Question

# Which of the following is an extensive property?A. EnthalpyB. ConcentrationC. DensityD. Viscosity

Hint: Think about the definitions of both intensive and extensive properties. Extensive properties depend on the amount of mass present. Intensive properties are inherent and will stay the same even if the amount of mass is changed.

First let us look at the definition of intensive and extensive properties and some of their examples.
- An intensive property of a substance will not depend on the mass of the substance present. Examples include, melting point, boiling point, density, etc.
- An extensive property of a substance will change as per the changes in the amount of substance or mass of the substance. Examples include, volume, mass, energy, etc.
Now let us look at each of the given options:
- Enthalpy
Enthalpy is defined as the heat content of any given system. The amount of heat a system can hold or already contains depends on the number of chemical bonds present in the system. This implies that enthalpy is dependent on the number of molecules that are present in the system.
- Concentration
Concentration is defined as the amount of substance per unit volume. Once the concentration of a solution has been decided, it cannot be changed just by changing the total volume of the solution present in the system, either solute or solvent has to be added to change the concentration. Thus, it is an intensive property of the solution.
- Density
Density is defined as the ass per unit volume. In any substance, the degree of packing is defined by density. As the unit volume is fixed, it does not matter how much mass is taken out of the whole system, the density of that substance is going to remain the same. Thus, it is an intensive property.
- Viscosity
It is defined as the resistance experienced by two layers of molecules against the uniform flow of the fluid. This property too, is associated with sheets of molecules. But adding numerous sheets or layers of molecules on top of each other will not affect the resistance between two layers, it will remain constant. Thus, viscosity is an intensive property.

Hence, from this analysis, we can say that the extensive property among the options given is ‘A. Enthalpy’.

Note: In the option ‘B. Concentration’, remember that we are checking the property of the solution itself, not the solute or solvent. A change in the mass of the solution as a whole is not going to change the concentration of the solution, it will remain the same. If only solute or solvent is added to the solution, we will not be measuring the properties of the same solution, it will be a different solution.