Thermodynamics
Class 11 · Chemistry
4 ideas in Class 11 Chemistry, explained in plain words, with games and quizzes to practise.
Thermodynamic Terms and the First Law
Part of: Laws and Heat Measures
The system is the watched part; the rest is surroundings. State fixes properties; paths vary. Energy banks as internal store: heat in plus work on. Work leaving counts negative, and free expansion against nothing does none.
Why it matters. Signs and states decide every energy book. Getting them right prevents the classic lost minus.
Formulas
- First law: change in U = heat in + work on.
- Work by the system counts negative; free expansion does zero.
Key words
- System
- : The watched part; the rest is surroundings.
- Intensive variable
- : A property independent of amount, like temperature.
- Extensive variable
- : A property scaling with amount, like volume.
- State function
- : A quantity fixed by endpoints, not the path.
- Isolated system
- : No exchange of matter or energy; U and V stay fixed.
Try it in two minutes
- Name system and surroundings for tea.
- Push a syringe and sign the work.
- Expand into vacuum and count zero.
Try at home. Track heat and work for a pump squeeze.
Enthalpy and Calorimetry
Part of: Laws and Heat Measures
Enthalpy adds pressure-volume work to store; steady-pressure heat equals its change. Gas heats differ by R. Formation enthalpies from elements combine by Hess's law to price any reaction, with elements defined at zero.
Why it matters. Labels, fuels and factories all quote enthalpy. Hess's law prices the unmeasurable from the measured.
Formulas
- H = U + pV
- Cp - Cv = R for an ideal gas
- Reaction enthalpy = formations of products minus reactants.
Key words
- Enthalpy
- : Store plus pressure-volume work; steady-pressure heat equals its change.
- Hess's law
- : Formation enthalpies from elements combine to price any reaction.
- Formation enthalpy
- : Heat of forming from elements, zero for elements in standard state.
- Bond enthalpy
- : Average cost per bond from atomisation.
Try it in two minutes
- Burn a peanut under a can and estimate heat.
- Add two known reactions to get a third.
- Price ammonia formation from its elements.
Try at home. Compare fuel labels by enthalpy per gram.
Spontaneity: Entropy and Gibbs Energy
Part of: Direction, Balance and Stability
Disorder grows in spontaneous change; isolated systems maximise it. Gibbs energy subtracts temperature-weighted disorder from heat: negative means go. Heat and disorder each favour or oppose by temperature, and zero free energy marks equilibrium.
Why it matters. Direction, not just heat, picks winners. The temperature crossover table forecasts every case.
Formulas
- G = H - T S
- Crossover: T = H / S for the flip point.
- Standard G = - R T log(K)
Key words
- Spontaneous
- : Needing no outside push.
- Entropy
- : Disorder, rising in spontaneous change, priced in joules per kelvin per mol.
- Gibbs energy
- : Heat minus temperature-weighted disorder; negative means go.
- Equilibrium mark
- : Zero free energy.
Try it in two minutes
- Release scent and watch it spread.
- Freeze water and check heat versus order.
- Find the crossover temperature of a reaction.
Try at home. Mix hot and cold water and track disorder.
Stability, Mixing and Heat Flow
Part of: Direction, Balance and Stability
Positive formation enthalpy flags unstable compounds that may still persist slowly. Mixing gases raises entropy with no heat. Full journeys split into warmings, melts and boils, each billed separately; units must match across the sum.
Why it matters. Stability is thermodynamics, survival is kinetics. Splitting journeys avoids the classic missed-step error.
Formulas
- Freeze journey: cool liquid, freeze, cool ice, billed separately.
- Endothermic with rising disorder turns spontaneous at high T.
Key words
- Unstable compound
- : Positive formation enthalpy, yet possibly slow to change.
- Entropy of mixing
- : Rise from each gas gaining room.
- Heat budget
- : Full journeys split into warmings, melts and boils.
- Molar entropy units
- : Joules per kelvin per mol.
Try it in two minutes
- Flag NO as unstable yet lingering.
- Open a partition and count new arrangements.
- Bill a freeze journey step by step.
Try at home. Chill water and bill each cooling step.
What your child will practise
- Enthalpy and Calorimetry: Ocean Quick Fire (Quick Fire)
- Spontaneity: Entropy and Gibbs Energy: Jungle Puzzle (Clue Puzzle)
- Spontaneity: Entropy and Gibbs Energy: Jungle Quick Fire (Quick Fire)
- Stability, Mixing and Heat Flow: Candy Quick Fire (Quick Fire)
- Thermodynamic Terms and the First Law: Desert Puzzle (Clue Puzzle)
- Quiz: Enthalpy and Calorimetry (8 questions)
- Quiz: Spontaneity: Entropy and Gibbs Energy (8 questions)
- Quiz: Stability, Mixing and Heat Flow (8 questions)
- Quiz: Thermodynamic Terms and the First Law (8 questions)