CBSE Class 11 Chemistry Equilibrium Notes Set D

 EQUILIBRIUM

♦Equilibrium state- When rate of formation of a product in a process is in competition with rate of formation of reactants, the state is then named as “Equilibrium state” .

♦Equilibrium in physical processes: solid ⇌ liquid ⇌ gas H₂O(s )⇌ H₂O(l) ⇌ H₂O(_vap)

♦Law of chemical equilibrium: At a given temperature, the product ofconcentrations of the reaction productsraised to the respective stoichiometriccoefficient in the balanced chemicalequation divided by the product ofconcentrations of the reactants raised totheir individual stoichiometric coefficientshas a constant value. This is known asthe Equilibrium Law or Law of ChemicalEquilibrium. 

♦ If Qc >Kc, the reaction will proceed in thedirection of reactants (reverse reaction).If Qc <Kc, the reaction will proceed in thedirection of the products (forward reaction)

♦ Kp is equilibrium constant in terms of partial pressure of gaseous reactants and products.

♦ Kc is equilibrium constant in terms of molar concentration of gaseous reactants and products.

♦ Kp =Kc (RT)Δn here R is gas constant, T is temperature at which the process is carried out &Δn is no. of moles of gaseous product minus no. of moles of gaseous reactants.

♦ If Kc> 10³; Kc is very high i.e. the reaction proceeds nearly to completion.

♦ If Kc<10^3; Kc is very small i.e. the reaction proceeds rarely.

♦ If Kcis ranging in the range of 10³ to 10^-3; i.e. reactants and products are just in equilibrium.

♦ ΔG⁰ = – RT lnK or ΔG⁰ = – 2.303RT log K

♦ Factors affecting equilibrium constant:- temperature, pressure, catalyst and molar concentration of reactants and products. 

♦ Le Chatelier’s principle:- It states that a change in any of the factors thatdetermine the equilibrium conditions of asystem will cause the system to changein such a manner so as to reduce or tocounteract the effect of the change. 

♦ Arrhenius acids are the substances that ionize in water to form H+.

♦ Arrhenius bases are the substances that ionize in water to form OH-.

♦ Lewis acids are lone pair (of e-) accepters while Lewis bases are lone pair donators.

♦Proton donor are acids while proton accepters are bases(Bronsted-Lowry concept).

♦ The acid-base pair thatdiffers only by one proton is called a conjugateacid-base pair. IfBrönsted acid is a strong acid then itsconjugate base is a weak base and viceversa.

♦ Ionic product of water.Kw = [H+][OH–]

♦ pH = -log [H⁺] ; here[H+] is molar concentration of hydrogen ion.

♦ pH + pOH =14

♦pKa + pKb =14

♦ Ka x Kb = Kw = ionic product of water=1 x 10^-14 

♦ Buffer solution :The solutions which resist change in pH on dilution or with the addition of small amounts of acid or alkali are called Buffer Solutions.

♦ common ion effect: It can be defined as a shift in equilibrium on adding a substance that provides more of an ionic species already present in the dissociation equilibrium.

♦ Hydrolysis of Salts: process of interaction between water andcations/anions or both of salts is calledhydrolysis.

♦ The cations (e.g., Na⁺, K⁺,Ca²⁺, Ba²⁺, etc.) of strong bases and anions(e.g., Cl^–, Br^–, NO^3–, ClO^4– etc.) of strong acids simply get hydrated but do not hydrolyse, andtherefore the solutions of salts formed fromstrong acids and bases are neutral i.e., theirpH is 7.

♦ Salts of weak acid and strong base e.g.,CH₃COONa are basic in nature.

♦ Salts of strong acid and weak base e.g.,NH₄Cl, are acidic

♦Salts of weak acid and weak base, e.g.,CH₃COONH₄. The pH is determined by the formula pH = 7 + ½ (pKa – pKb)

♦ Solubility product- product of the molar concentrations of the ions in a saturated solution, each concentration term raised to the power equal to the no. of ions produced. 

QUESTIONS

Q.1. Mention the factors that affect equilibrium constant.
Ans. Temperature, pressure, catalyst and molar concentration of reactants and products.

Q.2. Whatis ionic products of water?
Ans. Kw = [H+] [OH-]

Q.3. Write conjugate acids of H₂O & NH₃.
Ans. H₃O+& NH₄+.

Q.4. Define Arrhenius acids.
Ans. Arrhenius acids are the substances that ionize in water to form H+.

Q.5. Define the term degree of ionization.
Ans.Extent up to which an acid/base/salt ionize to form ions.

Q.6. What are Buffer solutions?
Ans.The solutions which resist change in pH on dilution or with the addition of small amounts of acid or alkali are called Buffer Solutions.

Q.7. Write Kc for the gaseous reaction- N₂ + 3H₂⇌ 2NH₃
Ans. Kc=[NH₃]₂/[N₂] [H₂]₃

Q.8. Out of H₂O & H₃O+ which is stronger acid?
Ans. H₃O+.

Q.9. What is common ion effect?
Ans. Shift in equilibrium on adding a substance that provides more of an ionic species already present in the dissociation equilibrium.

Q.10. Write relationship between Kp and Kc for the gaseous reaction - N₂ + O₂ ⇌ 2NO
Ans.Kp = Kc asΔn is zero for the above said reaction.

 QUESTIONS
1. What is effect of catalyst on equilibrium constant „Kc‟?
Ans . A catalyst does not affect equilibrium constant because it speeds up both forward and backward reactions to the same extent.

2. State Le Chatelier‟r principle.
Ans.It states that a change in any of the factors thatdetermine the equilibrium conditions of asystem will cause the system to changein such a manner so as to reduce or tocounteract the effect of the change.

3. What is meant by conjugate acid –base pairs? Explain.
Ans:- H₂O + HCl⇌H₃O+ + Cl- base acid conjugate acid conjugate base

4. Classify the following bases as strong and weak bases: NaHCO3, NaOH, KOH, Ca(OH)2, Mg(OH)2.
Ans:-strong base NaOH, KOH ; weak bases NaHCO₃,Ca(OH)₂, Mg(OH)₂.

5. The concentration of hydrogen ion in a sample of soft drink is 3.8 × 10–3M. What is its pH ?
Ans:-pH = – log[3.8 × 10–3] = – {log[3.8] + log[10–3]} = – {(0.58) + (– 3.0)} = – { – 2.42} = 2.42 Therefore, the pH of the soft drink is 2.42and it is acidic.

6. The species: H2O, HCO3–, HSO4– and NH3can act both as Bronsted acids and bases.For each case give the correspondingconjugate acid and conjugate base.
Ans:-

7. Explain Lewis acids and bases with suitable examples.
Ans:-Lewis acids are lone pair (of e-) accepters while Lewis bases are lone pair donators. AlCl₃ is a Lewis acid while NH₃ is a Lewis base.

8. What is difference between alkali and bases? Give examples.
Ans:- An alkali is a water soluble base. All the alkalis are bases but all the bases are not alkali. Ex- NaOH is an alkali/base. Ca(OH)₂ is a base but not an alkali.

9. Explain homogeneous and heterogeneous equilibrium giving examples.
Ans:- If all the reactants and products present in an equilibrium mixture are in same phase→homogeneous equilibrium. If all the reactants and products present in an equilibrium mixture are in different phase→ heterogeneous equilibrium. N₂ (g) + 3H₂(g) ⇌2NH₃(g) homogeneous equilibrium CaCO₃(s)⇌CaO(s) + CO₂(g)heterogeneous equilibrium

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