Enzymes and catalysts - class-XI

Catalyst is a substance, which lowers the activation energy of reaction because it provides an alternate pathway for reaction. Also, it increases backward and forward reaction to the same extent. Due to this lower activation energy, equilibrium is attained faster.

Competitive Inhibitors belong to the category of enzymes known as reversible inhibitors. Reversible inhibitors dissociate the enzyme-inhibitor complex as soon as possible.

Competitive Inhibitor - A competitive inhibitor is any compound which closely resembles the chemical structure and molecular geometry of the substrate.

Non-competitive Inhibitor - A non-competitive inhibitor is a substance that interacts with the enzyme, but usually not at the active site. The noncompetitive inhibitor reacts either remote from or very close to the active site.

A catalyst increases rate of reacting by decreasing activation energy. and increasing the enthalpy change of the reaction

KMnO4 is a classic example of an autocatalyst in the reaction between oxalic acid and acidified potassium permanganate, where Mn2+ ions produced during the reaction catalyze the process.

Auto-catalysis is defined as the reaction that is catalyzed by one of its product.  in auto-catalysis product of reaction acts as a catalyst for the reaction.  In auto-catalysis the initial rate of reaction rises as the catalytic product is formed instead of decreasing steadily.  

In a reversible reaction, a catalyst increases the rate of the forward and backward reactions equally.
An increase in rate of reaction in forward direction by a catalyst for a reaction in equilibrium brings in an increase in concentration of products at faster rate and thus, rate of backward reaction also increases to same magnitude and the equilibrium position is not altered. In such reactions equilibrium constant does not alters.

Option (B) is correct.
Catalyst does not alter the state of equilibrium. In the presence of a catalyst, both the forward and reverse reaction rates will speed up equally, thereby allowing the system to reach equilibrium faster. The addition of a catalyst has no effect on the final equilibrium position of the reaction.

The minimum energy level necessary to permit a reaction to occur is called threshold energy.
Threshold energy is the energy level where some chemical/physical action happens. Threshold energy for production of a particle is the minimum kinetic energy a pair of traveling particles must have when they collide. The threshold energy is always greater than or equal to the rest energy of the desired particle.

Chemical equilibrium is not affected by a catalyst.
When a catalyst is used, the equilibrium is achieved faster but the value of the equilibrium constant remains unaffected.

The given statement is true.
Activation energy is always lowered by positive catalyst. This increases the rate of the reaction.

The given statement is true.
A catalyst remains unchanged chemically at the end of the reaction. It may take part in the reaction mechanism. It may be consumed in the first step and regenerated in the second step.

For a catalyst, high ionization energy is not essential.
The essential conditions include variable valency, empty orbitals and free valency on the surface.

Catalyst is a substance that changes (usually increases) the rate of a reaction, without being involved in the reaction. A catalyst provides large surface area to one of the reactants, providing it an exposure to be reacted upon by the other reactant.

In hydrogenation reaction, the H-H bond splits and the hydrogen atom is chemically bonded to the Ni catalyst.

Catalysts reduce the activation energy of the reaction by providing an alternate pathway having lower activation energy.
Thus, catalysts alter the mechanism of the reaction.

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.

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.

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: $\displaystyle 2KClO _3  \xrightarrow {MnO _2} 2KCl+3O _2(g)$. 

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, 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.

A catalyst does increases the equilibrium constant of a reaction.
Thus, a catalyst does not affect the position of equilibrium.

Catalysts increase the rate of reaction by lowering activation energy, but they do not change the position of equilibrium or the amount of product formed at equilibrium.

Option E is the correct answer.

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.

Option D is the correct answer.

Catalysts work by producing an alternative route for the reaction. This affects the forward and back reactions equally so there is not any change in equilibrium.

Further catalysts speed up both forward and reverse reactions otherwise its equilibrium constant get change which further change the equilibrium

Catalyst only alters the pathway of reaction by lowering the activation energy. They don't use in any reaction and remain unconsumed after the reaction.

Since they are lowering the activation energy so reactants easily cross the barriers and make no-spontaneous reactions occur

It is not necessary that catalysts are in the same phase with reactants such catalysis called heterogeneous catalysis.
For eg. $2SO _2(g) \xrightarrow{Pt(s)} 2SO _3(g)$

The equilibrium constant does not change in reaction by the catalyst which means that equilibrium doesn't shift in any direction. Hence option D is not correct.

A catalyst is a substance which increases the free energy change(rate of reaction) in the reaction.But is not consumed by the reaction; hence a catalyst can be recovered chemically unchanged at the end of the reaction it has been used to speed up or catalyze.

