1. What is Enthalpy Change?

Enthalpy change (ΔH) is the heat energy change measured under conditions of constant pressure. It's a fundamental concept in thermodynamics that helps predict whether a chemical reaction will be exothermic (releases heat) or endothermic (absorbs heat).

2. How Does the Calculator Work?

The calculator uses the enthalpy change equation:

Where:

• \( \Delta H \) — Enthalpy change (kJ/mol)
• \( \sum \text{bonds broken} \) — Total energy required to break all bonds in reactants (kJ/mol)
• \( \sum \text{bonds formed} \) — Total energy released when new bonds form in products (kJ/mol)

Explanation: Breaking bonds requires energy (endothermic, positive sign), while forming bonds releases energy (exothermic, negative sign). The net change determines if the overall reaction is exothermic or endothermic.

3. Importance of Enthalpy Calculation

Details: Calculating enthalpy changes helps predict reaction feasibility, design chemical processes, and understand energy requirements in industrial applications.

4. Using the Calculator

Tips: Enter the total bond energies for broken and formed bonds in kJ/mol. Values must be positive numbers. The calculator will compute the enthalpy change.

5. Frequently Asked Questions (FAQ)

Q1: What does a negative ΔH value mean?
A: A negative ΔH indicates an exothermic reaction where more energy is released in bond formation than is required for bond breaking.

Q2: What does a positive ΔH value mean?
A: A positive ΔH indicates an endothermic reaction where more energy is required for bond breaking than is released in bond formation.

Q3: Where can I find bond energies?
A: Standard bond energies are available in chemistry reference tables. These are average values measured under standard conditions.

Q4: Are there limitations to this calculation?
A: Yes, bond energies are averages and don't account for molecular environment. For precise calculations, use Hess's Law with formation enthalpies.

Q5: How does this relate to Gibbs free energy?
A: While ΔH measures heat change, Gibbs free energy (ΔG = ΔH - TΔS) determines reaction spontaneity by also considering entropy (ΔS) and temperature (T).