Which of the following statements regarding enthalpy is false?

• A. The enthalpy change for a reaction is always positive.
• B. Enthalpy is a state function, meaning its change depends only on the initial and final states, not the path taken.
• C. Enthalpy changes are typically measured under constant pressure conditions.
• D. The enthalpy change for a reaction depends on the physical states of the reactants and products.

Answer: (A)

Verified step by step guidance

1. Understand the concept of enthalpy (H), which is a thermodynamic state function representing the heat content of a system at constant pressure.
2. Recall that enthalpy change (\$\Delta H\$) for a reaction can be either positive or negative, depending on whether the reaction is endothermic (absorbs heat) or exothermic (releases heat).
3. Analyze each statement: the statement claiming that the enthalpy change for a reaction is always positive contradicts the fact that exothermic reactions have negative enthalpy changes.
4. Recognize that enthalpy is indeed a state function, so its change depends only on the initial and final states, not on the path taken.
5. Note that enthalpy changes are typically measured under constant pressure, and that the physical states of reactants and products affect the enthalpy change because enthalpy values depend on phase and molecular interactions.