Enter the change in internal energy (J), the change in pressure (Pa), and the change in volume (m^3) into the calculator to determine the Change in Enthalpy. 

Change in Enthalpy Formula

The following formula is used to calculate the Change in Enthalpy.

dH = dU + dP * dV
  • Where dH is the Change in Enthalpy (J)
  • dU is the change in internal energy (J) 
  • dP is the change in pressure (Pa) 
  • dV is the change in volume (m^3) 

To calculate the change in enthalpy, multiply the change in pressure by the change in volume, then add the change in internal energy.

How to Calculate Change in Enthalpy?

The following example problems outline how to calculate the Change in Enthalpy.

Example Problem #1

  1. First, determine the change in internal energy (J). In this example, the change in internal energy (J) is given as 100 .
  2. Next, determine the change in pressure (Pa). For this problem, the change in pressure (Pa) is given as  5 .
  3. Next, determine the change in volume (m^3). In this case, the change in volume (m^3) is found to be 4.
  4. Finally, calculate the Change in Enthalpy using the formula above: 

dH = dU + dP * dV

Inserting the values from above yields: 

dH = 100 + 5 * 4 = 120 (J)


What is enthalpy and why is it important in thermodynamics?

Enthalpy is a property of a thermodynamic system, often symbolized by H, which combines the system’s internal energy with the product of its pressure and volume. It’s a crucial concept in thermodynamics because it helps in understanding and calculating the heat exchange in processes at constant pressure, which is common in many practical applications such as chemical reactions and phase changes. Enthalpy changes provide insights into the energy efficiency and feasibility of such processes.

How does the change in enthalpy differ from the change in internal energy?

The change in internal energy of a system, denoted as ΔU, refers to the energy change due to temperature variations within the system, excluding any work done by or on the system. On the other hand, the change in enthalpy, ΔH, accounts for both the change in internal energy and the work done by the system expanding or contracting against its surroundings (PΔV). Therefore, while ΔU focuses on internal energy variations, ΔH provides a more comprehensive view of energy changes, including work done at constant pressure.

Can the change in enthalpy be negative, and what does that signify?

Yes, the change in enthalpy (ΔH) can be negative, indicating that a process is exothermic, meaning it releases heat to its surroundings. This is a common characteristic of many chemical reactions and physical processes where the system loses energy. Conversely, a positive ΔH signifies an endothermic process, where the system absorbs energy from its surroundings. The sign of ΔH is thus crucial for understanding the direction of heat flow and the energy dynamics of processes.