Which Of These Is An Extensive Property Of A Substance

Which of These is an Extensive Property of a Substance? Understanding Extensive vs. Intensive Properties

Choosing between extensive and intensive properties can be tricky, especially when you're first learning about them. This comprehensive guide will delve deep into the difference, providing clear examples and explanations to solidify your understanding. We'll explore what makes a property extensive, clarifying the key distinctions from intensive properties. By the end, you'll confidently identify extensive properties and understand their significance in chemistry and physics.

What are Extensive Properties?

Extensive properties are physical properties of a substance that depend on the amount of matter present. This means that if you increase the amount of substance, the extensive property will also increase proportionally. Conversely, if you decrease the amount of substance, the extensive property will decrease proportionally. Think of it this way: the extensive property scales with the size of the system.

Key characteristics of extensive properties:

• Additivity: The value of an extensive property for a combined system is the sum of the values for its individual parts. For example, the mass of two blocks of gold is the sum of the individual masses of each block.
• Dependence on Size/Amount: The magnitude of the extensive property directly relates to the amount of the substance. A larger sample will have a larger value for the extensive property.
• Not Useful for Identifying Substances: Extensive properties cannot be used to identify a specific substance because they change with the amount of the substance.

What are Intensive Properties?

To fully grasp extensive properties, it's crucial to understand their counterpart: intensive properties. Intensive properties are independent of the amount of matter present. This means that the value of an intensive property remains constant regardless of the size of the sample.

Key characteristics of intensive properties:

• Non-Additivity: The value of an intensive property does not change when systems are combined. For instance, the temperature of two cups of water will not change significantly when mixed.
• Independent of Size/Amount: The magnitude of the intensive property is unaffected by the amount of substance. A small drop of water and a large bucket of water have the same density (under the same conditions).
• Useful for Identifying Substances: Intensive properties are characteristic of a substance and can be used to identify it. For example, melting point and boiling point are intensive properties.

Examples of Extensive Properties: A Detailed Look

Let's explore some common examples of extensive properties, providing detailed explanations to strengthen your understanding:

1. Mass: The Fundamental Extensive Property

Mass is arguably the most fundamental extensive property. It represents the amount of matter contained within a substance. A larger sample of a substance will inevitably have a greater mass. If you double the amount of substance, you double its mass. This straightforward relationship highlights the essence of an extensive property.

2. Volume: The Space Occupied

Volume is another quintessential extensive property. It measures the three-dimensional space occupied by a substance. A larger amount of a substance will occupy a larger volume. Just like mass, volume scales directly with the amount of substance. Consider a liter of water versus ten liters – the volume increases tenfold with the increase in the amount of water.

3. Length: A One-Dimensional Extensive Property

While often overlooked, length is an extensive property, particularly when considering the dimensions of an object. The length of a wire, the height of a building, or the diameter of a sphere all scale directly with the amount of material used to construct them.

4. Energy: A Crucial Extensive Property in Physics and Chemistry

Energy, in its various forms (kinetic, potential, thermal, etc.), is an extensive property. The total energy of a system increases with the amount of matter within that system. A larger object moving at the same velocity possesses more kinetic energy than a smaller object. Similarly, a larger quantity of a substance at a given temperature holds more thermal energy.

5. Heat Capacity: The Extensive Property of Heat Absorption

Heat capacity is a measure of how much heat energy a substance can absorb for a given temperature change. A larger sample of a substance requires more heat energy to raise its temperature by the same amount. Therefore, heat capacity is directly proportional to the mass of the substance and is hence an extensive property.

6. Enthalpy: A Thermodynamic Extensive Property

Enthalpy (H), a thermodynamic property, represents the total heat content of a system. Like heat capacity, enthalpy is directly dependent on the amount of substance, making it an extensive property. A larger reaction involving a greater amount of reactants will have a larger enthalpy change.

7. Entropy: Extensive Property in Thermodynamics

Entropy (S), a measure of disorder or randomness within a system, is also an extensive property. A larger system with more molecules will have greater entropy than a smaller system with fewer molecules. The extent of disorder increases with the amount of matter.

8. Number of Moles: A Directly Proportional Extensive Property

The number of moles (n) directly represents the amount of substance. As such, it is, by definition, an extensive property. Doubling the number of moles doubles the amount of substance.

Distinguishing Extensive from Intensive Properties: Practical Examples

Let's solidify your understanding by comparing extensive and intensive properties in practical scenarios:

Scenario 1: A Block of Ice

• Extensive: Mass (increases with the size of the ice block), Volume (increases with the size of the ice block)
• Intensive: Density (remains constant regardless of the size of the ice block), Melting point (remains constant regardless of the size of the ice block)

Scenario 2: A Sample of Copper Wire

• Extensive: Length (increases with the length of the wire), Mass (increases with the length and thickness of the wire)
• Intensive: Density (remains constant assuming the same purity and structure), Electrical conductivity (remains constant assuming the same purity and structure)

Scenario 3: A Cup of Coffee and a Thermos of Coffee

• Extensive: Volume (the thermos holds a larger volume than the cup), Mass (the thermos contains more coffee and hence more mass)
• Intensive: Temperature (both, if at the same temperature, have the same temperature), Concentration (both, if prepared using the same ratio, have the same concentration)

Importance of Understanding Extensive and Intensive Properties

The distinction between extensive and intensive properties is crucial in various scientific fields. Understanding this distinction is essential for:

• Correctly interpreting experimental data: Knowing which property is extensive or intensive dictates how you analyze and interpret data.
• Developing and applying thermodynamic concepts: Many thermodynamic calculations rely on the distinction between extensive and intensive properties.
• Engineering design and material science: Understanding these properties is critical in material selection and design processes.
• Chemistry and Physics: The concepts are fundamental to many areas within these disciplines.

Conclusion: Mastering Extensive Properties

By now, you should have a robust understanding of extensive properties, their defining characteristics, and how they differ from intensive properties. Remember, extensive properties always depend on the amount of matter, while intensive properties remain constant regardless of the sample size. This knowledge is paramount to mastering fundamental concepts in chemistry and physics and interpreting experimental data accurately. Continue to practice identifying extensive and intensive properties in various scenarios to solidify your understanding and build a strong foundation in scientific principles.