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Module 2 · NEET Chemistry

Physical Chemistry

Mole concept, atomic structure, chemical bonding, thermodynamics, equilibrium.
Mole Concept · Atomic Structure · Bonding · Equilibrium · Kinetics
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Learning Objectives

  • Understand the fundamental concepts of Physical Chemistry
  • Apply key formulas and techniques to solve problems
  • Practice with exam-level questions to build speed and accuracy

Key Concepts

What is Physical Chemistry?

Physical chemistry combines principles of physics and chemistry to study the physical properties of molecules, the forces that act upon them, and the energy changes that accompany chemical reactions. For NEET, key topics include mole concept, thermodynamics, chemical kinetics, equilibrium, electrochemistry, and solutions. Mastering numerical problem-solving is essential for this branch.

Key Concepts

Mole Concept: Number of moles n = mass/molar mass = N/NA = V/22.4 L (at STP). Thermodynamics: ΔH = ΔU + ΔnRT. Chemical Kinetics: Rate = k[A]x[B]y, Arrhenius equation k = Ae-Ea/RT. Chemical Equilibrium: Kc = [C]c[D]d/[A]a[B]b. Electrochemistry: Nernst equation E = E° - (0.0591/n) log Q. Solutions: Molarity = moles/L, molality = moles/kg solvent, Raoult's law P = P°X.

Solved Examples

Example 1
Calculate the number of molecules in 36 g of water. (NA = 6.022 × 1023)

a) 6.022 × 1023 b) 1.204 × 1024 c) 3.011 × 1023 d) 2.408 × 1024
Solution: Molar mass of water = 18 g/mol. Number of moles = 36/18 = 2 moles. Number of molecules = 2 × 6.022 × 1023 = 1.204 × 1024. Hence option (b) is correct.
Example 2
The rate constant of a reaction is 2.0 × 10-3 s-1 at 300 K and 8.0 × 10-3 s-1 at 320 K. Find the activation energy. (R = 8.314 J/mol-K)

a) 55.4 kJ/mol b) 27.7 kJ/mol c) 42.1 kJ/mol d) 33.6 kJ/mol
Solution: Using the two-point form of Arrhenius equation: log(k2/k1) = Ea/(2.303R)(1/T1 - 1/T2). log(8/2) = Ea/(2.303 × 8.314)(1/300 - 1/320). log(4) = Ea/19.147 × (0.00333 - 0.003125). 0.602 = Ea/19.147 × 0.0002083. Ea = (0.602 × 19.147)/0.0002083 = 55360 J/mol = 55.4 kJ/mol. Hence option (a) is correct.
Example 3
Calculate the pH of a 0.01 M HCl solution.

a) 1 b) 2 c) 3 d) 4
Solution: HCl is a strong acid that dissociates completely. [H+] = 0.01 M = 10-2 M. pH = -log[H+] = -log(10-2) = 2. Hence option (b) is correct.

Shortcut Techniques

  • For pH calculations: pH + pOH = 14, and [H+][OH-] = 10-14 at 25°C.
  • For mole concept problems, always convert given quantities to moles first before applying stoichiometric ratios.
  • For first-order kinetics, the half-life is independent of initial concentration: t1/2 = 0.693/k.
  • In electrochemistry, remember that oxidation occurs at anode and reduction at cathode. The mnemonic is AnOx-RedCat.
Pro Tip
For NEET, practice logarithm values of common numbers (log 2 = 0.301, log 3 = 0.477, log 5 = 0.699). These will save precious time in pH and Nernst equation problems.

Application-Based Learning

Connect concepts to real-world applications: Why sky is blue (Rayleigh scattering), how pressure cookers work, why apples turn brown (oxidation).

Problem-Solving Methodology

1) Identify given data. 2) Recall formulas. 3) Check unit consistency. 4) Solve step-by-step. 5) Verify through estimation.

Pro Tip
Check if your answer is reasonable through order-of-magnitude estimation to catch gross errors.

Application-Based Learning

Connect concepts to real-world applications: Why sky is blue (Rayleigh scattering), how pressure cookers work, why apples turn brown (oxidation).

Problem-Solving Methodology

1) Identify given data. 2) Recall formulas. 3) Check unit consistency. 4) Solve step-by-step. 5) Verify through estimation.

Pro Tip
Check if your answer is reasonable through order-of-magnitude estimation to catch gross errors.

Application-Based Learning

Connect concepts to real-world applications: Why sky is blue (Rayleigh scattering), how pressure cookers work, why apples turn brown (oxidation).

Problem-Solving Methodology

1) Identify given data. 2) Recall formulas. 3) Check unit consistency. 4) Solve step-by-step. 5) Verify through estimation.

Pro Tip
Check if your answer is reasonable through order-of-magnitude estimation to catch gross errors.

Application-Based Learning

Connect concepts to real-world applications: Why sky is blue (Rayleigh scattering), how pressure cookers work, why apples turn brown (oxidation).

Problem-Solving Methodology

1) Identify given data. 2) Recall formulas. 3) Check unit consistency. 4) Solve step-by-step. 5) Verify through estimation.

Pro Tip
Check if your answer is reasonable through order-of-magnitude estimation to catch gross errors.

Practice Questions

Organic Chemistry →