Thermodynamics

ThermodynamicsNEET Chemistry · Class 11 · NCERT Chapter 5

Overview Notes NEET Questions Interactive Learning

2 interactive concept widgets for Thermodynamics. Drag any slider, change any number, and watch the formula and the answer update live. Built so you understand how each NEET problem actually works, not just the final number.

On this page

Gibbs free energy predictor (ΔG = ΔH − TΔS)

Hess's law step-by-step calculator (3 examples)

Gibbs free energy and spontaneity

Adjust ΔH, ΔS, and temperature to compute ΔG = ΔH − TΔS. See which of the four spontaneity cases applies and whether the reaction is product-favoured.

Thermodynamics

Gibbs free energy predictor

Adjust ΔH, ΔS, and temperature to compute ΔG = ΔH - TΔS. See spontaneity verdict and all four ΔH/ΔS case combinations.

Adjust ΔH, ΔS, and temperature T to calculate Gibbs free energy ΔG = ΔH − TΔS. See if the reaction is spontaneous.

Combustion (ΔH<0, ΔS>0)

Ice melting (ΔH>0, ΔS>0)

N₂+3H₂→2NH₃ (ΔH<0, ΔS<0)

CaCO₃ decomp (ΔH>0, ΔS>0)

ΔH (enthalpy)

-890 kJ/mol

Exothermic (heat released)

ΔS (entropy)

+243 J/mol·K

Disorder increases

Temperature (T)

298 K (25°C)

ΔG = ΔH − TΔS

= -890 − 298 × (243/1000) = -890 − (72.41) = -962.41 kJ/mol

Spontaneous

ΔG < 0: Reaction proceeds forward spontaneously.

All four cases (NEET favorites)

ΔH −, ΔS +

Always spontaneous at all T

Current

ΔH +, ΔS −

Never spontaneous at any T

ΔH −, ΔS −

Spontaneous at low T (ΔH dominates)

ΔH +, ΔS +

Spontaneous at high T (TΔS dominates)

Try this

For CaCO₃ decomposition (ΔH=+178, ΔS=+160): raise T above ~1113 K to make ΔG negative. This is the industrial process.
NH₃ synthesis: ΔH < 0 and ΔS < 0. Spontaneous at low T. But requires high T for kinetics — a classic compromise.
ΔG = 0 gives the equilibrium temperature: T_eq = ΔH/ΔS (when ΔH and ΔS have the same sign).

Hess's law calculator

Step through three classic Hess's law examples. See how target equations are built by adding and reversing known reactions, and watch ΔH combine step by step.

Thermodynamics

Hess's law step-by-step

Walk through 3 Hess's law examples step by step. See when to add or reverse each reaction and why intermediates cancel.

Hess's Law: The total enthalpy change is the same regardless of the route taken. Add or reverse intermediate reactions to reach the target.

Example 1

Example 2

Example 3

Target: Formation of CO₂ from C and O₂

C(s) + O₂(g) → CO₂(g)

ΔH = -393 kJ/mol (find by combining the steps below)

Given reactions

(1) C(s) + ½O₂(g) → CO(g) ΔH = -111 kJ/mol

(2) CO(g) + ½O₂(g) → CO₂(g) ΔH = -283 kJ/mol

Solution steps

Try this

When you reverse a reaction, its ΔH sign flips. When you multiply by a factor, ΔH multiplies too.
Hess's Law works because enthalpy is a state function -- it only depends on start and end states.
In NEET: identify which intermediates (CO, H₂O(g), CO₂) need to cancel, then decide add or reverse.

Next chapter interactive widgets

Drag, slide and recompute on the next chapter's widgets.

Previous chapter

Class 11 · Ch 4

Chemical Bonding and Molecular Structure

Open interactive widgets

Next chapter

Class 11 · Ch 6

Equilibrium

Open interactive widgets

Track Your NEET Score Across All 90 Chapters

Free 14-day trial. AI tutor, full mock tests and chapter analytics — built for NEET 2027.

Free 14-day trial · No credit card required