A catalyst is a substance which increases (accelerate)  the rate of reaction.But is not consumed by the reaction; hence a catalyst can be recovered chemically unchanged at the end of the reaction it has been used to speed up, or catalyze. 

All catalysts are specific for certain  reactants. A certain catalyst can react with a particular reactant only. All catalysts do not react with all reactants.
Hence option A is correct.

Edges and peaks of catalyst are the interacting sites of catalysts with the reagents as they have free valencies.So edges and peaks are effective sites of catalysts.
Hence option A is correct

The substance which decreases the rate of a chemical reaction is called inhibitor e.g. anti-oxidants are added as inhibitors to food substances to stop its spoilage from exposure oxygen. Similarly, protective coatings on metal surfaces inhibit the corrosion of metals by preventing their interaction with the air and water. An inhibitor is an opposite of a catalyst.

Purple permanganate ions are reduced in acidic solution by oxalate ions to the nearly colorless manganese(II) ions, whereas the oxalate ions are oxidized to gaseous carbon dioxide: Obviously, the $Mn^{2+}$  ions act as catalyst. The reaction rate increases gradually even when no $Mn^{2+}$ ions are added because they are formed during the reaction meaning this product autocalyzes its own formation. 

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 they also activate the molecule adsorbed at two such centers by stretching it.

The chemical substance added to another substance, to slow down a reaction or to prevent an unwanted chemical change is called inhibitor. The decomposition of hydrogen peroxide. Unwanted chemical change can be slowed down by the addition of a small amount of acetamide. The latter acts as an inhibitor.

A catalyst is the substance which speed up the chemical reaction by lowering the activation energy of reaction but it do not effects the amount of forward and backward reaction.
Hence option B is correct.

Reaction mechanism for the decomposition of nitroglycerine $4C _3H _5N _3O _9 \rightarrow 6N _2 + 12CO _2 + 10H _20 + O _2$.
This reaction is auto catalytic which is based upon internal redox chemistry.

A Lindlar catalyst is a heterogeneous catalyst which  consists of palladium deposited on calcium carbonate which is then poisoned with various forms of lead or sulphur not with $BaSO _4$ and quiniline. It is used for the hydrogenation of alkynes to alkenes.

Enzymes are biological molecules (typically proteins) that significantly speed up the rate of virtually all of the chemical reactions that take place within cells by lowering the activation energy required for the reaction. It alters the pathway but doesn't take part in the reaction.

A catalyst is a substance which speed up the chemical reaction by lowering the activation energy of reaction but it does not change the equilibrium point.

The effect of catalyst is to increase speed of reaction by lowering the activation energy
As it affect forward and backward reaction equally hence it don't change any thermodynamical aspects of reaction.
Further catalyst don't take part in reaction so it don't change the final products.

The chemical equilibrium of a reversible reaction is not influenced by the catalyst.Catalyst does not play any role in the backward reaction.

In
the tit-ration between oxalic acid and acidified potassium permanganate, the
manganous salt formed during the reaction and catalyses the reaction. The
manganous salt acts as auto catalyst because the rate of reaction depends on the manganous ions formed,so manganous ions catlyze the reaction.
Hence option C is correct.

The process which is catalyzed by one of the products is called is called auto-catalysis.The product used for the catalysis is auto catalyst.

Autocatalysis is the reaction where one of the products formed catalyzes the reaction. So in case of auto catalysis product catalyses the reaction. Hence catalysis of a reaction by one of its products is called autocatalysis.

The catalyst is the substance which increases the rate of reaction by lowering the activation energy which alters the mechanism of the reaction.

Catalysis is the increase in the rate of a chemical reaction due to the participation of an additional substance called a catalyst which is not consumed in the catalysed reaction and can continue to act repeatedly.It increase rate of forward as well as backward reaction.

$K={Ae}^{\dfrac{-Ea}{RT}}$ 

A reaction inhibitor is a substance that decreases the rate of, or prevents, a chemical reaction. A catalyst, in contrast, is a substance that increases the rate of a chemical reaction.

• Promoters are substances that enhance the activity of a catalyst while poisons decrease the activity of a catalyst.
  
• In the manufacturing of sulfuric acid, a step involves the reaction of $SO _2$ and $O _2$ in presence of platinized asbestos to give $SO _3$

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:
$4C _3 H _5 (ONO _2) _3 \rightarrow 12CO _2 + 10H _2O + 6N _2 +O _2$

• 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 $\Delta H$.

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 it has large surface area.
Higher is the surface area, higher is the catalytic efficiency and vice versa.

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