BCHCT-133 Solved Assignment January 2026 | CHEMICAL ENERGETICS, EQUILIBRIA AND FUNCTIONAL ORGANIC CHEMISTRY I | IGNOU BSCG

Q: Consider the following reaction N₂ + 3 H₂ ⇌ 2NH₃ In which direction, towards reactants and towards products, does the reaction shift if the equilibrium is stressed by each change?

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Q1. List the differences between thermodynamically reversible and irreversible processes with the suitable examples.

Key Points:

Reversible processes are ideal, proceed infinitesimally slowly, and remain in equilibrium with surroundings.
Irreversible processes are real, spontaneous, occur at a finite rate, and are not in equilibrium.
A reversible process can be reversed by infinitesimal changes, leaving no net change in the universe.
An irreversible process cannot be reversed without leaving permanent changes in the surroundings.

Answer: Thermodynamically, processes are fundamentally categorised as reversible or irreversible, a crucial distinction in chemical energetics addressed in BCHCT-133. A **reversible process** is an idealised pathway where the system remains in infinitesimal equilibrium with its surroundings throughout. It proceeds infinitely slowly, meaning an infinitesimal change in conditions can reverse its direction, allowing both the system and surroundings to return to their exact initial states without any net pe...

Q2. Derive a relation between temperature and volume for an adiabatic process. 1.00 mole of helium gas at temperature of 100 °C undergoes reversible adiabatic expansion from an initial volume of 5 dm³ to 30 dm³. Calculate the final temperature of the gas by assuming that the helium behaves ideally and has Cv,m = 12.47 JK⁻¹mol⁻¹.

Key Points:

Adiabatic process implies no heat exchange with surroundings (dQ = 0).
First law for adiabatic: dU = dW, where dU = nCv,m dT and dW = -P dV.
Derivation for ideal gas yields T V^(γ-1) = constant, where γ = Cp,m / Cv,m.
For an ideal gas, Cp,m = Cv,m + R.

Answer: For a reversible adiabatic process involving an ideal gas, the system exchanges no heat with its surroundings (dQ = 0). According to the first law of thermodynamics, this means the change in internal energy (dU) is solely due to the work done (dW), so dU = dW. For an ideal gas, the change in internal energy is given by dU = nCv,m dT, where n is moles, Cv,m is molar heat capacity at constant volume, and dT is the change in temperature. For a reversible process, the work done is dW = -P dV. Subst...

Q3. Two molecule of ∝ -D -glucose condense in enzyme catalyzed reaction to give a molecule of disaccharide, maltose. Calculate the enthalpy of the reaction. The enthalpies of combustion of crystalline ∝ -D -glucose and maltose at 25 °C are -2809.1 kJmol⁻¹ and 5645.5 kJmol⁻¹, respectively.

Key Points:

The reaction involves two glucose molecules condensing to form one maltose and one water molecule.
Hess's Law is applied to calculate reaction enthalpy from combustion data.
The enthalpy of reaction (ΔH°_rxn) equals ΣΔH°_c(reactants) - ΣΔH°_c(products).
Enthalpy of combustion for α-D-glucose is -2809.1 kJmol⁻¹.

Answer: The condensation of two molecules of α-D-glucose to form maltose is represented by the following chemical equation: 2 C₆H₁₂O₆ (s, α-D-glucose) → C₁₂H₂₂O₁₁ (s, maltose) + H₂O (l) To calculate the enthalpy of this reaction (ΔH°_rxn) using enthalpies of combustion, we apply Hess's Law. This principle states that the total enthalpy change for a reaction is independent of the pathway taken. We can envision a pathway where reactants are combusted, and then products are formed from the combustion pro...

Q4. Differentiate between enthalpy driven and entropy driven reactions with the help of suitable examples. What is the chemical potential? Explain it with its significance.

(a)) Differentiate between enthalpy driven and entropy driven reactions with the help of suitable examples. (80 words)
(b)) What is the chemical potential? Explain it with its significance. (120 words)

Key Points:

Enthalpy-driven reactions: ΔH < 0, exothermic, release heat (e.g., combustion).
Entropy-driven reactions: ΔS > 0, increase disorder, spontaneous at high T (e.g., decomposition).
Gibbs Free Energy: ΔG = ΔH - TΔS determines spontaneity.
Chemical potential (μ): Partial molar Gibbs free energy.

