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Cheat sheet · Class 11 · CBSE · Science Chemistry

Thermodynamics cheat sheet

The whole chapter on one page: key formulas, facts and the points to remember, for quick revision before a test.

CBSE Class 11 · Chemistry

Cheat sheet

Chapter 5Thermodynamics

ΔG = ΔH − TΔS: negative ΔG means spontaneous.

1. Basics

  • System types: open, closed, isolated.
  • State functions: U, H, S, G (path independent). q and w are path functions.
  • Extensive (mass, V, H) vs intensive (T, P, density).

2. First Law

ΔU=q+w\Delta U = q + w
w=−pextΔVw = -p_{ext}\Delta V
ΔH=ΔU+ΔngRT\Delta H = \Delta U + \Delta n_g RT

Chemistry sign convention: work done ON the system is positive.

3. Enthalpy Changes

Hess's law

Total ΔH is the same whatever the route — add equations like algebra.

Formation

ΔrH∘=∑ΔfH∘(products)−∑ΔfH∘(reactants)\Delta_r H^\circ = \sum\Delta_f H^\circ(\text{products}) - \sum\Delta_f H^\circ(\text{reactants})

Bond enthalpy

ΔrH=∑BE(reactants)−∑BE(products)\Delta_r H = \sum BE(\text{reactants}) - \sum BE(\text{products})

Others: combustion, atomisation, lattice (Born–Haber cycle), solution.

4. Spontaneity

ΔG=ΔH−TΔS\Delta G = \Delta H - T\Delta S
ΔG∘=−RTln⁡K\Delta G^\circ = -RT\ln K
ΔHΔSSpontaneous?
−
at all T
−never
−−at low T
at high T

5. Key Points

  • Heat capacity: Cp − Cv = R.
  • ΔS_total > 0 for spontaneous change.
  • Exothermic: ΔH < 0.
  • Third law: S = 0 for perfect crystal at 0 K.

Remember: ΔU = q + w | ΔH = ΔU + Δn_g RT | Hess | ΔG = ΔH − TΔS

Thermodynamics: questions and notes

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