Multiple Choice QuestionsIn which of the following molecules are all the bonds not equal?
ClF3
BF3
AlF3
AlF3
A.
ClF3
In ClF3 all bonds are not equal due to trigonal -bipyramidal (sp3d-hybridisation) geometry of ClF3 molecule.
BF3 and AlF3 show trigonal symmetric structure due to sp2-hybridisation.
NF3 shows pyramidal geometry due to sp3 hybridization.
Assume each reaction is carried out in an open container. For which reaction will ΔH = ΔE?
H2 (g) + Br2 (g) →2HBr (g)
C (s) + 2 H2O (g) → 2 H2 (g) + CO2 (g)
PCl5 (g) →PCl3 (g) + Cl2 (g)
PCl5 (g) →PCl3 (g) + Cl2 (g)
A.
H2 (g) + Br2 (g) →2HBr (g)
As we know that
ΔH = ΔE + PΔV
ΔH = ΔE +ΔnRT ..(1)
where ΔH → change in enthalpy of the system (standard heat at constant pressure)
Δ E → change in internal energy of system (Standard heat at constant volume)
Δn → no. of gaseous moles of product - no. of gaseous moles of reactant
R → gas constant
T → absolute temperature
If Δ n = 0 for reactions which is carried out in an open container, therefore, Δn = 0 for reactions which are carried out in an open container, therefore, ΔH =ΔE
so for reaction (1) Δn = 2-2 = 0
Hence, for reaction (1) , ΔH =ΔE
The enthalpy and entropy change for the reaction:
Br2 (l) + Cl2 (g)→ 2BrCl (g)
are 30 kJ mol-1 and 105 JK-1 mol-1 respectively. The temperature at which the reaction will be in equilibrium is:
285.7 K
273 K
450 K
450 K
A.
285.7 K
At equilibrium, Gibbs free energy change (ΔGo) is equal to zero. The following thermodynamic relation is used to show the relation of ΔGo with the enthalpy change (ΔHo) and entropy change (ΔSo)
ΔGo = ΔHo - ΔSo
0 = 30 x 103 (J mol-1) - T x 105 (J K-1) mol-1
Given: The mass of electron is 9.11 x 10-31 kg
Planck constant is 6.626 x 10-34 Js,
the uncertainty involved in the measurement of velocity within a distance of 0.1 A is:
5.79 x 106 ms-1
5.79 x 107 ms-1
5.79 x 108 ms-1
5.79 x 108 ms-1
A.
5.79 x 106 ms-1
By Heisenberg's uncertainty principle
The hydrogen ion concentration of a 10-8 M HCL aqueous solution at 298 K (Kw = 10-14) is:
1.0 x 10-6
1.0525 x 10-7 M
9.525 x 10-8 M
9.525 x 10-8 M
B.
1.0525 x 10-7 M
In aqueous solution of 10-8 M HCl, [H+] is based upon the concentration of H+ ion of 10-8 M HCl and concentration of H+ ion of water Kw of H2O = 10-14 = [H+][OH-] or [H+] = 10-7 M (due to neutral behaviour) os, in aqueous solution of 10-8 M HCl,
[H+] = [H+] of HCl +[H+] of water
= 10-8 + 10-7 = 11 x 10-8 M
1.10 x 10-7 M
The enthalpy of combustion of H2, cyclohexene (C6H10) and cyclohexene (C6H12) are -241, -3800 and -3920 kJ per mol respectively.The heat of hydrogenation of cyclohexane is:
-212 kJ mol
+121 kJ mol
+242 kJ per mol
+242 kJ per mol
A.
-212 kJ mol
ΔH= [ΔH of combustion of cyclohexane -(ΔH of combustion of cyclohexene +ΔH of combustion of H2)]
= -[-3920 -(3800-24)] kJ
= - [3920 + 4041] kJ
=-[121] kJ
=--121 kJ
Which of the following pairs consitutes a buffer?
HNO2 and NaNO2
NaOH and NaCl
HNO3 and NH4NO3
HNO3 and NH4NO3
A.
HNO2 and NaNO2
A pair constituent with an HNO2 and NaNO2 because HNO2 is weak acid and NaNO2 is a salt of the weak acid (HNO2) with a strong base (NaOH). Hence, it is an example of acidic buffer solution.
For the reaction,
CH4 (g) + 2 O2 (g) ⇌ CO2 (g) + 2H2O (l),
ΔrH = - 170. 8 kJ mol-1
Which of the following statements is not true?
At equilibrium, the concentrations of CO2 (g) and H2O (l) are not equal
The equilibrium constant for the reaction is given by Kp = 
Addition of CH4 (g) or O2 (g) at equilibrium will cause a shift to the right
Addition of CH4 (g) or O2 (g) at equilibrium will cause a shift to the right
B.
The equilibrium constant for the reaction is given by Kp =
For the reaction,
CH4 (g) + 2 O2 (g) ⇌ CO2 (g) + 2H2O (l),
ΔrH = - 170. 8 kJ mol-1
This equilibrium is an example of heterogeneous chemical equilibrium.Hence, for it
not correct expression.
In addition of CH4 (g) or O2 (g) at equilibrium Kc = will be decreased according to expression (i) but Kc remains constant at constant at constant temperature fro a reaction, so for maintaining the constant value of Kc, the concentration of CO2 will increase in same order. Hence, on the addition of CH4 or O2 equilibrium will cause to the right.
This reaction is an example of an exothermic reaction.
Identify the correct statement for the change of Gibbs energy for a system (ΔGsystem) at constant temperature and pressure
If ΔGsystem > 0, the process is spontaneous
If ΔGsystem =0, the system has attained equilibrium
If ΔGsystem < 0, the system is still moving in a particular direction
If ΔGsystem < 0, the system is still moving in a particular direction
B.
If ΔGsystem =0, the system has attained equilibrium
If the Gibbs free energy for a system (ΔGsystem) is equal to zero, then system is present in equilibrium at a constant temperature and pressure.
The orientation of an atomic orbital is governed by:
azimuthal quantum number
spin quantum number
magnetic quantum number
magnetic quantum number
C.
magnetic quantum number
The orientation of an atomic orbital is governed by magnetic quantum number.
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