Concise Notes: Thermodynamics + States of Matter
1) Thermodynamics
a) Basic concepts
- System: part of the universe chosen for study.
- Surroundings: everything outside the system.
- Boundary: separates system and surroundings.
Types of systems
- Open system: exchanges both matter and energy.
- Closed system: exchanges energy only, not matter.
- Isolated system: exchanges neither matter nor energy.
Properties of a system
- Extensive properties depend on amount of substance: mass, volume, internal energy.
- Intensive properties do not depend on amount: temperature, pressure, density.
State and state functions
- A state is defined by measurable properties like P, V, T.
- State functions depend only on the current state, not the path: U, H, S, P, V, T.
Types of processes
- Isothermal: temperature constant.
- Adiabatic: no heat exchange.
- Isobaric: pressure constant.
- Isochoric: volume constant.
- Reversible: proceeds infinitely slowly, can be reversed exactly.
- Irreversible: real spontaneous process.
b) Heat and work
- Heat is energy transferred because of temperature difference.
- Work is energy transferred when a force acts through a distance.
- Both are path functions, not state functions.
c) First law of thermodynamics
- Energy cannot be created or destroyed, only transformed.
- \Delta U = q + w
where q = heat absorbed by system, w = work done on system.
Internal energy
- Total microscopic energy of a system.
- Depends on state only.
Enthalpy
- H = U + PV
- At constant pressure: \Delta H = q_p
Heat capacity
- Heat required to raise temperature by 1 K.
- C = \frac{q}{\Delta T}
Relation between C_p and C_v for ideal gases
Joule–Thomson effect
- Temperature change of a real gas when it expands through a porous plug or valve without heat exchange.
- Some gases cool, some heat up.
- The temperature at which inversion occurs is called the inversion temperature.
d) Second law of thermodynamics and entropy
- Not all energy conversions are possible in practice.
- Heat flows naturally from hot body to cold body.
Entropy
- Measure of randomness or disorder.
- For a reversible process:
dS = \frac{dq_{rev}}{T}
- Entropy of the universe increases for spontaneous processes.
Carnot cycle / heat engine
2) States of Matter
a) Gaseous state
Ideal gas behavior
- Obeys gas laws exactly under low pressure and high temperature.
- Assumes particles have negligible volume and no intermolecular forces.
Kinetic theory of gases: postulates
- Gas contains many tiny particles in constant random motion.
- Particle volume is negligible compared to gas volume.
- No attractive or repulsive forces between particles except during collisions.
- Collisions are perfectly elastic.
- Pressure is due to collisions with container walls.
- Average kinetic energy is proportional to absolute temperature.
Distribution of molecular speeds
- Not all gas molecules move at the same speed.
- Maxwell–Boltzmann distribution shows:
- few molecules have very low or very high speed
- most molecules have intermediate speed
- Important speeds:
- Most probable speed
- Average speed
- Root mean square speed
b) Liquid state
Liquid–vapour equilibrium / vapour pressure
- In a closed container, liquid molecules evaporate and vapour molecules condense.
- At equilibrium, rate of evaporation = rate of condensation.
- Pressure exerted by vapour at equilibrium is vapour pressure.
- Vapour pressure increases with temperature.
Surface tension
- Force acting along the surface of a liquid per unit length.
- Due to cohesive forces between liquid molecules.
- Measured using a stalagmometer by comparing drop number or drop weight.
Viscosity
- Resistance offered by a liquid to flow.
- Higher viscosity means thicker, slower flow.
- Measured using an Ostwald viscometer.
- Flow time is related to viscosity.
If you want, I can also convert this into exam-ready short answers or flashcards.