MHT-CET Chemistry · Chemical Thermodynamics and Energetics

Thermodynamic Systems, Properties and Processes

A system is the part of the universe under study; its properties are intensive (independent of amount) or extensive, and state functions (fixed by the state) or path functions (heat, work); a process is named by what it holds constant.

All Chemical Thermodynamics and Energetics notes MHT-CET Chemistry strategy

Why this matters

22 PYQs, all EASY — pure recall. The paper asks which property is intensive or extensive, which is a path function, what an isolated system is, which process keeps volume constant, and what is true or false of an isothermal or reversible process. Two short tables and five process definitions cover it.

Concept 1 of 2: Systems, Intensive Versus Extensive, State Versus Path

Halve the sample: a property that halves with it (mass, volume, U, H, S, heat capacity) is extensive; one that stays the same (temperature, pressure, density, boiling point, specific heat, surface tension) is intensive. A state function depends only on where the system is, not how it got there; heat and work depend on the route.

Definition

Open system exchanges matter and energy (beaker); closed exchanges energy only (sealed flask); isolated exchanges neither (thermos flask).
Intensive: temperature, pressure, density, boiling point, refractive index, viscosity, surface tension, specific heat, molar properties.
Extensive: mass, volume, number of moles, internal energy, enthalpy, entropy, Gibbs energy, heat capacity.
State functions: U, H, S, G, T, P, V. Path functions: heat q and work w.
Temperature is the exam's example of a property that is BOTH intensive and a state function.

Property	Intensive or extensive	State or path
Temperature, pressure	Intensive	State
Boiling point, density, surface tension, viscosity, specific heat	Intensive	State SPECIFIC heat (per gram) is intensive; HEAT CAPACITY (of the sample) is extensive.
Mass, volume, number of moles	Extensive	State
Internal energy U, enthalpy H, entropy S	Extensive	State Internal energy is the planted 'not intensive' option.
Heat capacity	Extensive	—
Heat q, work w	—	Path Work is the only path function among U, w, S, H.

Divide the sample in two and ask what changes.

Practise this conceptself-check · 4 quick reps

The same idea in a real exam question:

MHT-CET · 2023 · 2nd May Shift 1 · Q61Easy

Example 1 · Chemical Thermodynamics and Energetics · Thermodynamic Systems, Properties and Processes

Which among the following is NOT an intensive property?

Heat capacity as intensive

A bigger sample needs more heat per degree, so heat capacity is EXTENSIVE. Its per-gram version, specific heat, is intensive. The paper pairs them in one option to catch the mix-up.

Drill 6 more on systems, intensive versus extensive, state versus path

Concept 2 of 2: Isothermal, Isochoric, Isobaric, Adiabatic and Reversible

Each process fixes one thing and that fixes one term of the first law. Constant volume kills the work; constant temperature kills ΔU (ideal gas); adiabatic kills q. A reversible process is one carried out so slowly, through equilibrium states, that an infinitesimal change reverses it.

Definition

Isothermal (T constant): for an ideal gas $\Delta U = 0$ and $\Delta H = 0$ ; heat CAN flow in or out ( $q = -w$ ).
Isochoric (V constant): $w = -P_{\text{ext}}\Delta V = 0$ , so $q_V = \Delta U$ .
Isobaric (P constant): $q_P = \Delta U + P_{\text{ext}}\Delta V = \Delta H$ . Heating a gas at constant P: $V_1/T_1 = V_2/T_2$ — doubling V from 300 K needs 600 K.
Adiabatic (q = 0): $\Delta U = w$ ; temperature changes.
Reversible: infinitely slow, driving and opposing forces differ INFINITESIMALLY, mechanical equilibrium at every step, reversed by an infinitesimal change. Irreversible: finite difference, sudden, real processes.

What each process fixes

\text{isochoric: } w = 0;\quad \text{isothermal (ideal): } \Delta U = 0;\quad \text{adiabatic: } q = 0;\quad \text{isobaric: } q_P = \Delta H

Worked example

A gas at 2 dm³ and 250 K is heated at constant pressure until its volume is 5 dm³. Name the process and find the final temperature.

Practise this conceptself-check · 4 quick reps

The same idea in a real exam question:

MHT-CET · 2023 · 11th May Shift 2 · Q53Easy

Example 2 · Chemical Thermodynamics and Energetics · Thermodynamic Systems, Properties and Processes

Identify the process from following such that volume of system remains constant.

'Isothermal' read as 'no heat exchange'

That is ADIABATIC. In an isothermal process heat flows freely — it is exactly what keeps the temperature constant while the gas does work.

Drill 4 more on isothermal, isochoric, isobaric, adiabatic and reversible

Summary — formulas & gotchas at a glance

A revision cheat-sheet for the formulas and gotchas above. Click any concept name to jump back to its full explanation.

Formulas (1)

Isothermal, Isochoric, Isobaric, Adiabatic and Reversible
What each process fixes
$\text{isochoric: } w = 0;\quad \text{isothermal (ideal): } \Delta U = 0;\quad \text{adiabatic: } q = 0;\quad \text{isobaric: } q_P = \Delta H$

Reference tables (1)

Systems, Intensive Versus Extensive, State Versus Path6 rows

Property	Intensive or extensive	State or path
Temperature, pressure	Intensive	State
Boiling point, density, surface tension, viscosity, specific heat	Intensive	State SPECIFIC heat (per gram) is intensive; HEAT CAPACITY (of the sample) is extensive.
Mass, volume, number of moles	Extensive	State
Internal energy U, enthalpy H, entropy S	Extensive	State Internal energy is the planted 'not intensive' option.
Heat capacity	Extensive	—
Heat q, work w	—	Path Work is the only path function among U, w, S, H.

Divide the sample in two and ask what changes.

Watch out for (2)

Heat capacity as intensive
→ Systems, Intensive Versus Extensive, State Versus Path
'Isothermal' read as 'no heat exchange'
→ Isothermal, Isochoric, Isobaric, Adiabatic and Reversible

Test yourself on Chemical Thermodynamics and Energetics

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Related notes

Enthalpy — why q at constant pressure is ΔH →