Physical Chemistry Cheat Sheet - NEET 2027

1. Thermodynamics & Thermochemistry

Thermodynamics governs energy transformations and spontaneity in chemical systems. The following core equations represent key concepts frequently evaluated in NEET questions.

Core Principles & Mathematical Formulations

• First Law of Thermodynamics: Conservation of energy expressed as \(\Delta U = q + w\), where \(\Delta U\) is internal energy change, \(q\) is heat, and \(w\) is work done.
• Enthalpy Relation: Enthalpy \(H\) is defined by \(H = U + pV\).
• Heat Capacities:
  • Constant pressure heat capacity: \(C_p = (\frac{\partial H}{\partial T})_p\)
  • Constant volume heat capacity: \(C_v = (\frac{\partial U}{\partial T})_v\)
• Second Law & Entropy: Entropy change constraint is given by \(dS \ge \frac{\delta q}{T}\).
• Entropy Change of an Ideal Gas: \[\Delta S = nC_v \ln(\frac{T_2}{T_1}) + nR \ln(\frac{V_2}{V_1})\]
• Gibbs Free Energy & Spontaneity: Defined as \(G = H - TS\). Fundamental equation: \(dG = Vdp - SdT\).
• Maxwell Relations: \[(\frac{\partial T}{\partial V})_S = -(\frac{\partial p}{\partial S})_V, \quad (\frac{\partial S}{\partial V})_T = (\frac{\partial p}{\partial T})_V\]

2. Chemical Kinetics

Chemical kinetics deals with reaction rates, mechanism pathways, and activation energy barriers.

Reaction Orders & Arrhenius Dynamics

• First-Order Integrated Rate Law: \(\ln[A] = \ln[A]_0 - kt\) with half-life \(t_{1/2} = \frac{\ln 2}{k} \approx \frac{0.693}{k}\).
• Second-Order Integrated Rate Law: \(\frac{1}{[A]} = \frac{1}{[A]_0} + kt\) with half-life \(t_{1/2} = \frac{1}{k[A]_0}\).
• Arrhenius Equation: Expresses temperature dependence of rate constants: \[k = A e^{-E_a / RT}\] where \(E_a\) is activation energy and \(A\) is the pre-exponential frequency factor.

Activation Energy Profile Analysis

Consider a reaction coordinate diagram where reactants transition to products through a transition state requiring energy \(E_a\):

Reaction example: Dehydration of alcohols using acidic catalysts, such as converting ethanol into ethylene or substituted phenols under specific reaction conditions.

Structure of a representative phenolic compound tested in organic-physical reaction mechanism questions:

Structure: 2,4,6-Tribromophenol (formed during quantitative bromination of phenol).

3. Quantum Chemistry & Atomic Structure

Quantum mechanical models describe subatomic particles, wave-particle duality, and energy quantization.

Fundamental Quantum Relations

• Photon Energy: \(E = h u = \frac{hc}{\lambda}\)
• De Broglie Wavelength: \(\lambda = \frac{h}{p} = \frac{h}{mv}\)
• Heisenberg Uncertainty Principle: \(\Delta x \Delta p \ge \frac{\hbar}{2}\) where \(\hbar = \frac{h}{2\pi}\).
• Time-Independent Schrödinger Equation: \[\hat{H}\psi = E\psi \implies (-\frac{\hbar^2}{2m} abla^2 + V)\psi = E\psi\]
• Particle in a 1D Box (Length \(L\)): \[E_n = \frac{n^2 h^2}{8mL^2}, \quad \psi_n = \sqrt{\frac{2}{L}} \sin(\frac{n\pi x}{L})\]

4. Electrochemistry

Electrochemistry connects chemical oxidation-reduction reactions with electrical energy generation and potential differences.

Quantitative Electrochemistry Formulas

• Faraday's Laws of Electrolysis: \(Q = It = nF\) where \(F \approx 96500\text{ C/mol}\).
• Standard Cell Potential: \(E^\circ_{\text{cell}} = E^\circ_{\text{cathode}} - E^\circ_{\text{anode}}\).
• Gibbs Energy & EMF: \(\Delta G^\circ = -nFE^\circ_{\text{cell}}\).
• Nernst Equation: \[E = E^\circ - \frac{RT}{nF}\ln Q\] At \(T = 298\text{ K}\): \[E = E^\circ - \frac{0.0592}{n}\log_{10} Q\]

5. States of Matter & Colligative Properties

Behavior of real vs. ideal gases and properties of dilute solutions dependent on solute particle concentrations.

Gas Laws & Solution Thermodynamics

• Ideal Gas Law: \(pV = nRT\)
• Van der Waals Equation for Real Gases: \[(p + a\frac{n^2}{V^2})(V - nb) = nRT\] where \(a\) accounts for intermolecular forces and \(b\) accounts for molecular volume.
• Raoult's Law: Partial vapor pressure of solvent \(P_A = x_A P_A^\circ\).
• Colligative Properties (with van 't Hoff factor \(i\)):
  • Freezing Point Depression: \(\Delta T_f = i K_f m\)
  • Boiling Point Elevation: \(\Delta T_b = i K_b m\)
  • Osmotic Pressure: \(\Pi = i M R T\)

6. PYQ Analysis & NTA Pattern for NEET 2027

Understanding chapter weightage and question distribution based on historical NTA NEET trends is critical for target preparation.

Chapter Weightage & Trend Breakdown

7. Frequently Asked Questions (FAQ)