Instruction
- Total number of questions : 20
- Time allotted : 30:00 Minutes:Seconds.
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Chemical Process Calculations [ Question No: 1 To 20 ] :
Batch heating of a stirred tank by a coil gives a temperature that
All of the following are unsteady state situations EXCEPT
Match each situation with the form of its unsteady balance.
List I
A. Tank filling with no outlet
B. Well-mixed washout
C. Batch reactor
D. Semi-batch reactor
List II
1. accumulation equals the generation term
2. accumulation equals the inlet flow
3. accumulation equals inlet plus generation
4. accumulation equals minus the outlet term
A tank is filled at 10 litres per minute and drained at 4 litres per minute. At what rate does its contents accumulate?
State whether the following is true or false.
The humidity of saturated air depends only on temperature at a fixed total pressure.
Moist air holds water at a partial pressure of 1.7 kilopascals. If the saturation pressure equals 1.7 kilopascals at 15 degrees Celsius, what is the dew point?
From an Orsat analysis alone, the excess air is found by
Match each term with what it describes.
List I
A. Theoretical air
B. Excess air
C. Orsat analysis
D. Net calorific value
List II
1. a dry basis flue gas composition
2. the stoichiometric requirement
3. the heating value with water as vapour
4. the amount supplied above that requirement
Arrange the steps of a hypothetical path from a cold liquid to a superheated vapour in order.
1. heat the vapour to the final temperature
2. heat the liquid to its boiling point
3. sum the three enthalpy changes
4. vaporise it at the boiling point
Match each rule or method with what it estimates.
List I
A. Kopp's rule
B. Trouton's rule
C. Kirchhoff's relation
D. Watson correlation
List II
1. the heat of reaction at another temperature
2. the heat capacity of a solid from its elements
3. the latent heat at another temperature
4. the entropy of vaporisation at the normal boiling point
Assertion (A): A mean heat capacity may be used in place of an integral.
Reason (R): The mean value is defined so that multiplying it by the temperature change reproduces the integral exactly.
Three of the following contribute to the enthalpy change of a process stream. Which is the odd one out?
A reaction releases 500 kilojoules per mole and proceeds to an extent of 3 moles. How much heat must be removed to keep the reactor isothermal?
Arrange the steps of an energy balance calculation in the usual order.
1. construct a hypothetical path for each stream
2. complete the material balance first
3. sum the enthalpy changes and solve
4. choose a reference state for each species
A recycle loop receives 5 moles per hour of inert in the fresh feed. At steady state, how much inert must leave in the purge?
State whether the following is true or false.
The extent of reaction has a different value for each species in a reaction.
In a liquid-liquid extraction with immiscible solvents, the two carrier liquids
Parts per million by mass means
Arrange the steps of converting a mass per cent analysis to mole per cent.
1. total the moles obtained
2. take one hundred kilograms as the basis
3. divide each component by that total
4. divide each component mass by its molar mass
Molality is preferred to molarity in work over a range of temperatures because
Total number of questions : 20
Number of answered questions : 0
Number of unanswered questions : 20
Chemical Process Calculations [ Question No: 1 To 20 ] :
Batch heating of a stirred tank by a coil gives a temperature that
Your Answer : (Not Answered)
Correct Answer : C
Correct answer: approaches the coil temperature
The driving force for heat transfer is the difference between the coil and the contents, so as the contents warm the difference shrinks and the heating slows. The approach is exponential, and the contents can never exceed the coil temperature - which is why a steam coil at a given pressure sets a ceiling on what the batch can reach, however long it is heated.
All of the following are unsteady state situations EXCEPT
Your Answer : (Not Answered)
Correct Answer : C
The column at design conditions has settled and nothing changes with time. The other three all have a non-zero accumulation term and require a differential treatment. Design conditions are by definition a steady state.
Match each situation with the form of its unsteady balance.
