Chemical Kinetics

The rate of the thermal reactions will be ____.

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The rate of the thermal reactions will be slower than photochemical reactions. This is because, in photochemical reactions, reactants are irradiated by light radiations. Hence, photochemical reactions will be generally faster than thermal reactions.

The rate of a reaction generally depends on the ____.

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The rate of a reaction generally depends on the structure of the reactants. If the structures are very simple, rate of the reaction will be faster. If the structure of the reactants is complex, then rate of the reaction is relatively slow.

The rate of a reaction is defined as ____in unit time.

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The rate of a reaction is defined as the change in concentration of reactant in unit time. The remaining options will not affect the rate of the reaction.

The rate of the reaction does not depend on the concentration of the reactants for ____reactions.

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The rate of the reaction does not depend on the concentration of the reactants for zero order reactions. For all other reactions, concentration of reactants is considered.

Van't Hoff proposed the ____of the rate of a chemical reaction.

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Van't Hoff proposed the temperature dependence of the rate of a chemical reaction. Temperature changes the rate of the reaction drastically when compared to pressure and catalyst.

Homogeneous gas phase reactions are relatively fast compared to homogeneous reactions in a liquid phase because ____.

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Homogeneous gas phase reactions are relatively fast compared to homogeneous reactions in a liquid phase. This is because collision frequency is higher in gas phase, according to Arrhenious equation. If collisions are more, new bond formations will be more, thereby reaction will be faster.

The dissociation of hydrogen iodide is a ____ reaction.

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In the dissociation of hydrogen iodide, molecularity is bimolecular. 2HI→ H2 + I2. Here, two molecules of HI are involved to produce hydrogen and iodine molecules.

On the basis of Arrhenius theory, collisions having ____will lead to product formation.

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On the basis of Arrhenius theory, collisions having threshold energy and proper orientation will lead to product formation.

In the Arrhenius equation of temperature dependence of rate of the reaction, frequency factor is also called as ____.

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In the Arrhenius equation ( k=Ae-Ea/RT) of temperature dependence of rate of the reaction, frequency factor is also called as Pre-exponential factor or frequency factor. It is known as the pre-exponential factor, since it comes just prior to the exponential factor.

Decomposition of gaseous ammonia on hot platinum surface is the example for ____reaction.

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Decomposition of gaseous ammonia on hot platinum surface is the example for zero order reaction. In this reaction, platinum metal acts as a catalyst. At high pressure, the metal surface gets saturated with gas molecules. So, a further change in reaction conditions is unable to alter the amount of ammonia on the surface of the catalyst, making the rate of the reaction independent of its concentration.

For first order reaction, t1/2 is calculated from the equation ____.

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For first order reaction, t1/2 is calculated from the equation t1/2= 0.693/ k. Here, 'k' is the rate constant of the reaction.

The one method that will not be used for the determination of rate of a reaction is ____.

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The one method that will not be used for the determination of rate of a reaction is Ostwald's viscometry. This is used for the determination of the molecular weight of the polymer samples. The other three methods mentioned are used to determine the rate of the reaction.

In the hydrolysis of ethylacetate, the order of the reaction with respect to water is ____.

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In the hydrolysis of ethylacetate, the order of the reaction with respect to water is zero order. Since water is in excess quantity, its concentration won't change throughout the reaction. Hence, with respect to water, reaction is zero order.

The t1/2 of a reaction is doubled as the initial concentration of the reactant is doubled. The order of the reaction is ____ .

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The t1/2 of a reaction is doubled as the initial concentration of the reactant is doubled. The order of the reaction is zero order. For zero order reactions, t1/2 is directly proportional to the initial concentration of the reaction.

The function of promoter in a catalytic reaction is to ____.

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The function of a promoter in a catalytic reaction is to enhance the activity of the catalyst. For e.g. in the Haber's process of manufacturing ammonia, iron is used as catalyst. To enhance its catalytic activity, molybdenum is used as promoter.

Which of the statements is true about hydrolysis of esters?

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Hydrolysis of esters is a bimolecular reaction but follows a first order kinetics. It is therefore called a pseudo first order reaction.

In pseudo first order reaction, one of the reactants is in ____ .

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In pseudo first order reaction, one of the reactants is in large excess. Here, one of the reactants will be in a concentration far in excess than is needed. So, it is not considered for rate expression.

In a chemical reaction, ____ will result in increase in the rate of the reaction.

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In a chemical reaction, decrease in activation energy will result in increase in the rate of the reaction. The minimum energy needed for the reactants to react and start the reaction is called activation energy. If activation energy is less, the reaction will start in less time and the progress of the reaction will be faster.

During the catalytic reaction, ____ is changed in most of the reactions.

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During catalytic reaction, physical state of the catalyst is changed in most of the reactions. For example, coarse particles of MnO2 catalyst used in the decomposition of potassium chlorate to prepare O2, becomes finely divided powder at the end of the reaction.

The unit of rate constant for pseudo first order reaction is ____.

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The unit of rate constant for pseudo first order reaction is s-1. Since it follows first order, the same unit for first order is followed.

For zero order reaction t1/2 is directly proportional to the ____ .

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For zero order reaction, t1/2 is directly proportional to the initial concentration of the reactant. According to the equation for zero order reaction, t1/2 = Ro/2k. t1/2 is directly proportional to the initial concentration of the reactant and inversely proportional to the rate constant.

Artificial radioactive decay reactions follow ____ kinetics.

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Artificial radioactive decay reactions follow first order kinetics.

Arrhenius provided ____ for the temperature dependence of rate of a chemical reaction.

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Arrhenius provided physical justification for the temperature dependence of rate of a chemical reaction. It was initially proposed by Van't Hoff. However, Van't Hoff did not give any theoretical background for his proposal. The physical justification provided by Arrhenius, explained the temperature dependence.

Decomposition of ammonium nitrate is ____ a reaction.

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In the decomposition of ammonium nitrate, molecularity is unimolecular. In this decomposition only one reactant, ammonium nitrate, is involved and hence it is called unimolecular.

The main criteria for a fast reaction is ____.

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The main criteria for a fast reaction are large surface area. Other possibilities are smaller particle size, high temperature and high pressure.

Molecularity is used to know the ____of the reaction.

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Molecularity is used to know the mechanism of the reaction. Since molecularity is determined from the rate determining step, it gives idea about the mechanism of the reaction.

Half-life period is constant or independent of initial concentration of reactants for ____ reactions.

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Half-life period is a constant for first order reactions. For first order reactions, half-life time is independent of initial concentration of the reaction species.

In a single step reaction molecularity ____ is not observed.

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In a single step reaction, molecularity greater than three is not observed as the probability of more than three molecules undergoing simultaneous collision is very rare. If more than three molecules are involved, the reaction becomes very complex.

Catalyst will not be included in the rate expression equation, because _____________________.

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Catalyst will not be included in the rate expression equation, because concentration of the catalyst is not altered throughout the reaction.

Integrated rate equation gives information about_____________.

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Integrated rate equation gives information about concentration at different times. Here, rate expression can be written for any time t and the concentration at that time t can be determined.

Class 12th Chemistry - 4 Chemical Kinetics MCQs
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Class 12th Chemistry - 4 Chemical Kinetics MCQs