Chemistry · Thermodynamics · NEET
An extensive property is one whose value depends on how much matter (how many moles or how much mass) is present. If you increase the amount of substance, the value increases. Think of it as measuring the 'extent' or total amount of something. Examples: mass, volume, enthalpy (H), internal energy (U), entropy (S), Gibbs energy (G), and heat capacity (C).
Heat capacity (C) is EXTENSIVE. It is the amount of heat needed to raise the temperature of the WHOLE sample by 1 K. A bigger sample needs more heat, so C depends on the amount of matter. But be careful: specific heat capacity (per gram) and molar heat capacity (per mole) are INTENSIVE, because dividing by mass or moles removes the amount dependence. This split is a very common NEET trap.
Enthalpy (H) is EXTENSIVE. It is defined as H = U + pV. Both internal energy U and the pV term scale with the amount of matter, so H does too. Two moles of a gas have twice the enthalpy of one mole (at the same conditions). This is why thermochemical equations must state moles: doubling the amount doubles the enthalpy change.
Volume is extensive because it directly measures how much space the matter occupies. If you take 2 litres of water and add another 2 litres, you get 4 litres. The value adds up when you combine samples. Anything that adds up like this when you combine two identical parts is extensive.
Use the 'divide-in-half' test. Imagine cutting the system into two equal halves. If the property becomes half of its original value, it is EXTENSIVE (like mass, volume, enthalpy). If it stays the SAME in each half, it is intensive (like temperature, density, pressure). Extensive properties are additive; intensive properties are not.
Yes. Internal energy U is extensive because it is the total energy stored in all the particles of the sample. More particles means more total energy. Since enthalpy H = U + pV and both U and pV are extensive, enthalpy is extensive too. For NEET, remember U, H, S, G, C, mass, volume, and moles are all extensive.
Yes, if you divide one extensive property by another extensive property (usually amount of matter). For example: volume (extensive) divided by moles gives molar volume (intensive); mass (extensive) divided by volume gives density (intensive); heat capacity (extensive) divided by mass gives specific heat (intensive). The ratio of two extensive quantities is always intensive.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Heat capacity (C) is extensive. Molar heat capacity (Cm) and specific heat capacity are intensive because they are per mole or per gram.
Yes. Both enthalpy (H) and internal energy (U) are extensive because they scale with the amount of matter. This is why thermochemical equations depend on the number of moles.
Mass, volume, enthalpy (H), internal energy (U), and heat capacity (C). Entropy (S), Gibbs energy (G), and number of moles are also extensive.
Divide the system in half. If the property halves (becomes additive), it is extensive. If it stays the same, it is intensive.
Because enthalpy change of a reaction depends on moles. If you double the amounts in a thermochemical equation, you must double the enthalpy change. Knowing H is extensive prevents calculation mistakes in NEET.
