Question

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

Short answer

The enthalpy change for a reaction, denoted by ΔH, is a state function because it depends only on the initial and final states of the system and not on the path taken to reach those states. It represents the difference in enthalpy between the products and reactants (ΔH = H_products - H_reactants). Moreover, enthalpy change is an extensive property as it depends on the amount of material involved in the reaction, meaning it increases proportionally with the quantity of reactants.

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. In other words, a state function does not depend on the process or the history of the system, only on its present condition.

Definition of Extensive Property

An extensive property is a property of a system that depends on the amount of material present in the system. It means that if the quantity of the system increases, the value of the extensive property will also increase proportionally.

Enthalpy Change as a State Function

Enthalpy (H) is a thermodynamic property that represents the total energy of a system, including its internal energy (U) and the energy associated with the pressure-volume work (PV): H = U + PV. The enthalpy change for a reaction, denoted by ΔH, is the difference in enthalpy between the final state (products) and the initial state (reactants), given by ΔH = H_products - H_reactants. Since enthalpy change depends only on the initial and final states of the system in a reaction and not on the path taken to reach those states, it is a state function.

Enthalpy Change as an Extensive Property

Enthalpy change is an extensive property because it depends on the amount of material involved in the reaction. If the quantity of reactants involved in a reaction increases, the amount of energy transferred as heat during the reaction (which is represented by the enthalpy change) will also increase proportionally. In summary, the enthalpy change for a reaction is a state function because it depends only on the initial and final states of the system and not on the path taken to reach those states. It is also an extensive property because it depends on the amount of material involved in the reaction.