Chemistry · Thermodynamics · NEET
NCERT defines it clearly: a molar property χm is the value of an extensive property χ of the system for 1 mole of the substance. You take a size-dependent property (like total volume or total heat capacity) and squeeze it down to a per-mole number. The formula is χm = χ / n, where n is the number of moles. So a molar property is just 'that property, but for one mole only.'
It is intensive. This confuses students because you START from an extensive property (χ). But dividing by moles (n) cancels out the amount of matter. NCERT states χm = χ/n is 'independent of the amount of matter.' Whether you have 1 mole or 100 moles of water, its molar volume Vm is the same number. For NEET, remember: any 'molar' or 'specific' or 'per unit' property is intensive.
Molar volume Vm is the volume of exactly 1 mole of a substance, Vm = V / n. For an ideal gas at STP, Vm is about 22.4 L/mol. Molar heat capacity Cm is the heat needed to raise the temperature of 1 mole by 1 kelvin, Cm = C / n. Both come from big extensive properties (total V, total heat capacity C) but are reported per mole, so both are intensive.
An extensive property (like total volume V, total enthalpy H, total heat capacity C) grows when you add more matter. A molar property is that same property divided by moles, so it stops growing with amount. If you cut a sample in half, its total volume halves (extensive), but its molar volume stays the same (intensive/molar). Molar = 'extensive property per 1 mole.'
Think of the container example from NCERT: split a gas into two equal halves. The total volume V halves and moles n halve too. But their ratio V/n does not change, because both numerator and denominator drop by the same factor. That is why Vm = V/n stays constant. Any ratio of two extensive quantities that scale together becomes intensive.
Molar mass (mass per mole, g/mol) follows the same logic and is intensive because it does not depend on how much sample you have. NEET treats 'per mole' quantities as intensive. But note: molar mass is a fixed property of the substance itself, not a thermodynamic state property like Vm or Cm. For the exam, the key point tested is that 'per mole' quantities do NOT change with sample size.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Intensive. Molar volume Vm = V/n is the volume per mole. Because you divide by moles, it does not depend on how much substance you have, so it is intensive.
χm = χ / n, where χ is an extensive property (like volume or heat capacity) and n is the number of moles. Examples: Vm = V/n and Cm = C/n.
Heat capacity C depends on how much matter you have, so it is extensive. But molar heat capacity Cm = C/n is 'per mole,' and dividing by moles cancels the amount dependence, making Cm intensive.
About 22.4 L/mol (22,400 cm3/mol) at 0 degrees C and 1 atm. It is the same for any ideal gas because it is a per-mole (intensive) quantity.
They are similar ideas. A molar property is 'per mole' (divide by n), while a specific property is 'per unit mass' (divide by mass). Both are intensive because they remove the amount dependence.
