Extensive Properties Explained Which Property Depends On Substance Amount

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Choosing the correct term to describe a property that depends solely on the amount of a substance is crucial in chemistry. Understanding the distinction between extensive and intensive properties is fundamental for grasping various chemical concepts and calculations. This article delves into the concept of extensive properties, differentiating them from intensive properties and exploring their significance in chemical systems. We will dissect the provided options—flammability, extensive, intensive, and reactivity—to definitively answer the question and solidify your understanding of this key chemical principle.

Understanding Extensive Properties

Extensive properties are those that change when the amount of substance changes. This means that if you double the amount of a substance, you double the value of its extensive properties. Think of it like this: the more you have, the bigger the extensive property gets. Classic examples of extensive properties include mass, volume, and length. Mass, the measure of how much matter is in a substance, clearly increases with the amount of substance present. Similarly, volume, the amount of space a substance occupies, directly scales with the quantity of the substance. Imagine a cup of water versus a gallon of water; the gallon has a significantly larger volume. Length is another straightforward example; a longer rope has more mass than a shorter one. Energy, particularly internal energy, is also an extensive property. A larger system possesses a greater amount of internal energy due to the increased number of particles and their associated kinetic and potential energies. The heat capacity, which is the amount of heat required to raise the temperature of a substance by a certain amount, is also an extensive property. A larger sample will require more heat to achieve the same temperature change compared to a smaller sample. Understanding extensive properties is vital in many chemical and physical applications, particularly in stoichiometry and thermodynamics, where the amounts of substances directly influence the system's behavior. In essence, extensive properties provide a quantitative way to describe how the size or extent of a system affects its characteristics.

Differentiating Extensive and Intensive Properties

To fully grasp extensive properties, it's essential to contrast them with intensive properties. Intensive properties, unlike extensive properties, do not depend on the amount of substance present. This means that whether you have a tiny droplet of water or an Olympic-sized swimming pool, certain properties will remain the same. Key examples of intensive properties include temperature, pressure, density, and color. Temperature, the measure of the average kinetic energy of the molecules in a substance, is an intensive property because it doesn't change based on the amount of substance. A cup of boiling water and a pot of boiling water will both have the same temperature, although the pot contains significantly more water and, thus, more thermal energy. Similarly, density, defined as mass per unit volume, is an intensive property. A small piece of gold and a large gold bar will have the same density, even though the bar has a much greater mass and volume. Pressure, the force exerted per unit area, is also intensive. The pressure at the bottom of a glass of water is the same regardless of whether the glass is half-full or completely full (assuming the height of the water column remains constant). Color is another intensive property; pure gold is always golden yellow, regardless of the amount. Understanding the difference between extensive and intensive properties is crucial for analyzing chemical and physical systems. While extensive properties provide information about the size or scale of the system, intensive properties reveal inherent characteristics of the substance itself. This distinction is fundamental in fields like thermodynamics, where both types of properties are used to describe the state of a system and predict its behavior.

Examining the Given Options

Now, let's analyze the options provided in the question to determine which one refers to a property that depends only on the amount of a substance:

  • A. Flammability: Flammability is the ability of a substance to burn or ignite, causing fire or combustion. This is an intensive property because it describes an inherent characteristic of the substance. A small amount of a flammable substance will ignite just as readily as a large amount, assuming the conditions are the same. The flammability of gasoline, for example, is the same whether you have a gallon or a drop. Thus, flammability is not the correct answer.
  • B. Extensive: This is the correct answer. As we've discussed, extensive properties are those that depend on the amount of substance present. Mass, volume, and length are all examples of extensive properties. The question specifically asks for a term that refers to a property dependent on the amount of substance, making "extensive" the accurate choice.
  • C. Intensive: Intensive properties, as previously explained, do not depend on the amount of substance. Temperature, density, and pressure are examples of intensive properties. Since the question seeks a property that does depend on the amount of substance, "intensive" is incorrect.
  • D. Reactivity: Reactivity refers to how readily a substance undergoes a chemical reaction. This is an intensive property because it describes an inherent characteristic of the substance. A small amount of a highly reactive substance will react in the same way as a large amount, although the overall extent of the reaction might differ. The reactivity of sodium with water, for example, is the same whether you use a small piece or a large piece. Therefore, reactivity is not the answer.

The Significance of Extensive Properties in Chemistry

Extensive properties play a critical role in various areas of chemistry. In stoichiometry, which deals with the quantitative relationships between reactants and products in chemical reactions, extensive properties like mass and volume are essential for calculations. Determining the amount of reactants needed or the amount of products formed relies heavily on understanding how these extensive properties change with the quantity of substance. For example, balancing chemical equations requires knowing the molar masses of the substances involved, which are directly related to the mass (an extensive property) of a mole of the substance. In thermodynamics, the study of energy and its transformations, extensive properties are fundamental for defining the state of a system. Internal energy, enthalpy, and entropy, which are crucial thermodynamic quantities, are all extensive properties. The amount of energy stored in a system (internal energy) and the heat exchanged during a process depend directly on the mass or volume of the system. Similarly, in solution chemistry, extensive properties are used to describe the composition of solutions. The mass or volume of a solute or solvent directly affects the overall properties of the solution, such as its concentration. In analytical chemistry, techniques like gravimetric analysis rely on measuring the mass (an extensive property) of a precipitate to determine the amount of a specific substance in a sample. Understanding extensive properties is also crucial in industrial processes where scaling up reactions and production volumes requires careful consideration of how these properties will change with the increased scale. In essence, extensive properties provide a quantitative framework for understanding and manipulating chemical systems, making them indispensable in both theoretical and applied chemistry.

Conclusion

In summary, the term that refers to a property that depends only on the amount of a substance is extensive. Extensive properties, such as mass, volume, and energy, scale directly with the quantity of the substance present. Understanding the distinction between extensive and intensive properties is crucial for grasping fundamental chemical concepts and solving a wide range of problems in chemistry. By differentiating extensive properties from intensive properties like flammability and reactivity, we can better analyze and predict the behavior of chemical systems. This knowledge forms the foundation for more advanced studies in chemistry and related fields, highlighting the importance of mastering these basic principles.