How to Identify Intensive and Extensive Properties in Chemistry
In the physical definition of any matter, most of the physical properties are subdivided into intensive and extensive properties. The identity and function of any substance or system are defined by these properties. Let us have a look at these two sub-categories in detail.
What is an Intensive Property?
Intensive properties of any matter are those physical properties that are independent of the mass of the substance or the system. Intensive properties are also known as bulk properties. Most intensive properties are used to define the identity of that substance or system.
Intensive Property Examples
Pressure (P), temperature (T), color are all intensive properties. Other examples include density, melting point, boiling point, etc. All these parameters do not change with the mass of the body. For example, the melting point of 1 kg ice and 1 gm of ice is the same= 0ᴼC.
Chemical potential, refractive index, specific heat capacity, thermal conductivity, viscosity are all examples of intensive properties.
What is an Extensive Property?
Extensive properties of any matter are those physical properties that depend on the mass of that matter. These properties are proportional to the size or mass of the system.
Extensive Property Examples
The weight of the system increases with the mass. Similarly, the volume also increases with the mass of the substances. The heat capacity is directly proportional to the mass of a system. The energy stored in a system is dependent on the mass of the system. For example, two boxes of the same material but the different weights will also differ in their properties.
Some other examples of extensive properties are enthalpy, entropy, Gibb’s energy, internal energy, etc.
Differences between Extensive and Intensive Properties
How to Differentiate between Intensive and Extensive Properties?
It is easy to distinguish between intensive and extensive properties. One needs to double the mass of the system. The physical properties that change with an increase in mass are extensive properties. However, those physical properties that do not change with an increase in mass are intensive properties.
Other Examples of Properties
Both the intensive and extensive properties are useful in understanding the thermodynamics of a system. Thermodynamics is the study of the flow and transformation of heat forms of any matter. It depends on the matter and the factors determining its state. Parameters that define the thermodynamic properties are:
Path function- the parameter defined by the path taken by the matter or the system to reach the current state. Work done due to frictional force is an example of path function.
State functions, also known as state variables, are defined by the current state, and not the path that is taken to reach that state. Temperature is an example of state function.
The state function of the system depends on the initial and final position of the system. However, the path functions of the system depend on the path taken by the system to reach from the initial to the final state. Both the state and path functions are important parameters to study the thermodynamic properties of a system.
FAQs on Intensive and Extensive Properties of Matter: Key Differences
1. What is the fundamental difference between intensive and extensive properties of matter?
The fundamental difference lies in their dependence on the amount of substance. Intensive properties, such as temperature or density, do not depend on the quantity of matter present. In contrast, extensive properties, like mass and volume, are directly proportional to the amount of substance in the system. For example, a litre of water and a drop of water have the same boiling point (intensive), but different masses (extensive).
2. What defines an intensive property? Please provide some common examples.
An intensive property is a physical property of a system that does not change when the size of the system changes. It is a characteristic of the substance itself, regardless of how much you have. Common examples of intensive properties include:
- Temperature (T)
- Density (ρ)
- Pressure (P)
- Boiling Point and Melting Point
- Refractive Index
- Concentration
3. What is an extensive property? Can you list some examples?
An extensive property is a property that depends on the amount of matter in a sample. Its value is additive for subsystems. If you combine two identical systems, the value of an extensive property will double. Key examples include:
- Mass (m)
- Volume (V)
- Length
- Internal Energy (U)
- Enthalpy (H)
- Heat Capacity
4. Why is it important in chemistry to classify properties as intensive or extensive?
This classification is crucial in thermodynamics and material science for several reasons. Intensive properties are used to identify and characterise substances (e.g., density or melting point can help identify an unknown sample). Extensive properties are essential for quantifying how much of a substance is present and for calculations involving energy and mass balances in chemical reactions. This distinction helps define the state of a system; for example, the state of a simple compressible system is fully specified by one extensive property (like mass) and two independent intensive properties (like temperature and pressure).
5. How can an intensive property be created from two extensive properties?
An intensive property can often be derived by taking the ratio of two extensive properties. This is a key concept in chemistry. The most common example is density. Density (an intensive property) is calculated by dividing the mass of a substance (an extensive property) by its volume (another extensive property). Since both mass and volume scale with the size of the system, their ratio remains constant for a given substance under specific conditions.
6. Is temperature an intensive or extensive property? Explain the reasoning.
Temperature is a classic example of an intensive property. The reasoning is that temperature measures the average kinetic energy of the particles in a system, not the total amount of energy. If you have a pot of boiling water at 100°C and you take out a cup of water from it, the water in the cup will also be at 100°C. Even though the mass and volume (extensive properties) have been reduced, the temperature remains the same.
7. Can you provide a summary table comparing intensive and extensive properties?
Certainly. Here is a comparison of the key differences between intensive and extensive properties:
- Definition: Intensive properties are independent of the amount of substance, while extensive properties are dependent on it.
- Dependence on Size: Intensive properties do not depend on system size. Extensive properties are directly proportional to system size.
- Additivity: Intensive properties are not additive. If you mix two identical systems, the intensive property (like temperature) stays the same. Extensive properties are additive (e.g., total mass is the sum of individual masses).
- Examples: Intensive includes density, pressure, and temperature. Extensive includes mass, volume, and energy.
- Identification: The ratio of two extensive properties results in an intensive property (e.g., Mass/Volume = Density).
8. Are there any properties that are considered neither intensive nor extensive?
Yes, while the intensive/extensive classification is very useful, it doesn't cover every physical property. Some properties do not scale linearly with the size of the system and therefore do not fit neatly into either category. For instance, the resistance of a wire is extensive (longer wire, more resistance), but the resistivity is intensive. However, a property like the square root of the volume is neither intensive nor extensive. This shows that the classification is a model that works for most, but not all, thermodynamic properties.
