{Pt, 750 \, ^oC} 4NO + 6H_2O$
$2NO + O_2 \to 2NO_2$
$4NO_2 + O_2 + 2H_2O \to 4HNO_3$

(D) $Platforming$ is a chemical process used in the petroleum industry where naphtha is passed over a $Platinum$ catalyst to improve the quality of gasoline. Therefore,it refers to the use of $Platinum$ as a catalyst. The correct option is $D$.

(B) Any substance which,when added to a chemical reaction,inhibits or decreases the rate of reaction is called a negative catalyst.
In $CHCl_3$,when $2$ percent ethanol is added,it prevents the oxidation of chloroform to poisonous carbonyl chloride $(COCl_2)$. Thus,ethanol acts as a negative catalyst.

(B) The $Thermite$ process does not use a catalyst. It is a self-sustaining exothermic reaction between a metal oxide and a metal powder (usually $Fe_2O_3$ and $Al$).

(B) catalyst provides an alternative reaction pathway with a lower activation energy $(E_a)$. By decreasing the activation energy,a larger fraction of reactant molecules can cross the energy barrier at a given temperature,thereby increasing the rate of reaction.

(C) According to the adsorption theory of catalysis,the catalyst provides a surface where reactant molecules get adsorbed.
This increases the local concentration of reactants on the surface of the catalyst.
Consequently,the number of effective collisions increases,and the catalyst provides an alternative pathway with lower activation energy $(E_a)$.
Therefore,the rate of reaction increases.

(D) catalyst is a substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change. $1.$ It provides an alternative pathway for the reaction with lower activation energy $(E_a)$. $2.$ By lowering the activation energy,it allows more reactant molecules to cross the energy barrier,thereby increasing the reaction rate. $3.$ Consequently,the system reaches the state of chemical equilibrium in a shorter amount of time. Therefore,both statements regarding time and activation energy are correct.

(A) Brown's catalyst is a specific form of platinum catalyst,which is $Pt/PtO_2$ (platinum oxide). It is commonly used for the hydrogenation of unsaturated compounds.

(A) catalyst is a substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change.
It provides an alternative reaction pathway with a lower activation energy.
However,a catalyst cannot initiate a reaction that is not thermodynamically feasible.
Therefore,the statement that 'a catalyst initiates the reaction' is incorrect.

(A) catalyst poison is a substance that reduces or destroys the activity of a catalyst. It works by getting adsorbed on the active sites of the catalyst surface,thereby preventing the reactant molecules from binding to these sites. Thus,the correct option is $A$.

(C) 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. Consequently,it allows the system to reach the state of equilibrium faster,but it does not affect the equilibrium position or the equilibrium constant $(K_{eq})$ of the reaction.

(C) Catalysts are called shape-selective catalysts because their catalytic reaction depends upon the pore structure of the catalyst and the size of the reactant and product molecules. $Zeolites$ are the most common examples of shape-selective catalysts. Their honeycomb-like structure allows only molecules of a certain size to enter the pores and react,making them highly selective.

(C) The oxidation of $Na_2SO_3$ by air occurs spontaneously.
However,$Na_3AsO_3$ does not undergo oxidation by air on its own.
When both are present,the oxidation of $Na_2SO_3$ induces the oxidation of $Na_3AsO_3$.
This phenomenon,where one chemical reaction induces another that would not otherwise occur,is known as $Induced \text{ } catalysis$.

(C) catalyst is a substance that increases the rate of a chemical reaction by providing an alternative pathway with lower activation energy.
It lowers the activation energy for both the forward and backward reactions to the same extent.
Therefore,it increases the rate of both the forward and backward reactions equally,allowing the system to reach equilibrium faster without changing the equilibrium constant $(K_{eq})$ or the position of equilibrium.

(B) The efficiency of a solid catalyst depends on the number of free valencies available on its surface.
These free valencies provide active sites for the adsorption of reactant molecules,which facilitates the reaction.

(A) In the process of hydrogenation of oils,$Ni$ (nickel) is used as a catalyst. To increase the efficiency of this catalyst,$Cu$ (copper) is often added as a promoter. Therefore,$Cu$ acts as a promoter for $Ni$ in the hydrogenation of oils.

(C) 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.
However,a catalyst does not alter the Gibbs free energy change $(\Delta G)$ of the reaction,nor does it change the equilibrium constant of the reaction.

(D) In the hydrolysis of methyl acetate,both the reactant (methyl acetate) and the catalyst (acid) are in the same phase (liquid phase).
Therefore,it is an example of homogeneous catalysis.

