Problem 44 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Identify the intensive quantities from the following: (a) Enthalpy (b) Temperature (c) Volume (d) Refractive Index

Step-by-Step Solution

Answer

(b) Temperature and (d) Refractive Index are intensive quantities.

Step 1: Understand Intensive and Extensive Quantities

Intensive quantities are those that do not depend on the size or extent of the system, such as temperature, pressure, and density. Extensive quantities, on the other hand, are dependent on the system size, such as volume and mass.

Step 2: Analyze Option (a): Enthalpy

Enthalpy is an extensive quantity because it depends on the amount of substance present. If you double the amount of substance, enthalpy also doubles. Therefore, it is not an intensive quantity.

Step 3: Analyze Option (b): Temperature

Temperature is an intensive quantity because it does not change when the size of the system changes. Regardless of how much substance you have, the temperature remains the same.

Step 4: Analyze Option (c): Volume

Volume is an extensive quantity because it increases proportionally with the amount of substance. Larger quantities will have larger volumes, indicating dependence on system size.

Step 5: Analyze Option (d): Refractive Index

Refractive Index is an intensive property because it is a ratio and does not depend on the amount of the material. It remains constant regardless of how much material you have.

Key Concepts

Intensive Quantities

When discussing physical quantities in chemistry, it's important to understand the difference between intensive and extensive properties. Intensive quantities are properties that remain constant regardless of the amount of material present. These characteristics provide valuable information about the nature of materials, independent of their size or volume.
For instance, temperature and refractive index are classic examples of intensive quantities. Temperature measures the average kinetic energy of particles and remains unchanged whether you are dealing with a drop of water or a whole ocean. Similarly, the refractive index, which measures how much light bends when entering a material, is uniform throughout any quantity of the material.
Recognizing that intensive properties do not scale with the size of the system helps chemists and scientists to categorize substances and predict their behaviors under different conditions. This inherent quality makes them useful tools for identification and comparison across different samples.

Extensive Quantities

Extensive quantities, in contrast to intensive properties, depend on the system's size or the amount of matter present. These properties scale directly with the quantity of material, making them crucial for understanding the total amount of substance and energy in a system.
Common examples of extensive quantities include enthalpy and volume. Enthalpy, which can be thought of as the heat content of a system, increases linearly as the quantity of material increases. If you double the amount of substance, you also double its enthalpy. Volume works similarly; it measures the three-dimensional space occupied and is directly proportional to the system's extent.
This dependence on system size means that extensive properties should be used carefully when comparing systems of differing sizes. To gain meaningful insights, extensive properties are often converted to intensive properties, enabling fair comparisons.

Physical Properties in Chemistry

Physical properties in chemistry are critical for analyzing and understanding substances without changing their chemical identities. They include a wide range of characteristics that can be measured or observed, such as color, density, boiling point, and conductivity.
These properties are divided into intensive and extensive categories. Understanding the distinction allows chemists to predict how substances will behave in various scenarios.
Physical properties, like boiling point and density, are intensive properties as they remain constant regardless of sample size. They are useful identifiers and can help in separating compounds through processes like distillation and chromatography.
On the other hand, extensive properties such as mass and volume offer insights into the total "amount" present in a given system. In practical applications, this becomes critical when considering energy transfer or conducting reactions that depend on amounts of reactants or products.
Whether intensive or extensive, these physical properties form the backbone of experimental protocols and theoretical modeling in chemistry.