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 describes the heat absorbed or released during a chemical reaction or physical change.

2. How Does the Calculator Work?

The calculator uses the enthalpy change equation:

Where:

• \( \Delta H \) — Enthalpy change (J/mol)
• \( q \) — Heat energy (Joules)
• \( n \) — Amount of substance (moles)

Explanation: The equation calculates the enthalpy change per mole of substance by dividing the total heat energy by the number of moles involved in the process.

3. Importance of Enthalpy Change Calculation

Details: Calculating enthalpy change is essential for understanding reaction energetics, predicting whether reactions will be exothermic or endothermic, and designing chemical processes.

4. Using the Calculator

Tips: Enter heat energy in Joules and amount of substance in moles. Both values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between ΔH and q?
A: q is the total heat energy, while ΔH is the heat energy per mole of substance (molar enthalpy change).

Q2: What are typical units for enthalpy change?
A: The standard unit is kJ/mol, though J/mol is also commonly used (1 kJ = 1000 J).

Q3: How is heat (q) measured experimentally?
A: Typically using calorimetry, where temperature changes are measured and converted to heat using known heat capacities.

Q4: What does a negative ΔH value indicate?
A: A negative ΔH indicates an exothermic process (heat is released), while positive ΔH indicates endothermic (heat is absorbed).

Q5: Can this equation be used for phase changes?
A: Yes, it can calculate the enthalpy of fusion/vaporization if q is the heat absorbed during the phase change.