(A) $(1)$ When the reactants and the catalyst are in the same phase,the catalysis is called homogeneous catalysis.
$(2)$ Both the reactant $(H_2O_2)$ and the catalyst $(Br^-)$ are in the aqueous $(aq)$ phase.
$(3)$ Therefore,it is an example of homogeneous catalysis.

(B) In homogeneous catalysis,the reactants and the catalyst are in the same phase (usually liquid or gas).
In the contact process,$SO_2$ (gas) and $O_2$ (gas) react in the presence of $V_2O_5$ (solid) to form $SO_3$ (gas). This is an example of heterogeneous catalysis.
In the chamber process,$NO$ (gas) acts as a catalyst for the oxidation of $SO_2$ (gas) to $SO_3$ (gas),which is homogeneous.
Hydrolysis of sugar in the presence of acid is homogeneous.
Decomposition of $KClO_3$ (solid) in the presence of $MnO_2$ (solid) is heterogeneous,but the question asks for the best fit among the options provided. The contact process is the classic textbook example of heterogeneous catalysis.

(D) The correct answer is $D$.
In the Haber process for the industrial preparation of ammonia $(NH_3)$,finely divided iron $(Fe)$ is used as a catalyst,and molybdenum $(Mo)$ is used as a promoter.
$Ni$ (Nickel) is typically used as a catalyst in the hydrogenation of oils,not in the synthesis of ammonia.
Therefore,the statement '$Ni$ is used as a catalyst in the preparation of ammonia' is incorrect.

(D) catalyst is a substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change.
$1$. It alters the rate of reaction by providing an alternative pathway with lower activation energy.
$2$. It helps in reaching the equilibrium state faster,but it does not change the equilibrium constant.
$3$. $A$ catalyst cannot initiate a reaction that is thermodynamically impossible.
$4$. It does not affect the average kinetic energy of the molecules,as that is a function of temperature.
Therefore,options $A$,$B$,and $C$ are characteristics,while $D$ is not.

(C) The $V_2O_5$ catalyst is used in the Contact process for the manufacture of sulfuric acid $(H_2SO_4)$.
The Haber-Bosch process for the manufacture of ammonia $(NH_3)$ uses iron $(Fe)$ as a catalyst with molybdenum $(Mo)$ as a promoter.
Therefore,the pair $V_2O_5 :$ Haber-Bosch process is incorrectly matched.

(D) catalyst is a substance that alters the rate of a chemical reaction without itself undergoing any permanent chemical change. It can either increase (positive catalyst) or decrease (negative catalyst) the rate of the reaction. Therefore,the most accurate statement is that it alters the rate of the reaction.

(A) 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 or mechanism that has a lower activation energy $(E_a)$.
Therefore,the statement that it does not change the activation energy is incorrect.
Catalysts often form temporary intermediate complexes with reactants to facilitate the reaction,and enzyme catalysis is known for being highly specific.

(A) 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 on the surface of the catalyst.
$3$. Occurrence of a chemical reaction on the catalyst surface through the formation of an intermediate.
$4$. Desorption of reaction products from the surface.
$5$. Diffusion of reaction products away from the surface.
The adsorption of reactants on the active sites of the catalyst increases the local concentration of reactants on the surface,which increases the frequency of collisions and thus the rate of reaction. Additionally,the catalyst provides an alternative pathway with lower activation energy.

(B) $ZSM-5$ is a type of zeolite catalyst used in the petrochemical industry.
It is specifically used to convert alcohols (such as methanol) directly into gasoline (petrol) by dehydration,which gives a mixture of hydrocarbons.

(B) In the Haber process,the reaction is: $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$.
Here,finely divided $Fe$ is used as a catalyst to increase the rate of reaction.
$Mo$ (Molybdenum) is used as a promoter to increase the efficiency of the $Fe$ catalyst.
Therefore,$Fe$ acts as a catalyst and $Mo$ acts as a promoter.

(B) In the contact process for the manufacture of $H_2SO_4$,the oxidation of $SO_2$ to $SO_3$ is catalyzed by platinized asbestos.
Since the reactant ($SO_2$ and $O_2$ gases) and the catalyst (solid platinized asbestos) are in different physical states,it is an example of heterogeneous catalysis.

(B) In the contact process for the manufacture of $H_2SO_4$,the oxidation of $SO_2$ to $SO_3$ is catalyzed by platinum $(Pt)$ or vanadium pentoxide $(V_2O_5)$.
$As_2O_3$ (arsenic oxide) present as an impurity acts as a catalytic poison for the platinum catalyst,as it binds to the active sites of the catalyst and reduces its efficiency.