List I
A. Tank filling with no outlet
B. Well-mixed washout
C. Batch reactor
D. Semi-batch reactor
List II
1. accumulation equals the generation term
2. accumulation equals the inlet flow
3. accumulation equals inlet plus generation
4. accumulation equals minus the outlet term
Your Answer : (Not Answered)
Correct Answer : D
Each case keeps a different subset of the general balance, and identifying which terms survive is the whole of setting the problem up. The integration that follows is then a matter of technique. Identifying the surviving terms is the real work.
A tank is filled at 10 litres per minute and drained at 4 litres per minute. At what rate does its contents accumulate?
Your Answer : (Not Answered)
Correct Answer : D
Correct answer: 6 litres per minute
\[ \frac{\mathrm{d}V}{\mathrm{d}t} = \dot{V}_{in} - \dot{V}_{out} = 10 - 4 = 6\ \mathrm{L/min}. \] Accumulation is what is left over when the outflow is subtracted from the inflow, and a positive value means the tank is filling. Adding the two rates gives the 14 offered, which would describe two streams entering rather than one entering and one leaving.
State whether the following is true or false.
The humidity of saturated air depends only on temperature at a fixed total pressure.
Your Answer : (Not Answered)
Correct Answer : D
Saturation fixes the water partial pressure at the vapour pressure of water, which is a function of temperature alone. The total pressure then converts that into a mass ratio, which is why the chart is drawn for one pressure.
Moist air holds water at a partial pressure of 1.7 kilopascals. If the saturation pressure equals 1.7 kilopascals at 15 degrees Celsius, what is the dew point?
Your Answer : (Not Answered)
Correct Answer : A
The dew point is by definition the temperature whose saturation pressure equals the actual partial pressure. Reading the steam table backwards from the partial pressure is the whole calculation. No other property of the air is needed for it.
From an Orsat analysis alone, the excess air is found by
Your Answer : (Not Answered)
Correct Answer : D
Nitrogen fixes the total air that entered, and the free oxygen remaining is what was not needed, so the ratio of the two gives the excess directly. This is why a single dry gas analysis is enough to check how a furnace is being run.
Match each term with what it describes.
List I
A. Theoretical air
B. Excess air
C. Orsat analysis
D. Net calorific value
List II
1. a dry basis flue gas composition
2. the stoichiometric requirement
3. the heating value with water as vapour
4. the amount supplied above that requirement
Your Answer : (Not Answered)
Correct Answer : C
The four appear together in almost every combustion problem, and confusing any pair leads to an answer that is internally consistent but wrong. Each has a precise definition worth memorising. Each appears in almost every furnace problem.
Arrange the steps of a hypothetical path from a cold liquid to a superheated vapour in order.
1. heat the vapour to the final temperature
2. heat the liquid to its boiling point
3. sum the three enthalpy changes
4. vaporise it at the boiling point
Your Answer : (Not Answered)
Correct Answer : A
The path is chosen so that each step matches a kind of tabulated data. Any other path between the same end states gives the same total, since enthalpy is a state function. The real process need not follow this path at all.
Match each rule or method with what it estimates.
List I
A. Kopp's rule
B. Trouton's rule
C. Kirchhoff's relation
D. Watson correlation
List II
1. the heat of reaction at another temperature
2. the heat capacity of a solid from its elements
3. the latent heat at another temperature
4. the entropy of vaporisation at the normal boiling point
Your Answer : (Not Answered)
Correct Answer : B
Correct answer: A-2, B-4, C-1, D-3
Four estimating rules for four different quantities. Kopp’s rule adds atomic contributions to estimate the heat capacity of a solid. Trouton’s rule puts the entropy of vaporisation at the normal boiling point near 88 joules per mole kelvin for ordinary liquids. Kirchhoff’s relation corrects a heat of reaction from one temperature to another using the heat capacity difference. And the Watson correlation scales a latent heat to another temperature using the reduced temperature.
Assertion (A): A mean heat capacity may be used in place of an integral.
