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Chemical Reaction Engineering [ Question No: 1 To 20 ] :
The progressive conversion model is appropriate when
Assertion (A): Different assumptions about the rate determining step give different rate expressions for the same mechanism.
Reason (R): Each assumption puts a different combination of adsorption terms into the denominator.
State whether the following is true or false.
A bimodal pore structure with wide transport pores and fine reaction pores is a common design.
State whether the following is true or false.
Catalyst deactivation is usually allowed for by raising the temperature over the run.
Assertion (A): Catalyst pellets are made in shapes such as rings and trilobes rather than simple spheres.
Reason (R): Such shapes give a short diffusion path without the pressure drop of a small sphere.
A fluidised bed reactor is preferred over a fixed bed when
Assertion (A): Regeneration of a coked catalyst uses dilute rather than pure oxygen.
Reason (R): Burning the coke releases enough heat to sinter the catalyst if it is not controlled.
Assertion (A): A catalyst cannot shift the position of a chemical equilibrium.
Reason (R): It lowers the barrier in both the forward and the reverse direction equally.
The mean residence time obtained from an E curve is
The residence time distribution of a reactor describes
Arrange the steps of designing a non-isothermal reactor in order.
1. check for multiple steady states and runaway
2. obtain the kinetics and the heat of reaction
3. specify the heat transfer arrangement
4. write the coupled mole and energy balances
Assertion (A): An endothermic reactor is usually limited by heat supply rather than by kinetics.
Reason (R): The reaction cools itself, so the temperature falls unless heat is supplied at the rate the reaction consumes it.
Assertion (A): An adiabatic reactor for an exothermic reversible reaction is built as several beds with cooling between them.
Reason (R): The optimum temperature falls as conversion rises, and cooling between beds approximates that profile.
Assertion (A): A plug flow reactor gives a higher yield of a wanted intermediate than a stirred tank.
Reason (R): Every element in plug flow spends the same time in the reactor while a stirred tank spreads the times widely.
Assertion (A): Instantaneous selectivity and overall selectivity are different quantities.
Reason (R): The instantaneous value varies through the reactor while the overall value is an average of it.
For an autocatalytic reaction the best arrangement of several reactors is usually
A recycle reactor behaves like a CSTR when
A continuous stirred tank reactor at steady state operates at
Assertion (A): An autocatalytic reaction shows a rate that first rises and then falls as conversion proceeds.
Reason (R): The product catalyses the reaction, so the rate depends on both reactant and product concentrations.
All of the following are ways of determining reaction order EXCEPT
Total number of questions : 20
Number of answered questions : 0
Number of unanswered questions : 20
Chemical Reaction Engineering [ Question No: 1 To 20 ] :
The progressive conversion model is appropriate when
Your Answer : (Not Answered)
Correct Answer : A
Reaction then proceeds everywhere at once and the particle keeps its size while its composition changes. The two models are the extremes of a range and real particles often lie between them. The particle keeps its size in this model.
Assertion (A): Different assumptions about the rate determining step give different rate expressions for the same mechanism.
Reason (R): Each assumption puts a different combination of adsorption terms into the denominator.
Your Answer : (Not Answered)
Correct Answer : D
Both are true and the reason gives the origin: fitting data to several candidate expressions and choosing the best is how the controlling step is usually inferred. Each gives a distinct denominator. Discriminating between them takes real evidence.
State whether the following is true or false.
A bimodal pore structure with wide transport pores and fine reaction pores is a common design.
Your Answer : (Not Answered)
Correct Answer : B
The wide pores carry the reactant into the pellet and the fine ones provide the surface area. It is a direct response to the conflict between area and transport. Wide pores carry, fine pores react. The two functions are separated by design.
State whether the following is true or false.
Catalyst deactivation is usually allowed for by raising the temperature over the run.
Your Answer : (Not Answered)
Correct Answer : A
The extra rate compensates for the lost activity and holds conversion steady, and the end of run temperature is what limits the cycle. Raising it too far accelerates sintering and coking further. End of run temperature limits the cycle.
Assertion (A): Catalyst pellets are made in shapes such as rings and trilobes rather than simple spheres.
Reason (R): Such shapes give a short diffusion path without the pressure drop of a small sphere.
Your Answer : (Not Answered)
Correct Answer : C
Both are true and the reason gives the design objective, and it is a good example of a geometric solution to a conflict between two physical requirements. Void fraction rises with the shaped forms. Geometry solves a conflict the chemistry cannot.
A fluidised bed reactor is preferred over a fixed bed when
Your Answer : (Not Answered)
Correct Answer : A
Correct answer: the catalyst must be circulated continuously
Fluidisation makes the bed behave as a liquid, so catalyst can be drawn off, regenerated and returned continuously - which is exactly what a fluid catalytic cracker needs, its catalyst coking within seconds. The bed also gives excellent heat transfer and a near-uniform temperature. What it gives up is plug flow and mechanical simplicity, and it grinds its own catalyst by attrition.
Assertion (A): Regeneration of a coked catalyst uses dilute rather than pure oxygen.
Reason (R): Burning the coke releases enough heat to sinter the catalyst if it is not controlled.
Your Answer : (Not Answered)
Correct Answer : D
Both are true and the reason gives the hazard: the operation trades one deactivation mechanism for a worse and irreversible one if the temperature is allowed to run. Control of the burn is essential. Dilution keeps the peak temperature down.
