Equilibrium
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The ionisation constant of an acid, Ka , is the measure of strength of an acid. The Ka values of acetic acid, hypochlorous acid and formic acid are 1.74 × 10–5, 3.0 × 10–8 and 1.8 × 10–4 respectively. Which of the following orders of pH of 0.1 mol dm–3 solutions of these acids is correct?
(i) Acetic acid > hypochlorous acid > formic acid
(ii) Hypochlorous acid > acetic acid > formic acid
(iii) Formic acid > hypochlorous acid > acetic acid
(iv) Formic acid > acetic acid > hypochlorous acid
The ionisation constant of an acid, Ka , is the measure of strength of an acid. The Ka values of acetic acid, hypochlorous acid and formic acid are 1.74 × 10–5, 3.0 × 10–8 and 1.8 × 10–4 respectively. Which of the following orders of pH of 0.1 mol dm–3 solutions of these acids is correct?
(i) Acetic acid > hypochlorous acid > formic acid
(ii) Hypochlorous acid > acetic acid > formic acid
(iii) Formic acid > hypochlorous acid > acetic acid
(iv) Formic acid > acetic acid > hypochlorous acid
This is a Multiple Choice Questions as classified in NCERT Exemplar
Ans: option (iv)
Higher the value of Ka higher will be the acidic strength Ka value for formic acid is the highest and that will be of hypochlorous acid is the lowest.
Upvote 
The pH of neutral water at 25°C is 7.0. As the temperature increases, ionisation of water increases, however, the concentration of H+ ions and OH– ions are equal. What will be the pH of pure water at 60°C?
(i) Equal to 7.0
(ii) Greater than 7.0
(iii) Less than 7.0
(iv) Equal to zero
The pH of neutral water at 25°C is 7.0. As the temperature increases, ionisation of water increases, however, the concentration of H+ ions and OH– ions are equal. What will be the pH of pure water at 60°C?
(i) Equal to 7.0
(ii) Greater than 7.0
(iii) Less than 7.0
(iv) Equal to zero
This is a Multiple Choice Questions as classified in NCERT Exemplar
Ans: As Kw increases Ans: As Kw increases [H+] [OH-] 10-14
[H+]= [OH-]
[H+]= [OH-] [H+]2 = 110-14
[H+] 10-7
Upvote When hydrochloric acid is added to cobalt nitrate solution at room temperature, the following reaction takes place and the reaction mixture becomes blue. On cooling the mixture it becomes pink. On the basis of this information mark the correct answer.
[Co (H2O)6] 3+ (aq) + 4Cl– (aq) ⇌ [CoCl4]2– (aq) + 6H2O (l)
(pink) (blue)
(i) ∆H > 0 for the reaction
(ii) ∆H < 0 for the reaction
(iii) ∆H = 0 for the reaction
(iv) The sign of ∆H cannot be predicted on the basis of this information.
When hydrochloric acid is added to cobalt nitrate solution at room temperature, the following reaction takes place and the reaction mixture becomes blue. On cooling the mixture it becomes pink. On the basis of this information mark the correct answer.
[Co (H2O)6] 3+ (aq) + 4Cl– (aq) ⇌ [CoCl4]2– (aq) + 6H2O (l)
(pink) (blue)
(i) ∆H > 0 for the reaction
(ii) ∆H < 0 for the reaction
(iii) ∆H = 0 for the reaction
(iv) The sign of ∆H cannot be predicted on the basis of this information.
This is a Multiple Choice Questions as classified in NCERT Exemplar
Ans: option (i)
On cooling the mixture reaction moves towards backward direction it means it is an endothermic reaction i.e.,
Upvote Which of the following statements is incorrect?
(i) In equilibrium mixture of ice and water kept in perfectly insulated flask mass of ice and water does not change with time.
(ii) The intensity of red colour increases when oxalic acid is added to a solution containing iron
(III) nitrate and potassium thiocyanate.
(iii) On addition of catalyst the equilibrium constant value is not affected.
(iv) Equilibrium constant for a reaction with negative ?H value decreases as the temperature increases.
Which of the following statements is incorrect?
(i) In equilibrium mixture of ice and water kept in perfectly insulated flask mass of ice and water does not change with time.
(ii) The intensity of red colour increases when oxalic acid is added to a solution containing iron
(III) nitrate and potassium thiocyanate.
(iii) On addition of catalyst the equilibrium constant value is not affected.
(iv) Equilibrium constant for a reaction with negative ?H value decreases as the temperature increases.
This is a Multiple Choice Questions as classified in NCERT Exemplar
Ans: option (ii)
The intensity of red colour increases when oxalic acid is added to a solution containing iron (III) nitrate and potassium thiocyanate.