Answer: Chemical reactions are driven by changes in thermodynamic properties, primarily enthalpy (ΔH) and entropy (ΔS). The overall spontaneity is determined by the Gibbs free energy change (ΔG = ΔH - TΔS). While some reactions release heat (exothermic, enthalpy-driven), others proceed due to an increase in disorder (entropy-driven). The concept of chemical potential further elucidates the driving force for matter transfer and chemical change, aiming towards equilibrium.

Q5. In the equilibrium mixture of three ideal gases A, B, C A (g) ⇌ B (g) + C (g) obtained by dissociation of A to the extent of 20 % at a total pressure of 1.0 atm, what are the partial pressure of A, B and C.

Key Points:

Extent of dissociation (α) quantifies the fraction of reactant that decomposes at equilibrium.
Equilibrium moles are calculated by subtracting dissociated amount from initial, and adding formed products.
Total moles at equilibrium are the sum of moles of all species present.
Mole fraction (Xᵢ) of a gas is its moles divided by total moles at equilibrium.

Answer: To determine the partial pressures of A, B, and C at equilibrium, we first need to calculate the equilibrium moles of each gas using the given extent of dissociation. The reaction is A (g) ⇌ B (g) + C (g). Let's assume we start with 1 mole of A. At equilibrium, A dissociates by 20%, which means 0.20 moles of A dissociate. According to the stoichiometry, this will produce 0.20 moles of B and 0.20 moles of C. The equilibrium moles are: Initial moles of A = 1.0 mol Change in A = -0.20 mol Equilib...

Q6. Consider the following reaction N₂ + 3 H₂ ⇌ 2NH₃ In which direction, towards reactants and towards products, does the reaction shift if the equilibrium is stressed by each change?

(i)) H₂ is added (67 words)
(ii)) NH₃ is added (67 words)
(iii)) NH₃ is removed. (66 words)

Key Points:

Le Chatelier's Principle: System adjusts to relieve applied stress.
Adding reactant: Equilibrium shifts to consume it, favoring products.
Adding product: Equilibrium shifts to consume it, favoring reactants.
Removing product: Equilibrium shifts to replenish it, favoring products.

Answer:

Q7. Which factor affect the degree of ionization of weak electrolyte. Explain in brief. Calculate the pH of 0.010 M aqueous solution of NaOH at 25 °C.

(a)) Which factor affect the degree of ionization of weak electrolyte. Explain in brief. (80 words)
(b)) Calculate the pH of 0.010 M aqueous solution of NaOH at 25 °C. (120 words)

Key Points:

Weak electrolyte ionization is influenced by concentration, temperature, and common ion effect.
Ostwald's Dilution Law states that dilution increases the degree of ionization for weak electrolytes.
Common ion effect suppresses the ionization of a weak electrolyte by shifting equilibrium.
NaOH is a strong base, completely dissociating to yield [OH⁻] equal to its initial concentration.

Answer: The degree of ionization of a weak electrolyte is influenced by several factors that shift the equilibrium between its un-ionized and ionized forms. For weak acids or bases, their partial dissociation in water creates an equilibrium, and any change that disrupts this equilibrium affects the extent of ionization. Understanding these factors is crucial for predicting and controlling the behavior of weak electrolytes in solution. For strong bases like NaOH, the calculation of pH is straightforward...

Q8. Explain the effect of common ion on the ionization equilibrium of weak acids with the help of a suitable example. The pH of an aqueous solution of lactic acid CH₃CH(OH)COOH-a weak acid was found to be 2.7. Calculate the concentration of solution if Kₐ for lactic acid is 1.4 × 10⁻⁴.

(a)) Explain the effect of common ion on the ionization equilibrium of weak acids with the help of a suitable example. (80 words)
(b)) The pH of an aqueous solution of lactic acid CH₃CH(OH)COOH-a weak acid was found to be 2.7. Calculate the concentration of solution if Kₐ for lactic acid is 1.4 × 10⁻⁴. (120 words)

Key Points:

Common ion effect: suppression of weak electrolyte ionization by a strong electrolyte with a shared ion.
Le Chatelier's principle dictates common ion effect: equilibrium shifts to relieve stress (added common ion).
Adding sodium acetate to acetic acid reduces [H⁺] and increases pH due to the common ion effect.
pH is derived from [H⁺] concentration using pH = -log[H⁺].