Assertion (A): A catalyst cannot shift the position of a chemical equilibrium.
Reason (R): It lowers the barrier in both the forward and the reverse direction equally.
Your Answer : (Not Answered)
Correct Answer : B
Both are true and the reason gives the argument: the ratio of the two rate constants is unchanged, and that ratio is exactly the equilibrium constant. Both directions are accelerated equally. Only the approach to equilibrium is hastened.
The mean residence time obtained from an E curve is
Your Answer : (Not Answered)
Correct Answer : B
The mean is the area weighted average of time, which for a skewed distribution differs from the peak. For a well behaved reactor it should equal the volume divided by the volumetric flow. A shortfall points to dead volume.
The residence time distribution of a reactor describes
Your Answer : (Not Answered)
Correct Answer : A
It is a property of the flow pattern alone and says nothing directly about the chemistry. Two reactors with the same distribution can still give different conversions if the kinetics are not linear. It is a property of the flow alone.
Arrange the steps of designing a non-isothermal reactor in order.
1. check for multiple steady states and runaway
2. obtain the kinetics and the heat of reaction
3. specify the heat transfer arrangement
4. write the coupled mole and energy balances
Your Answer : (Not Answered)
Correct Answer : B
The balances cannot be written without the kinetics and the heat of reaction, and the hazard assessment must precede any decision about cooling. Specifying the hardware is the last step. Hazard assessment comes before hardware.
Assertion (A): An endothermic reactor is usually limited by heat supply rather than by kinetics.
Reason (R): The reaction cools itself, so the temperature falls unless heat is supplied at the rate the reaction consumes it.
Your Answer : (Not Answered)
Correct Answer : D
Correct answer: Both A and R are true, and R is the correct explanation of A
Both are true and the reason gives the cause. Because the reaction consumes heat, the temperature and therefore the rate fall unless heat is supplied at least as fast as the reaction takes it. The design problem becomes one of heat transfer rather than of kinetics, which is why steam reforming and ethane cracking are done in fired tubes of small diameter - the geometry is chosen to get heat in.
Assertion (A): An adiabatic reactor for an exothermic reversible reaction is built as several beds with cooling between them.
Reason (R): The optimum temperature falls as conversion rises, and cooling between beds approximates that profile.
Your Answer : (Not Answered)
Correct Answer : A
Both are true and the reason gives the design, and sulphuric acid converters and ammonia synthesis reactors are both built on exactly this principle. The profile falls as conversion rises. Each bed runs adiabatically between coolers.
Assertion (A): A plug flow reactor gives a higher yield of a wanted intermediate than a stirred tank.
Reason (R): Every element in plug flow spends the same time in the reactor while a stirred tank spreads the times widely.
Your Answer : (Not Answered)
Correct Answer : A
Both are true and the reason gives the mechanism: some material in a stirred tank leaves almost at once and some stays far too long, and both extremes lose the intermediate. A narrow residence time distribution is what helps.
Assertion (A): Instantaneous selectivity and overall selectivity are different quantities.
Reason (R): The instantaneous value varies through the reactor while the overall value is an average of it.
Your Answer : (Not Answered)
Correct Answer : D
Correct answer: Both A and R are true, and R is the correct explanation of A
Both are true and the reason gives the relation between them. The instantaneous value is local and varies with the composition and temperature at each point; the overall value is what actually leaves the reactor, and it is the flow-weighted average of the instantaneous values along the path. Designing for selectivity means arranging the reactor so that the instantaneous value stays high everywhere.
For an autocatalytic reaction the best arrangement of several reactors is usually
Your Answer : (Not Answered)
Correct Answer : B
The stirred tank jumps the mixture past the slow start and the plug flow reactor finishes efficiently. This is the standard illustration of matching the reactor to the shape of the rate curve. The rate has an interior maximum here.
A recycle reactor behaves like a CSTR when
Your Answer : (Not Answered)
Correct Answer : B
A large recycle mixes the contents thoroughly and brings the whole reactor towards the exit composition. With no recycle at all it behaves as a plug flow reactor, so the ratio spans both ideals. It is a useful laboratory reactor for this reason.
A continuous stirred tank reactor at steady state operates at
Your Answer : (Not Answered)
Correct Answer : A
Perfect mixing means every point in the vessel is at the exit composition, so the reaction proceeds at the lowest rate in the whole conversion range. This single fact explains most of the differences from a plug flow reactor.
Assertion (A): An autocatalytic reaction shows a rate that first rises and then falls as conversion proceeds.
Reason (R): The product catalyses the reaction, so the rate depends on both reactant and product concentrations.
Your Answer : (Not Answered)
Correct Answer : D
Both are true and the reason gives the shape: at the start there is no catalyst and at the end there is no reactant, so a maximum lies somewhere between and it decides the best reactor arrangement. A recycle reactor often suits such kinetics.
All of the following are ways of determining reaction order EXCEPT
Your Answer : (Not Answered)
Correct Answer : B
Correct answer: measuring the heat of reaction calorimetrically
The heat of reaction is a thermodynamic quantity fixed by the initial and final states, so it says nothing about how the rate depends on concentration. The other three are genuine methods: comparing half lives at several starting concentrations, testing trial integrated rate laws for the one that linearises the data, and taking slopes of concentration against time to fit the differential form directly.
Marks
Total number of questions : 20
Number of answered questions : 0
Number of unanswered questions : 20