Iron (III) nitrate and potassium thiocyanate react to give deep red coloratio
Upvote PCl5, PCl3 and Cl2 are at equilibrium at 500K in a closed container and their concentrations are 0.8 × 10–3 mol L–1, 1.2 × 10–3 mol L–1 and 1.2 × 10–3 mol L–1 respectively. The value of Kc for the reaction PCl5 (g) ⇌PCl3 (g) + Cl2 (g) will be
(i) 1.8 × 103 mol L–1
(ii) 1.8 × 10–3
(iii) 1.8 × 10–3 L mol–1
(iv) 0.55 × 104
PCl5, PCl3 and Cl2 are at equilibrium at 500K in a closed container and their concentrations are 0.8 × 10–3 mol L–1, 1.2 × 10–3 mol L–1 and 1.2 × 10–3 mol L–1 respectively. The value of Kc for the reaction PCl5 (g) ⇌PCl3 (g) + Cl2 (g) will be
(i) 1.8 × 103 mol L–1
(ii) 1.8 × 10–3
(iii) 1.8 × 10–3 L mol–1
(iv) 0.55 × 104
This is a Multiple Choice Questions as classified in NCERT Exemplar
Ans: The given reaction is :-
PCl5(g)?PCl3(g)+Cl2(g)
KC=
=1.2×10−3 ×1.2×10−3 0.8×10−3
=1.8×10−3molL−1
Upvote Which of the following is not a general characteristic of equilibria involving physical processes?
(i) Equilibrium is possible only in a closed system at a given temperature.
(ii) All measurable properties of the system remain constant.
(iii) All the physical processes stop at equilibrium.
(iv) The opposing processes occur at the same rate and there is dynamic but stable condition.
Which of the following is not a general characteristic of equilibria involving physical processes?
(i) Equilibrium is possible only in a closed system at a given temperature.
(ii) All measurable properties of the system remain constant.
(iii) All the physical processes stop at equilibrium.
(iv) The opposing processes occur at the same rate and there is dynamic but stable condition.
This is a Multiple Choice Questions as classified in NCERT Exemplar
Ans: option (iii)
A physical equilibrium is having dynamic nature, both forward and reverse process occur at equal rates. Some kind of motion is always present. The individual molecules continuously move from one phase to another.
Upvote Which of the following is not a general characteristic of equilibria involving physical processes?
(i) Equilibrium is possible only in a closed system at a given temperature.
(ii) All measurable properties of the system remain constant.
(iii) All the physical processes stop at equilibrium.
(iv) The opposing processes occur at the same rate and there is dynamic but stable condition.
Which of the following is not a general characteristic of equilibria involving physical processes?
(i) Equilibrium is possible only in a closed system at a given temperature.
(ii) All measurable properties of the system remain constant.
(iii) All the physical processes stop at equilibrium.
(iv) The opposing processes occur at the same rate and there is dynamic but stable condition.
This is a Multiple Choice Questions as classified in NCERT Exemplar
Ans: option (iii)
A physical equilibrium is having dynamic nature, both forward and reverse process occur at equal rates. Some kind of motion is always present. The individual molecules continuously move from one phase to another.
Upvote For the reaction H2(g) + I2(g) ⇌ 2HI (g), the standard free energy is ∆Gᶱ > 0. The equilibrium constant (K ) would be __________.
(i) K = 0
(ii) K > 1
(iii) K = 1
(iv) K < 1
For the reaction H2(g) + I2(g) ⇌ 2HI (g), the standard free energy is ∆Gᶱ > 0. The equilibrium constant (K ) would be __________.
(i) K = 0
(ii) K > 1
(iii) K = 1
(iv) K < 1
This is a Multiple Choice Questions as classified in NCERT Exemplar
Ans: Option(iv)
The given chemical reaction is:
H2(g) + I2(g) ? 2HI (g)
By, thermodynamical equation of equilibrium,
?G?= -RTlnk>0
Now, R>0 & T>0
⇒ −lnK > 0
⇒ K<1
Upvote We know that the relationship between Kc and Kp is
Kp = Kc (RT)∆n What would be the value of ∆n for the reaction
NH4Cl (s) ⇌ NH3 (g) + HCl (g)
(i) 1
(ii) 5
(iii) 5
(iv) 2
We know that the relationship between Kc and Kp is
Kp = Kc (RT)∆n What would be the value of ∆n for the reaction
NH4Cl (s) ⇌ NH3 (g) + HCl (g)
(i) 1
(ii) 5
(iii) 5
(iv) 2
This is a Multiple Choice Questions as classified in NCERT Exemplar
Ans: Option(iv)
The relationship between Kp and Kc is
Kp=Kc(RT)Δn
Where ?n = (number of moles of gaseous products) – (number of moles of gaseous reactants)
For the reaction,
NH4C1(s)?NH3(g)+HCl(g)
Δn=2–0=2
Upvote Following data is given for the reaction: CaCO3 (s) → CaO (s) + CO2 (g)
∆fHᶱ [CaO(s)] = – 635.1 kJ mol–1
∆fHᶱ[CO2(g)] = – 393.5 kJ mol–1
∆fHᶱ[CaCO3(s)] = – 1206.9 kJ mol–1
Predict the effect of temperature on the equilibrium constant of the above reaction.
Following data is given for the reaction: CaCO3 (s) → CaO (s) + CO2 (g)
∆fHᶱ [CaO(s)] = – 635.1 kJ mol–1
∆fHᶱ[CO2(g)] = – 393.5 kJ mol–1
∆fHᶱ[CaCO3(s)] = – 1206.9 kJ mol–1
Predict the effect of temperature on the equilibrium constant of the above reaction.
This is a Short Answer Type Questions as classified in NCERT Exemplar
Ans: ΔrH?= ?fH? [CaO(s)]+ ?fH?[CO2(g)]− ?fH?[ [CaCO3(s)]
∴ ?fH? =178.3kJ mol−1.
The reaction is endothermic. Hence, according to Le Chatelier’s principle, reaction will proceed in forward direction on increasing temperatur
Upvote