Answer: The provided question requires an explanation of the common ion effect on weak acid ionization and a calculation involving lactic acid's pH and Kₐ. Detailed answers for each sub-question are provided below, adhering to specific word limits and formatting guidelines.

Q9. Arrange the following salt of magnesium in the order of increasing solubilities. MgF₂, MgCO₃, Mg₃(PO₄)₂ [Given: Ksp(MgF₂) = 3.7 × 10⁻⁸; Ksp(MgF₂) = 3.5 × 10⁻⁸; and Ksp(MgF₂) = 1.0 × 10⁻²⁵ at 25 °C.]

Key Points:

Molar solubility (s) quantifies the maximum amount of a salt that dissolves in a solvent.
Ksp (solubility product constant) defines the equilibrium for sparingly soluble ionic compounds.
Direct comparison of Ksp values for solubility is only valid for salts with the same ion stoichiometry.
Molar solubility for MgF₂ (AB₂ type) is derived from Ksp = 4s³.

Answer: To arrange magnesium salts in increasing solubility, we must calculate the molar solubility (s) for each using its Ksp, as direct Ksp comparison is only valid for salts with identical stoichiometries. Acknowledging a potential typo in the question, we assume the given Ksp values correspond sequentially to MgF₂, MgCO₃, and Mg₃(PO₄)₂. Thus, we use Ksp(MgF₂) = 3.7 × 10⁻⁸, Ksp(MgCO₃) = 3.5 × 10⁻⁸, and Ksp(Mg₃(PO₄)₂) = 1.0 × 10⁻²⁵. For MgF₂ (which dissociates as Mg²⁺ + 2F⁻), the Ksp expression is Ks...

Q10. A 1.00 mol sample of NOCl was placed in a 2.00 L reactor and heated to 227 °C until the system reached equilibrium. The contents of the reactor were then analyzed and found to contain 0.056 mol of Cl₂. Calculate K at this temperature. The equation for the decomposition of NOCl to NO and Cl₂ is as follows: 2NOCl(g) → 2NO(g) + Cl₂(g)

Key Points:

Equilibrium constant (K_c) quantifies product-to-reactant ratio at equilibrium.
ICE (Initial, Change, Equilibrium) table method simplifies equilibrium calculations.
Initial concentrations are calculated from initial moles and reactor volume.
Equilibrium concentration of Cl₂ (0.028 M) is used to determine 'x' in the ICE table.

Answer: As per BCHCT-133 course material on chemical equilibrium, calculating the equilibrium constant (K_c) involves determining the equilibrium molar concentrations of all reactants and products. We begin by establishing the initial concentrations of the species in the reaction: 2NOCl(g) ⇌ 2NO(g) + Cl₂(g). The initial concentration of NOCl is 1.00 mol / 2.00 L = 0.500 M, while NO and Cl₂ are initially 0 M, as they are products yet to form. Next, we utilize an ICE (Initial, Change, Equilibrium) table ...

Q11. What is Hückel rule? Define this with suitable example. How would you prepare benzene from ethyne? Write its mechanism.

(a)) What is Hückel rule? Define this with suitable example. (80 words)
(b)) How would you prepare benzene from ethyne? Write its mechanism. (120 words)

Key Points:

Hückel's Rule specifies (4n + 2) π electrons for aromaticity in cyclic, planar, conjugated systems.
Benzene is aromatic with 6 π electrons (n=1), satisfying Hückel's rule.
Benzene is synthesized from ethyne via cyclic trimerization reaction.
The trimerization involves passing ethyne through a red hot iron tube at ~400°C.

Answer:

Q12. What are the limitations of Friedel-Crafts alkylation reactions? Write the product of the following reactions.

