NEET Physics: Waves – NCERT Masterclass & 100 MCQ Quiz

THERMODYNAMICS (CHEMISTRY)

NCERT Masterclass & NEET Study Module

1. System, Surroundings & State Functions

System: The part of the universe under observation.
Surroundings: Everything else in the universe. System + Surroundings = Universe.

State Functions: Properties whose values depend only on the initial and final state, not the path taken (e.g., $P, V, T, U, H, S, G$).
Note: Work ($w$) and Heat ($q$) are Path Functions.

Intensive vs Extensive: Intensive properties do NOT depend on quantity (e.g., Temperature, Pressure, Density, Molarity). Extensive properties depend on quantity (e.g., Mass, Volume, Enthalpy, Entropy).

2. First Law of Thermodynamics & IUPAC Convention

The energy of an isolated system is constant. $\Delta U = q + w$

🔥 IUPAC Sign Conventions (Crucial for Chemistry):

• $q$ is positive ($+$) if heat is absorbed BY the system.
• $q$ is negative ($-$) if heat is released BY the system.
• $w$ is positive ($+$) if work is done ON the system (Compression).
• $w$ is negative ($-$) if work is done BY the system (Expansion).

Work Done: $w = -P_{ext} \Delta V$.
For Reversible Isothermal Expansion: $w = -2.303 nRT \log \left(\frac{V_f}{V_i}\right) = -2.303 nRT \log \left(\frac{P_i}{P_f}\right)$

3. Enthalpy ($H$) and Heat Capacity ($C$)

Enthalpy $H = U + PV$.
Change in enthalpy: $\Delta H = \Delta U + P\Delta V$ (at constant P).
For gaseous reactions: $\Delta H = \Delta U + \Delta n_g RT$, where $\Delta n_g = (\text{moles of gaseous products}) - (\text{moles of gaseous reactants})$.

Heat Capacity at constant volume: $q_v = C_v \Delta T = \Delta U$
Heat Capacity at constant pressure: $q_p = C_p \Delta T = \Delta H$
Mayer's Relation: $C_p - C_v = R$ (for 1 mole of ideal gas)

4. Thermochemistry & Hess's Law

Hess's Law of Constant Heat Summation: The total enthalpy change for a reaction is the same whether it occurs in one step or in multiple steps. It relies on the fact that Enthalpy ($H$) is a state function.

Standard Enthalpy of Formation ($\Delta_f H^\ominus$): Enthalpy change when 1 mole of a compound is formed from its constituent elements in their standard reference states. (Note: $\Delta_f H^\ominus$ of reference state elements like $O_2(g), C(graphite)$ is ZERO).

Reaction Enthalpy $\Delta_r H^\ominus = \sum \Delta_f H^\ominus(\text{products}) - \sum \Delta_f H^\ominus(\text{reactants})$

5. Entropy ($S$) and Spontaneity (Second Law)

Entropy is a measure of randomness or disorder in the system. $\Delta S = \frac{q_{rev}}{T}$.

Second Law: The entropy of the universe always increases in the course of every spontaneous (natural) change. $\Delta S_{total} = \Delta S_{sys} + \Delta S_{surr} > 0$.

6. Gibbs Free Energy ($G$)

Provides a single criterion for spontaneity using only the system's properties. $G = H - TS$.

$$\Delta G = \Delta H - T \Delta S$$

Standard Free Energy and Equilibrium: $\Delta G^\ominus = -RT \ln K = -2.303 RT \log K$

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🚀 NEET THERMODYNAMICS MEGA QUIZ (100 MCQ)

Solve the 5 parts below to master Internal Energy, Hess's Law, and Spontaneity.

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