Reason (R): The mean value is defined so that multiplying it by the temperature change reproduces the integral exactly.
Your Answer : (Not Answered)
Correct Answer : D
Both are true and the reason gives the definition: the mean is not a simple average of the end values but the value that gives the correct area, and it is tabulated against a reference temperature. Reading the interval off the table matters as much as the value.
Three of the following contribute to the enthalpy change of a process stream. Which is the odd one out?
Your Answer : (Not Answered)
Correct Answer : C
Correct answer: a change in the flow rate alone
Enthalpy change per unit mass depends on what happens to the material - its temperature, its phase, its chemical identity. Changing the flow rate alters the total rate of energy carried but not the enthalpy change of the stream itself, so it belongs to the material balance rather than to this list.
A reaction releases 500 kilojoules per mole and proceeds to an extent of 3 moles. How much heat must be removed to keep the reactor isothermal?
Your Answer : (Not Answered)
Correct Answer : B
The heat released is the heat of reaction times the extent, that is fifteen hundred kilojoules, and all of it must be removed for the temperature to stay constant. In an adiabatic reactor the same energy would raise the product temperature instead.
Arrange the steps of an energy balance calculation in the usual order.
1. construct a hypothetical path for each stream
2. complete the material balance first
3. sum the enthalpy changes and solve
4. choose a reference state for each species
Your Answer : (Not Answered)
Correct Answer : C
Nothing can be done until the flows are known, and the reference must be fixed before any enthalpy is written down. The path is then a matter of picking steps for which data exist. Heat capacities and latent heats are what is usually tabulated.
A recycle loop receives 5 moles per hour of inert in the fresh feed. At steady state, how much inert must leave in the purge?
Your Answer : (Not Answered)
Correct Answer : C
At steady state nothing accumulates, so the inert leaving must equal the inert entering. This single observation usually determines the purge flow before any other balance is written. Nothing may accumulate anywhere at steady state.
State whether the following is true or false.
The extent of reaction has a different value for each species in a reaction.
Your Answer : (Not Answered)
Correct Answer : B
It is a single quantity for the whole reaction, and the differing changes in each species come from the differing coefficients. That is the whole reason it is useful as a single unknown. One reaction therefore introduces exactly one new variable.
In a liquid-liquid extraction with immiscible solvents, the two carrier liquids
Your Answer : (Not Answered)
Correct Answer : A
Correct answer: each tie their own phase together
With immiscible solvents each carrier stays entirely in its own phase, so its flow is the same entering and leaving. Each therefore serves as a tie component for its own stream, and the balances can be written on a solute-free basis - which reduces the problem to tracking the solute alone and is the standard simplification in extraction calculations.
Parts per million by mass means
Your Answer : (Not Answered)
Correct Answer : C
One milligram in one kilogram is one part in a million by mass, which is the working definition. For dilute aqueous solutions it is nearly the same as milligrams per litre, since the density is close to one kilogram per litre.
Arrange the steps of converting a mass per cent analysis to mole per cent.
1. total the moles obtained
2. take one hundred kilograms as the basis
3. divide each component by that total
4. divide each component mass by its molar mass
Your Answer : (Not Answered)
Correct Answer : B
Choosing the basis first turns the percentages into masses, and the division by molar mass converts each to moles. Renormalising at the end is what makes the figures percentages again. The same four steps run in reverse for the other direction.
Molality is preferred to molarity in work over a range of temperatures because
Your Answer : (Not Answered)
Correct Answer : C
Correct answer: the solvent mass does not change with temperature
Molarity has a volume in its denominator, and the solution expands as it warms, so a solution made up to 1 molar at 20 degrees is slightly less than 1 molar at 60. Molality is a ratio of two masses, both of which are temperature-independent, so the value is fixed once the solution is made. That is why colligative property work and any experiment over a temperature range uses molality.
Marks
Total number of questions : 20
Number of answered questions : 0
Number of unanswered questions : 20