(a)) What are the limitations of Friedel-Crafts alkylation reactions? (80 words)
(i)) Write the product of the following reaction: [image] + H₂SO₄ + SO₃ (40 words)
(ii)) Write the product of the following reaction: [image] + Cl AlCl₃ (40 words)
(iii)) Write the product of the following reaction: [image] + 3H₂ Ni, 425-525 K 25 atm. (40 words)

Key Points:

Friedel-Crafts alkylation suffers from polyalkylation, leading to mixed products.
Carbocation rearrangements can yield unexpected alkylation isomers.
Deactivated aromatic rings and basic amines are incompatible with FC alkylation.
Benzene reacts with H₂SO₄/SO₃ to form benzenesulfonic acid (sulfonation).

Answer: The following response addresses the limitations of Friedel-Crafts alkylation and identifies the products for the given aromatic reactions, drawing upon principles of electrophilic aromatic substitution and reduction.

Q13. Write the mechanism of chlorination of methyl benzene. Predict the reactant of the following reaction.

(a)) Write the mechanism of chlorination of methyl benzene. (80 words)
(i)) Predict the reactant of the following reaction: KMnO₄, H₂O, Product: COOH [image] (40 words)
(ii)) Predict the reactant of the following reaction: KMnO₄, Δ, Br₂, FeBr₃, Product: COOH and Br (Minor) [image] (40 words)
(iii)) Predict the reactant of the following reaction: AlCl₃, Product: CH₃ [image] (40 words)

Key Points:

Chlorination of toluene via EAS uses a Lewis acid catalyst to form o/p-chlorotoluene.
EAS mechanism involves electrophile generation, arenium ion formation, and proton abstraction.
Aqueous KMnO₄ oxidizes alkyl side chains (with benzylic H) on benzene to carboxylic acids.
Methyl benzene (toluene) is oxidized to benzoic acid by strong oxidizers like KMnO₄.

Answer:

Q14. Arrange the following molecules in order of increasing boiling points. Give reason for this trend: CHCl₃, CH₂Cl₂, CH₃Cl, CCl₄. Complete the following reactions.

(a)) Arrange the following molecules in order of increasing boiling points. Give reason for this trend: CHCl₃, CH₂Cl₂, CH₃Cl, CCl₄ (80 words)
(i)) Complete the following reaction: [image structure] + SOCI₂ (40 words)
(ii)) Complete the following reaction: [image structure] + HBr Peroxide (40 words)
(iii)) Complete the following reaction: H₂C=CHCH₂CH₃ + Br₂ Heat (40 words)

Key Points:

Boiling points are directly related to the strength of intermolecular forces (IMFs).
London Dispersion Forces (LDFs) increase with molecular weight and electron count, dominating for larger molecules.
Polar molecules also possess dipole-dipole interactions, but LDFs often prevail in heavier molecules.
Alcohols (R-OH) react with thionyl chloride (SOCI₂) to form alkyl chlorides (R-Cl).

Answer:

Q15. Which of the following compounds undergo Sɴ1/Sɴ2 reaction? Explain. Write the product and mechanism of the following reaction.

(a)) Which of the following compounds undergo Sɴ1/Sɴ2 reaction? Explain. (i) Benzyl chloride; (ii) Chlorobenzene; (iii) Chloroethene; (iv) Chloroethyne (80 words)
(b)) Write the product and mechanism of the following reaction: [image reaction Br OCH3 NaNH2, liq. NH3] (120 words)

Key Points:

Benzyl halides undergo Sɴ1 due to resonance-stabilized carbocations and Sɴ2 as primary halides.
Aryl, vinylic, and acetylenic halides do not readily undergo Sɴ1/Sɴ2 due to C-X partial double bond character.
The reaction of aryl halides with strong bases (e.g., NaNH₂) proceeds via the benzyne mechanism.
The benzyne mechanism involves dehydrohalogenation to form a benzyne intermediate, followed by nucleophilic addition.

Answer: The reactivity of organic compounds towards Sɴ1/Sɴ2 reactions depends critically on the stability of the intermediate carbocation (for Sɴ1) and the steric/electronic environment of the reacting carbon (for Sɴ2). Aryl, vinylic, and acetylenic halides exhibit reduced reactivity due to resonance effects and hybridization, while benzylic halides are highly reactive. Nucleophilic aromatic substitution via the benzyne mechanism offers an alternative pathway for aryl halides under strong basic conditio...

