Practice Pakistan's most useful MCQs for competitive exams

Cp – Cv for an ideal gas is equal to________________?

• (A)  R
• (B)  R/2
• (C)  2R
• (D)  3R

Answer

Submitted By :Ali Uppal

The vapor pressure of the solvent decreased by 10 mm Hg, when a non-volatile solute was added to the solvent. The mole fraction of the solute in the solution is 0.2. What should be the mole fraction of the solvent, if the decrease in vapor pressure of the solvent is required to be 20 mm Hg ?

• (A)  0.2
• (B)  0.1
• (C)  0.4
• (D)  0.6

Answer

Submitted By :Ali Uppal

One mole of methane undergoes complete combustion in a stoichiometric amount of air. The reaction proceeds as CH4 + 2O2 → CO2 + 2H2O. Both the reactants and products are in gas phase. ΔH°298 = – 730 kJ/mole of methane. Mole fraction of water vapour in the product gases is about_____________________?

• (A)  0.19
• (B)  0.33
• (C)  0.40
• (D)  0.67

Answer

Submitted By :Ali Uppal

At higher temperature, molal heat capacities of most of the gases (at constant pressure) ____________ with increase in temperature?

• (A)  Increases
• (B)  Decreases
• (C)  Remains unchanged
• (D)  Increases linearly

Answer

Submitted By :Ali Uppal

For water evaporating into unsaturated air under adiabatic conditions and at constant pressure, the ____________ remains constant throughout the period of vaporisation ?

• (A)  Dry bulb temperature
• (B)  Wet bulb temperature
• (C)  Humidity
• (D)  Relative saturation

Answer

Submitted By :Ali Uppal

The weight fraction of methanol in an aqueous solution is 0.64. The mole fraction of methanol XM satisfies________________?

• (A)  XM < 0.5
• (B)  XM = 0.5
• (C)  0.5 < XM < 0.64
• (D)  XM ≥ 0.64

Answer

Submitted By :Ali Uppal

Which of the following expressions defines the Baume gravity scale for liquids heavier than water ?

• (A)  (141.5/G) – 131.5
• (B)  145 – (145/G)
• (C)  200 (G-1)
• (D)  (400/G) – 400

Answer

Submitted By :Ali Uppal

A bypass stream in a chemical process is useful, because it___________________?

• (A)  Facilitates better control of the process
• (B)  Improves the conversion
• (C)  Increases the yield of products
• (D)  None of these

Answer

Submitted By :Ali Uppal

At standard conditions, N2 + 2O2 ⇌ 2NO2; ΔG° = 100 kJ/mole NO + ½O2 ⇌ 2NO2; ΔG° = -35 kJ/mole The standard free energy of formation of NO in kJ/mole is___________________?

• (A)  15
• (B)  30
• (C)  85
• (D)  170

Answer

Submitted By :Ali Uppal

Validity of the relationship, inputs = outputs, holds good for the system at steady state________________?

• (A)  With chemical reaction
• (B)  Without chemical reaction
• (C)  Without chemical reaction & losses
• (D)  None of these

Answer

Submitted By :Ali Uppal