Question

The enthalpy change for a reaction is a state function and it is an extensive property. Explain.

Short answer

The enthalpy change (\(ΔH\)) for a reaction is a state function because it depends only on the initial and final states of the system and is independent of the path taken during the reaction process. It can be demonstrated by Hess's Law, which states that the overall enthalpy change of a reaction is the same, regardless of the individual steps or reactions involved. Additionally, enthalpy change is an extensive property because it depends on the quantity of matter in the system. When the amount of reactants changes, the overall enthalpy change will also change, making it directly proportional to the quantity of matter involved.

Step-by-step solution

Definition of State Function

A state function is a property of a system that depends only on its current state and is independent of the path taken to reach that state. This means that the value of a state function is determined by the initial and final states of a chemical reaction and not on the specific steps taken during the reaction process.

Definition of Extensive Property

An extensive property is a property of a system that depends on the quantity of matter in the system. This means that an extensive property is directly proportional to the size or amount of the substances involved in a reaction. Examples of extensive properties include mass, volume, and enthalpy.

Enthalpy Change as a State Function

Enthalpy change (\(ΔH\)) is the amount of heat absorbed or released during a chemical reaction under constant pressure conditions. \(ΔH\) is a state function because it only depends on the initial and final states of the system and not on the specific path taken during the reaction. This can be demonstrated by using Hess's Law, which states that the overall enthalpy change of a reaction is the same, regardless of the individual steps or reactions involved in the process. The enthalpy change only depends on the enthalpy values of the reactants and products and not on the intermediate steps of the reaction.

Enthalpy Change as an Extensive Property

Enthalpy change is an extensive property because it depends on the amount of reactants and products in the system. When the quantity of reactants changes, the overall enthalpy change of the reaction will also change. For example, if the amount of reactants in a reaction is doubled, the enthalpy change (\(ΔH\)) of the reaction will also double, making it directly proportional to the quantity of matter in the system. To summarize, the enthalpy change for a reaction is a state function because it depends only on the initial and final states of the system, and it is an extensive property because it depends on the quantity of matter in the system.