Q16. Complete the following reaction and write its mechanism: [image reaction OH TsCl Pyridine A Nal Acetone B]

Key Points:

Tosylation converts a hydroxyl group (-OH) into an excellent tosylate leaving group (-OTs).
Tosyl chloride (TsCl) with pyridine is used for the tosylation of alcohols to form product A.
Product A (alkyl tosylate) undergoes an SN2 reaction with sodium iodide (NaI) to form alkyl iodide (B).
Acetone is a polar aprotic solvent, which promotes SN2 reactions by enhancing nucleophile reactivity.

Answer: The given reaction sequence transforms an alcohol (R-OH) into an alkyl iodide (R-I) through a two-step process, leveraging the principles of leaving group activation and nucleophilic substitution, as covered in BCHCT-133. **Step 1: Formation of A (Tosylation)** In the first step, the alcohol (R-OH) reacts with tosyl chloride (TsCl) in the presence of pyridine. Pyridine acts as a base to neutralize the hydrochloric acid formed during the reaction. This converts the poor leaving group, the hydrox...

Q17. Write the mechanism of the formation of salicylic acid from phenol.

Key Points:

Salicylic acid forms from phenol via the Kolbe-Schmitt reaction.
Phenol is first deprotonated to form the more nucleophilic phenoxide ion.
Carbon dioxide (CO₂) acts as the electrophile in this reaction.
Electrophilic attack by CO₂ occurs predominantly at the *ortho* position.

Answer: The formation of salicylic acid from phenol is achieved through the Kolbe-Schmitt reaction, a classic example of electrophilic aromatic substitution involving a phenoxide intermediate. This mechanism initiates by treating phenol with a strong base, typically sodium hydroxide (NaOH), to form sodium phenoxide. Deprotonation of the phenolic hydroxyl group yields the phenoxide ion, which is significantly more nucleophilic than phenol itself. This enhanced nucleophilicity is due to the negative char...

Q18. Give two important features of the crown ethers. Write product for the following reactions.

(a)) Give two important features of the crown ethers. (80 words)
(i)) Write product for the following reaction: [image reaction with CH3, HI] (40 words)
(ii)) Write product for the following reaction: [image reaction with CH3, i) PhMgBr ii) H3O+] (40 words)
(iii)) Write product for the following reaction: [image reaction with H3C Et CH3 H₂SO₄/EtOH] (40 words)

Key Points:

Crown ethers are cyclic polyethers that complex metal cations via host-guest chemistry.
They act as phase transfer catalysts, solubilizing ionic salts in organic solvents.
Ether cleavage with HI on isopropyl methyl ether yields isopropanol and iodomethane.
Grignard addition of PhMgBr to acetaldehyde, followed by hydrolysis, produces 1-phenylethanol.

Answer: Crown ethers are cyclic polyethers renowned for their ability to bind metal cations. Their unique structure allows them to facilitate reactions by solubilizing ionic species in non-polar environments. The subsequent reaction products demonstrate fundamental transformations in organic chemistry, including ether cleavage, Grignard additions, and acid-catalyzed etherification.

Q19. How will you prepare primary, secondary and tertiary alcohols from same Grignard reagent?

Key Points:

Primary alcohols are formed by reacting a Grignard reagent with formaldehyde (HCHO).
Secondary alcohols result from the reaction of a Grignard reagent with any aldehyde other than formaldehyde.
Tertiary alcohols are synthesized by reacting a Grignard reagent with a ketone.
Grignard reagents act as strong nucleophiles, adding to the electrophilic carbonyl carbon.

Answer: Grignard reagents (RMgX) are highly versatile organometallic compounds used to synthesize various classes of alcohols via nucleophilic addition to carbonyl compounds, as discussed in BCHCT-133 Unit 12. The specific type of alcohol (primary, secondary, or tertiary) formed from the *same* Grignard reagent depends entirely on the carbonyl compound it reacts with. To prepare a **primary alcohol**, the Grignard reagent is reacted with formaldehyde (HCHO). Formaldehyde is the simplest aldehyde, havin...

Q20. How will you bring about following conversions?

