1. What is Enthalpy Change?

Enthalpy change (ΔH) is the heat energy transferred in a reaction at constant pressure. It represents the difference in enthalpy between products and reactants in a chemical reaction.

2. How Does the Formula Work?

The formula for enthalpy change at constant pressure is:

Where:

• \( \Delta H \) — Enthalpy change (J or kJ)
• \( q_p \) — Heat transferred at constant pressure (J or kJ)

Explanation: At constant pressure, the enthalpy change of a system equals the heat transferred to or from the system.

3. Importance of Enthalpy Change Calculation

Details: Calculating enthalpy change is essential for understanding energy changes in chemical reactions, determining whether reactions are exothermic or endothermic, and predicting reaction spontaneity.

4. Using the Calculator

Tips: Enter the heat transferred at constant pressure (q_p) in joules (J) or kilojoules (kJ). The calculator will return the enthalpy change (ΔH) in the same units.

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between ΔH and q?
A: ΔH is a state function (depends only on initial and final states), while q is a path function (depends on the process). At constant pressure, they are equal.

Q2: What does a negative ΔH value indicate?
A: A negative ΔH indicates an exothermic reaction where heat is released to the surroundings.

Q3: What does a positive ΔH value indicate?
A: A positive ΔH indicates an endothermic reaction where heat is absorbed from the surroundings.

Q4: When is this formula applicable?
A: This formula is specifically valid for processes occurring at constant pressure, which is common in open-container chemical reactions.

Q5: How does this relate to Gibbs free energy?
A: Enthalpy change is one component of the Gibbs free energy equation: ΔG = ΔH - TΔS, which determines reaction spontaneity.