What is Enthalpy?
Enthalpy (denoted as H) is a fundamental thermodynamic property that represents the total heat content of a system. It is defined as the sum of the system's internal energy plus the product of its pressure and volume. In most chemical reactions and physical processes occurring at constant pressure, the change in enthalpy (ΔH) is equal to the heat added to or lost from the system.
The Enthalpy Change Formula
The standard formula used in this enthalpy calculator is: ΔH = ΔU + PΔV.
Where:
- ΔH: Change in Enthalpy
- ΔU: Change in Internal Energy
- P: Constant Pressure
- ΔV: Change in Volume
How to Use the Enthalpy Calculator
Using this tool is straightforward. Simply follow these steps:
- Enter the Internal Energy change (ΔU). This represents the energy stored within the system's molecules.
- Provide the constant Pressure (P) under which the process occurs. Standard atmospheric pressure is approximately 101,325 Pascals.
- Enter the Change in Volume (ΔV). If the system expands, this value is positive; if it contracts, it is negative.
- Click "Calculate" to see the total enthalpy change and a detailed breakdown of the work done by the system.
Frequently Asked Questions
Is enthalpy the same as heat?
Under the specific condition of constant pressure, the change in enthalpy is numerically equal to the heat exchanged with the surroundings. However, they are conceptually different; enthalpy is a state function, while heat is a process variable.
What are the SI units for Enthalpy?
The standard unit for enthalpy in the International System of Units (SI) is the Joule (J). In larger chemical systems, it is frequently expressed in kilojoules (kJ) or kilojoules per mole (kJ/mol).
What does a negative enthalpy mean?
A negative ΔH indicates an exothermic reaction, meaning the system has released heat to its surroundings. Conversely, a positive ΔH indicates an endothermic reaction where the system absorbs heat.