(A) 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 accelerates both the forward and backward reactions to the same extent,thereby allowing the system to reach equilibrium faster.
However,a catalyst does not alter the position of the equilibrium or the equilibrium constant $(K_{eq})$.
Therefore,the statement that a catalyst changes the equilibrium point is incorrect.

(A) The decomposition of hydrogen peroxide $(H_2O_2)$ is a catalytic reaction.
Acetanilide acts as a negative catalyst or inhibitor for this reaction.
It slows down the rate of decomposition of $H_2O_2$ by reacting with the intermediate species or by deactivating the catalyst present in the system.
Therefore,it is classified as an inhibitor.

(B) In the contact process for the manufacture of $SO_3$,$Pt$ acts as a catalyst.
$As_2O_3$ (Arsenic oxide) is present as an impurity in the reactant gases.
This $As_2O_3$ adsorbs on the surface of the $Pt$ catalyst,thereby reducing its catalytic activity.
Therefore,$As_2O_3$ acts as a catalytic poison.

(D) Zeolites are aluminosilicates with a three-dimensional network structure.
They are microporous in nature, which allows them to act as molecular sieves.
The general chemical formula for zeolites is $M_{x/n}[(AlO_2)_x(SiO_2)_y] \cdot mH_2O$.
Due to their structure, they possess pore sizes typically ranging from $260 \ pm$ to $740 \ pm$.
Therefore, all the given statements are correct.

(B) In $Autocatalysis$,one of the products formed in the reaction acts as a catalyst for the same reaction.
For example,the hydrolysis of ethyl acetate: $CH_3COOC_2H_5 + H_2O \rightarrow CH_3COOH + C_2H_5OH$.
Here,the acetic acid $(CH_3COOH)$ produced acts as an autocatalyst.

(A) Zeolites are shape-selective catalysts that are widely used in the petrochemical industry for cracking of hydrocarbons and isomerization reactions. $ZSM-5$ is a well-known zeolite catalyst used to convert alcohols directly into gasoline. Therefore,the correct option is $A$.

(C) The reaction between potassium permanganate $(KMnO_4)$ and oxalic acid $(H_2C_2O_4)$ in the presence of sulfuric acid $(H_2SO_4)$ is given by:
$2KMnO_4 + 3H_2SO_4 + 5H_2C_2O_4 \rightarrow K_2SO_4 + 2MnSO_4 + 8H_2O + 10CO_2$.
In this reaction,$Mn^{2+}$ ions are produced as one of the products.
These $Mn^{2+}$ ions increase the rate of the reaction,a phenomenon known as autocatalysis.
Therefore,$Mn^{2+}$ acts as an autocatalyst.

(D) Zeolites are hydrated sodium aluminosilicates which have a porous structure.
They are used as water softeners because they exchange $Na^+$ ions with $Ca^{2+}$ and $Mg^{2+}$ ions present in hard water.
They act as cation exchangers due to their ion-exchange properties.
They are also widely used as shape-selective catalysts in the petrochemical industry (e.g.,$ZSM$-$5$).
Therefore,all the given statements are correct.

(A) The reaction between oxalic acid $(H_2C_2O_4)$ and potassium permanganate $(KMnO_4)$ 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 for the reaction,which increases the rate of the reaction as the concentration of $Mn^{2+}$ increases.
Therefore,the reaction proceeds slowly at the start and becomes very rapid once some $Mn^{2+}$ is formed.
This phenomenon is known as autocatalysis.

(B) In a reaction,if one of the products acts as a catalyst for the reaction,the phenomenon is known as $Autocatalysis$.
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) In the Haber process,$Fe$ is used as a catalyst.
In the Friedel-Crafts reaction,anhydrous $AlCl_3$ is used as a catalyst.
In the hydrogenation of oils,$Ni$ (Nickel) is used as a catalyst,not $Fe$.
In the contact process,$V_2O_5$ is used as a catalyst for the oxidation of $SO_2$ to $SO_3$.
Therefore,the statement regarding the hydrogenation of oils is incorrect.

(B) Raney nickel is a fine-grained solid catalyst composed of nickel derived from a nickel-aluminum alloy.
It is prepared by treating the nickel-aluminum alloy with a concentrated aqueous solution of sodium hydroxide $(NaOH)$.
The aluminum dissolves in the $NaOH$ solution,leaving behind a highly porous,finely divided nickel residue known as Raney nickel.
The reaction is: $2Al + 2NaOH + 6H_2O \rightarrow 2Na[Al(OH)_4] + 3H_2$.