1. What is Chemical Enthalpy?

Enthalpy (H) is a thermodynamic quantity equivalent to the total heat content of a system. It is equal to the internal energy of the system plus the product of pressure and volume. The enthalpy change (ΔH) of a reaction is the heat absorbed or released at constant pressure.

2. How Does the Calculator Work?

The calculator uses the enthalpy equation:

Where:

• \( \Delta H \) — Enthalpy change (kJ)
• \( \Delta U \) — Internal energy change (kJ)
• \( P \) — Pressure (Pa)
• \( \Delta V \) — Volume change (m³)

Explanation: The equation accounts for both the change in internal energy and the work done by the system at constant pressure.

3. Importance of Enthalpy Calculation

Details: Enthalpy calculations are crucial in thermodynamics for determining heat flow in chemical reactions, phase changes, and other physical processes at constant pressure.

4. Using the Calculator

Tips: Enter internal energy change in kJ, pressure in Pascals (Pa), and volume change in cubic meters (m³). The calculator will compute the enthalpy change in kJ.

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between ΔH and ΔU?
A: ΔH includes both internal energy change and pressure-volume work, while ΔU is just internal energy change.

Q2: When is ΔH approximately equal to ΔU?
A: For reactions involving only liquids or solids where ΔV is negligible, or in constant volume conditions.

Q3: Why is enthalpy important in chemistry?
A: It helps predict whether reactions will release or absorb heat and is used to calculate reaction spontaneity.

Q4: What are typical units for enthalpy?
A: kJ/mol for molar enthalpy, or kJ for total enthalpy change.

Q5: How does this relate to Hess's Law?
A: Hess's Law uses enthalpy changes of individual steps to calculate the overall enthalpy change of a reaction.