Practice Pakistan's most useful MCQs for competitive exams

A second order liquid phase reaction, A → B, is carried out in a mixed flow reactor operated in semi batch mode (no exit stream). The reactant A at concentration CAF is fed to the reactor at a volumetric flow rate of F. The volume of the reacting mixture is V and the density of the liquid mixture is constant. The mass balance for A is_______________________?

• (A)  d(VCA)/dt = -F (CAF – CA) – kCA2V
• (B)  d(VCA)/dt = F (CAF – CA) – kCA2V
• (C)  d(VCA)/dt = -FCA – kCA2V
• (D)  d(VCA)/dt = FCAF – kCA2V

Answer

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For a first order isothermal chemical reaction in a porous catalyst, the effectiveness factor is 0.3. The effectiveness factor will increase if the____________________?

• (A)  Catalyst size is reduced or the catalyst diffusivity is reduced
• (B)  Catalyst size is reduced or the catalyst diffusivity is increased
• (C)  Catalyst size is increased or the catalyst diffusivity is reduced
• (D)  Catalyst size is increased or the catalyst diffusivity is increased

Answer

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Which of the following fixes the volume of a batch reactor for a particular conversion and production rate ?

• (A)  Operating conditions (e.g. pressure and temperature)
• (B)  Rate constant
• (C)  Density of mixture
• (D)  None of these

Answer

Submitted By :Ali Uppal

The rate expression for a heterogeneous catalytic reaction is given by, – rA = K.KA PA(1 + KA.PA + KR.PR), where K is surface reaction rate constant and KA and KR are absorption equilibrium constants of A and R respectively. If KR PR >> (1 + KA PA), the apparent activation energy EA is equal to (given E is the activation energy for the reaction and ΔHR and ΔHA are the activation energies of adsorption of R and A) ?

• (A)  E
• (B)  E + ΔHA
• (C)  E + ΔHA – ΔHR)
• (D)  ΔHA + ΔHR

Answer

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An irreversible aqueous phase reaction, A + B → P, is carried out in an adiabatic mixed flow reactor. A feed containing 4kmole/m3 of each A and B enters the reactor at 8m3 /hr. If the temperature of the exit stream is never to exceed 390 K, what is the maximum inlet feed temperature allowed? Data: Heat of reaction = – 50 kJ/mole Density of the reacting mixture = 1000kg/m3 Specific heat of reacting mixture = 2kJ/kg.K The above data can be assumed to be independent of temperature and composition?

• (A)  190
• (B)  290
• (C)  390
• (D)  490

Answer

Submitted By :Ali Uppal

A catalyst in a chemical reaction____________________?

• (A)  Decreases the activation energy
• (B)  Alters the reaction mechanism
• (C)  Increases the frequency of collisions of reacting species
• (D)  All

Answer

Submitted By :Ali Uppal

The following gas phase reaction is taking place in a plug flow reactor. A stoichiometric mixture of A and B at 300 K is fed to the reactor. At 1 m along the length of the reactor, the temperature is 360 K. The pressure drop is negligible and an ideal gas behaviour can be assumed. Identify the correct expression relating the concentration of A at the inlet (CA0), concentration of A at 1m (CA) and the corresponding conversion of A (X) ?

• (A)  CA = 1.2 CA0 (1 – X)/(1 – 0.33X)
• (B)  CA = 1.2 CA0 (1 – X)/(1 – 0.5X)
• (C)  CA = 0.83 CA0 (1 – X)/(1 – 0.33X)
• (D)  CA = 0.83 CA0 (1 – X)/(1 – 0.5X)

Answer

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Mean residence time is equal to the space time, when_________________?

• (A)  The feed rate is measured at temperature and pressure in the reactor
• (B)  The temperature, pressure and the density of reaction mixture remains constant throughout the reactor
• (C)  There is no change in number of moles in gaseous reaction
• (D)  All

Answer

Submitted By :Ali Uppal

In a chemical reaction, represented by as shown in the bellow figure, it is observed that the (i) Rate of reaction increases by a factor of 4 on doubling the concentration of the reactant. (ii) Rate of reaction increases by a factor of 9 on trebling the concentration of the reactant. Then the rate of the reaction is proportional to(where, CA = concentration of the reactant)_____________________?

• (A)  CA
• (B)  CA2
• (C)  CA3
• (D)  CA4

Answer

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Knudsen diffusion is directly proportional to _____________________?

• (A)  T
• (B)  √T
• (C)  1/√T
• (D)  T2

Answer

Submitted By :Ali Uppal