Chemical Reaction MCQs

Free 472+ Chemical Reaction MCQs for PPSC, FPSC, NTS, and Pakistan government job tests. Practise below with answers and explanations.

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Chemical Reaction

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1.Identify the incorrect statement from the following:

In a first-order consecutive reaction, a tubular flow reactor offers lower overall selectivity compared to a stirred tank reactor.In an ideal continuous stirred tank reactor operating at steady state, the composition of the outlet stream matches that of the fluid inside the reactor.For any positive reaction order, a plug flow reactor (PFR) requires less volume than a mixed flow reactor to achieve the same conversion.During an autocatalytic reaction, the reaction rate remains nearly constant as the process continues.

2.Identify the incorrect statement from the following options:

For identical conversions, the residence time in a batch reactor is always the same as the space time in a plug flow reactor (PFR).Given two mixed reactors of different volumes used for producing a product via a second-order homogeneous reaction, placing the smaller reactor before the larger one in series maximizes the production rate.The Arrhenius equation, which relates the temperature to the rate constant, is expressed as: K = A·e^(-Ea/RT).The decomposition of CH3CHO into CH4 and CO in the presence of I2 proceeds through: CH3CHO + I2 → CH3I + HI + CO (slow step), followed by CH3I + HI → CH4 + I2 (fast step), where I2 acts as a catalyst.

3.Identify the accurate statement from the following options:

A reaction that absorbs heat is known as an exothermic reaction.A reaction that releases heat is termed an endothermic reaction.For a first-order reaction, the rate constant remains unaffected by changes in the concentration units.The state of chemical equilibrium is static and unchanging.

4.Which of the following statements is true?

A catalyst accelerates the forward reaction but decelerates the reverse reaction.Introducing a catalyst alters the value of the equilibrium constant.Variations in pressure do not affect the concentrations at equilibrium.A catalyst modifies the equilibrium composition of the reaction mixture.

5.Identify the accurate statement from the following:

A catalyst does not alter the enthalpy change (ΔH) of a reaction.A catalyst modifies the position of chemical equilibrium.The law of mass action was proposed by Le Chatelier.Activation energy is the difference in energy between reactants and products.

6.Identify the incorrect statement from the following:

Microbial fermentation reactions serve as examples of autocatalytic processes.In an irreversible series reaction, the slowest step predominantly determines the overall reaction rate.For an irreversible unimolecular first-order reaction, the fractional conversion remains identical in both constant and variable volume systems at any given time.The hydrolysis of esters under acidic or alkaline conditions follows zero-order kinetics.

7.Identify the incorrect statement from the following:

Visible light supplies the activation energy required for photochemical processes.In complex reactions, the reaction order and molecularity are always identical.For a reaction of second order, the slope of the rate versus concentration graph equals the rate constant.The molecularity of a reaction is always a positive integer greater than zero.

8.Identify the incorrect statement about catalysts:

A catalyst does not change the equilibrium position of a reversible reaction.A catalyst starts a chemical reaction.A catalyst acts specifically in certain reactions.A catalyst remains chemically unchanged after the reaction.

9.Identify the incorrect statement from the following options:

In a first-order reaction where A transforms into products, the reaction slows down over time because the concentration of A diminishes and the rate depends on A's concentration.Transition state theory tackles the calculation of reaction rates by focusing on the concept of activated complexes.According to penetration theory, the mass transfer coefficient reduces if the duration an eddy is exposed to the solute is shortened.For the irreversible reaction A + B → 2C with rate k·C_A·C_B, the reaction is always elementary.

10.Identify the incorrect statement from the following:

'Hold back' refers to the portion of material remaining in the system beyond the average residence time.Non-ideal flow reactors are experimentally analyzed using the stimulus-response method.When investigating a chemical reaction, it is beneficial to observe reactants at the beginning phase.Kinetic studies of catalytic reactions cannot be conducted using a batch reactor.

11.Identify the incorrect statement regarding the space velocity in flow reactors.

Space velocity is measured in units of reciprocal time.A space velocity of 3 hr⁻¹ indicates that three reactor volumes of feed enter the reactor per hour under specified conditions.A space velocity of 3 hr⁻¹ signifies that one-third of the reactor volume of feed is introduced per hour at specified conditions.All of the above statements are correct.

12.Which of the following statements about catalysts is accurate?

During catalytic processes, the catalyst interacts directly with the reactants.A catalyst triggers the start of a chemical reaction.A catalyst decreases the activation energy required for the reactants.A catalyst is not recovered in its original chemical form after the reaction.

13.Identify the incorrect statement regarding enzyme-catalyzed reactions:

The catalytic efficiency of enzymes is influenced by factors such as temperature, pH, and chemical agents.The majority of enzyme-catalyzed reactions require two or more substrates.Enzymes function by raising the activation energy needed for the reaction to proceed.The equilibrium concentrations in enzyme-driven reactions can be determined using the thermodynamic properties of the reactants and products.

14.Identify the incorrect statement from the following:

The vessel dispersion number (D/UL) approaches zero for both plug flow and mixed flow reactors.Space time in a flow reactor represents its capacity and equals the residence time if the reaction mixture's density remains constant.For any positive reaction order, a mixed flow reactor is always smaller than a plug flow reactor for the same duty.In an ideal tubular flow reactor, mixing occurs only in the radial direction, with no mixing along the flow direction.

15.Identify the incorrect statement from the following options:

The exit age distribution function E and the internal age distribution function I are connected by the relation E = - (dI/dθ).Chemisorption analysis helps in measuring the catalyst’s surface area and its pore size distribution.Elevated temperatures promote reactions that have higher activation energies.A catalyst raises the energy barrier that reactants must overcome to convert into products.

16.Identify the incorrect statement from the following options:

Using various catalysts in a reversible catalytic reaction does not alter the equilibrium composition.Alumina acts as a promoter when added to the iron catalyst during ammonia synthesis.The activation energy of a reaction is determined from the intercept on the Arrhenius plot.The presence of inert substances influences the equilibrium conversion of the reaction.

17.Identify the incorrect statement from the following options:

Chemical reactions exhibit greater sensitivity to temperature changes at higher temperatures.An extremely large equilibrium constant, K (K >> 1), suggests the reaction is essentially irreversible.The point where the Arrhenius plot intercepts the axis is known as the 'activation energy'.Non-ideal flow patterns in reactors occur due to factors like recycling, channeling, or formation of stagnant zones.

18.Identify the accurate statement from the following options:

Reactions with lower activation energy are favored at reduced temperatures.The dispersion number in a reactor or vessel is given by the ratio uL/D.In a multi-step reaction, the fastest step determines the overall rate.The Brunauer-Emmett-Teller (BET) method measures the pore volume and porosity of catalysts.

19.Identify the incorrect statement from the following options:

A batch reactor, typically used for liquid phase reactions, experiences changes in temperature, pressure, and composition over time.In a semi-batch reactor, one reactant is added all at once initially, while the other is introduced continuously during the process.A continuous flow reactor can maintain uniform concentration throughout the vessel even when thoroughly mixed.In a continuous flow reactor, reactants enter and products exit the system continuously.

20.Identify the incorrect statement from the following options:

The integral approach to analyzing kinetic data is preferred when the data shows significant scatter.The differential technique for kinetic data analysis demands higher precision or larger data sets.A reaction is classified as zero order if its rate does not change with temperature.For the same feed composition, flow rate, conversion, and any positive reaction order, the volume ratio of a plug flow reactor to a mixed flow reactor is always less than one.