(a)) Benzaldehyde to cinnamaldehyde (40 words)
(b)) Benzaldehyde to cinnamic acid (40 words)
(c)) Acetophenone to dypnone (40 words)
(d)) Acetophenone to 1,2,3-triphenylbenzene (40 words)
(e)) Acetophenone to 1-Phenyl-1,3-butanedione (40 words)

Key Points:

Claisen-Schmidt reaction: Cross-aldol of benzaldehyde with acetaldehyde to form cinnamaldehyde.
Perkin reaction: Aromatic aldehyde + acid anhydride + salt yields α,β-unsaturated acid (e.g., cinnamic acid).
Aldol condensation: Base-catalyzed self-condensation of acetophenone produces dypnone.
β-Diketone synthesis: Acylation of ketone enolate (acetophenone) with ester/anhydride yields 1-phenyl-1,3-butanedione.

Answer:

BCHCT-133 Solved Assignment — January 2026 / July 2026

CHEMICAL ENERGETICS, EQUILIBRIA AND FUNCTIONAL ORGANIC CHEMISTRY I | IGNOU Bachelor of Science (General) (CBCS) (BSCG)

BCHCT-133—January 2026 / July 2026

CHEMICAL ENERGETICS, EQUILIBRIA AND FUNCTIONAL ORGANIC CHEMISTRY I

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BCHCT-133 Assignment Questions — January 2026

Q1. List the differences between thermodynamically reversible and irreversible processes with the suitable examples.

Q3. Two molecule of ∝ -D -glucose condense in enzyme catalyzed reaction to give a molecule of disaccharide, maltose. Calculate the enthalpy of the reaction. The enthalpies of combustion of crystalline ∝ -D -glucose and maltose at 25 °C are -2809.1 kJmol⁻¹ and 5645.5 kJmol⁻¹, respectively.

Q4. Differentiate between enthalpy driven and entropy driven reactions with the help of suitable examples. What is the chemical potential? Explain it with its significance.

Q5. In the equilibrium mixture of three ideal gases A, B, C A (g) ⇌ B (g) + C (g) obtained by dissociation of A to the extent of 20 % at a total pressure of 1.0 atm, what are the partial pressure of A, B and C.

Q6. Consider the following reaction N₂ + 3 H₂ ⇌ 2NH₃ In which direction, towards reactants and towards products, does the reaction shift if the equilibrium is stressed by each change?

Q7. Which factor affect the degree of ionization of weak electrolyte. Explain in brief. Calculate the pH of 0.010 M aqueous solution of NaOH at 25 °C.

Q8. Explain the effect of common ion on the ionization equilibrium of weak acids with the help of a suitable example. The pH of an aqueous solution of lactic acid CH₃CH(OH)COOH-a weak acid was found to be 2.7. Calculate the concentration of solution if Kₐ for lactic acid is 1.4 × 10⁻⁴.

Q9. Arrange the following salt of magnesium in the order of increasing solubilities. MgF₂, MgCO₃, Mg₃(PO₄)₂ [Given: Ksp(MgF₂) = 3.7 × 10⁻⁸; Ksp(MgF₂) = 3.5 × 10⁻⁸; and Ksp(MgF₂) = 1.0 × 10⁻²⁵ at 25 °C.]

Q11. What is Hückel rule? Define this with suitable example. How would you prepare benzene from ethyne? Write its mechanism.

Q12. What are the limitations of Friedel-Crafts alkylation reactions? Write the product of the following reactions.

Q13. Write the mechanism of chlorination of methyl benzene. Predict the reactant of the following reaction.

Q14. Arrange the following molecules in order of increasing boiling points. Give reason for this trend: CHCl₃, CH₂Cl₂, CH₃Cl, CCl₄. Complete the following reactions.

Q15. Which of the following compounds undergo Sɴ1/Sɴ2 reaction? Explain. Write the product and mechanism of the following reaction.

Q16. Complete the following reaction and write its mechanism: [image reaction OH TsCl Pyridine A Nal Acetone B]

Q17. Write the mechanism of the formation of salicylic acid from phenol.

Q18. Give two important features of the crown ethers. Write product for the following reactions.

Q19. How will you prepare primary, secondary and tertiary alcohols from same Grignard reagent?

Q20. How will you bring about following conversions?