PREPWISER.
Practise online

Chemical Thermodynamics revision notes

Every idea in the Chemical Thermodynamics chapter for JEE Main, with the usual mistakes and the fast methods. Topic 1 is open to everyone; sign in free to read all 25 and download the PDF.

Sign in to read all 25Download PDF

Read the first part free. Sign in free with Google to read the rest and download the PDF: 13 A4 pages.13 A4 pages, ready to print.

How we count: 7× asked means 7 past JEE Main questions in the PrepWiser bank needed that concept, and "last" is the latest year one appeared. ★ marks ideas asked 8 or more times.

System, state functions and the first law

System, surroundings and properties
1× asked, last 2023
intensive=extensiveextensive:Vm=Vn,ρ=mV,Cm=Cn\text{intensive} = \frac{\text{extensive}}{\text{extensive}}:\quad V_m = \frac{V}{n},\quad \rho = \frac{m}{V},\quad C_m = \frac{C}{n}
Open: matter and energy cross the boundary; closed: energy only; isolated: neither. Extensive values scale with amount.
matterenergyopenenergyclosedisolated
Open: matter and energy cross; closed: energy only; isolated: neither
  • Extensive: mass, VV, UU, HH, SS, GG, heat capacity. Intensive: TT, pp, density, molar and specific quantities, surface tension. Processes: isothermal, isobaric, isochoric, adiabatic, cyclic.
State and path functions
4× asked, last 2026
∮dU=∮dH=∮dS=∮dG=0,q, w depend on the path\oint dU = \oint dH = \oint dS = \oint dG = 0,\qquad q,\ w \text{ depend on the path}
State function: fixed by the state alone (U,H,S,G,p,V,TU, H, S, G, p, V, T). Its change over any cycle is zero; q+wq+w is path-independent.
VVppOXYpath 2path 1
Same X → Y, different areas: ww and qq differ, ΔU\Delta U does not
VVppOarea =∣w∣=|w|clockwise: w=−w=-area, q=+q=+area
Cycle: ΔU=0\Delta U=0, so q=−wq=-w
  • Not the same ww on a different return path. Only ΔU\Delta U simply reverses. If X→Y has q=+10q=+10 J and w=−18w=-18 J (ΔU=−8\Delta U=-8 J), a return with q=−6q=-6 J needs w=ΔU−q=8+6=+14w=\Delta U-q=8+6=+14 J.
  • Quick method. Cycle on a pp–VV plot (pp up, VV across): ΔU=0\Delta U=0 and ∣w∣|w| = enclosed area. Clockwise: the gas does net work, so w=−areaw=-\text{area}, q=+areaq=+\text{area}. Anticlockwise: both signs reverse.
First law and the chemistry sign convention
6× asked, last 2026
ΔU=q+w,w=−pext ΔV\Delta U = q + w,\qquad w = -p_{\text{ext}}\,\Delta V
IUPAC/NCERT: q>0q>0 heat absorbed, w>0w>0 work done ON the system. Expansion gives w<0w<0. Isolated system: ΔU=0\Delta U=0.
systemΔU=q+w\Delta U=q+wq>0q>0 inw>0w>0 done ON itout: <0<0absorbs 150 J, does 200 J: ΔU=150−200=−50\Delta U=150-200=-50 J
Expansion work is done BY the gas, so w<0w<0; never q+pΔVq+p\Delta V
  • Not the physics convention. Physics writes ΔU=q−W\Delta U=q-W with WW done BY the gas. Here ww is done ON the system, so ΔU=q+w=q−pΔV\Delta U=q+w=q-p\Delta V, never q+pΔVq+p\Delta V. Doing 200 J while absorbing 150 J: ΔU=−50\Delta U=-50 J.

Practise Chemical Thermodynamics questions as you read. Free, and you can start without signing up.

Practise Chemical Thermodynamics

22 more concepts in 6 topics

Work in ideal-gas processes; Enthalpy, heat capacity and calorimetry; Thermochemistry and Hess's law; Bond enthalpy and the Born–Haber cycle; Entropy and the second law; and Gibbs energy, spontaneity and equilibrium. Read the first part free. Sign in free with Google to read the rest and download the PDF.

Sign in to read the restYou come straight back to this spot.Download the PDF

Work in ideal-gas processes

  • Work against a constant external pressure12×
  • Reversible isothermal work10×
  • Adiabatic change of an ideal gas4×
  • Comparing work on different paths8×

Enthalpy, heat capacity and calorimetry

  • Enthalpy: ΔH and ΔU17×
  • Heat capacity and Cp − Cv9×
  • Calorimetry9×
  • Enthalpy of neutralisation7×
  • Phase changes and sublimation6×

Thermochemistry and Hess's law

  • Standard enthalpy of formation8×
  • Enthalpy of combustion12×
  • Hess's law12×
  • Enthalpy of solution and hydration5×
  • Endothermic and exothermic changes3×

Bond enthalpy and the Born–Haber cycle

  • Reaction enthalpy from bond enthalpies11×
  • Born–Haber cycle and lattice enthalpy5×
  • Also remember1

Entropy and the second law

  • Entropy and the second law6×
  • Entropy of phase change and heating4×
  • Predicting the sign of ΔS3×

Gibbs energy, spontaneity and equilibrium

  • Gibbs energy and spontaneity13×
  • Four sign cases and crossover temperature15×
  • ΔG° and the equilibrium constant9×

Practise Chemical Thermodynamics next

About 160 past JEE Main questions from this chapter, with instant answer checking and step-by-step solutions where available. Free, and you can start without signing up.

Practise Chemical Thermodynamics

Also free on PrepWiser

Spotted a mistake? Write to support@prepwiser.in and we will fix it in the next version.

Version 1, October 2026. Free to share for study, as it is. Please don't sell it or remove the PrepWiser name.

PractiseSign in to read all 25Download PDF
Free with Google, takes a few seconds13 pages, free