Created By : Rina Nayak

Reviewed By : Rajashekhar Valipishetty

Last Updated : Apr 27, 2023

enthalpy calculator can assist you in calculating a reaction's change in enthalpy. All you need to do is provide the inputs as per the formula and find the unknown parameter in no time.

What exactly is Enthalpy?

Enthalpy is defined in physics as the product of the internal energy and the pressure of a given thermodynamic system. It depicts the current state of the system. It is not a heat transfer metric. In a nutshell, enthalpy is a measurement of a system's energy. The letter "H" stands for enthalpy. As a result, the formula for calculating enthalpy is H = U + PV = Enthalpy

How to Calculate a Reaction's Enthalpy?

There are two modes on the enthalpy calculator. The enthalpy change can be calculated using the reaction scheme or the enthalpy formula. Suppose you choose the first option:

  • Take a look at the reaction chart at the top of the calculator. Is there a need for a third reactant/product (C or F)? If this is the case, select advanced mode.
  • In the Reactants section, fill in the blanks. You must enter the coefficient before the compound and then choose your substance from the drop-down list (which is alphabetically ordered). If you can't find the suitable one, choose Custom and enter the standard formation enthalpy in kJ/mol.
  • Apply the same logic to the products.
  • Check the reaction scheme below and then read the outcome. That's your reaction's standard enthalpy change of creation!
  • Check the standard enthalpy of the formation table (for your chosen c) as an option

If you want to use the enthalpy formula to determine the enthalpy change then follow the below process

  • Begin by calculating the volume change of your substance. Assume your liquid has increased in volume by 5 litres.
  • Determine the change in the substance's intrinsic energy. Let's say the energy of your substance rose by 2000 J.
  • Take note of the pressure in the area. We'll go with one atmosphere.
  • To calculate the change in enthalpy, plug all of these values into the equation ΔH = ΔQ + p * ΔV i.e. ΔH = 2000 J + 1 atm * 5 l = 2000 J + 101,325 Pa * 0.005 m³ = 2506.63 J
  • You may also use our enthalpy calculator's advanced mode to calculate the enthalpy depending on the starting and final internal energy and volume.

Is the reaction endothermic or exothermic?

Endothermic and exothermic reactions are the two primary types of thermodynamic reactions. Heat is absorbed from the environment in an endothermic reaction. An exothermic one emits heat into the environment.

Both of these reaction types result in changes in energy levels and, as a result, in enthalpy. All you need to remember for this calculator is that the change in enthalpy is positive if the process is endothermic because heat is acquired (absorbed from the surroundings).

The enthalpy change is adverse in an exothermic reaction because heat is lost (released to the surroundings).

Enthalpy Formula

By definition, enthalpy is the total of heat absorbed by a system and work done as it expands: Q + pV = H

Internal energy is denoted by Q, pressure is denoted by p, and volume is denoted by V.

However, you must consider two states when calculating the change in enthalpy: initial and final. We'll suppose that the pressure remains constant during the reaction. Then the enthalpy change is actually ΔH = (Q₂ - Q₁) + p * (V₂ - V₁) or put it in other way ΔH = ΔQ + p * ΔV


  • Q2 and V2 are the internal energy and volume of the reaction's products, respectively.
  • Q1 and V1 are the reactants' internal energy and volume, respectively
  • p — Pressure that is constant
  • Q — Internal energy change
  • V stands for volume change
  • H stands for enthalpy change

Standard Enthalpy of Formation Table and Definition

We can use the standard enthalpy of formation of a compound, abbreviated as H°f, to solve more specific problems. It's the change in enthalpy, H, that occurs when one mole of a substance is formed in its standard state, ° (pressure 105 Pa = 1 bar, temperature 25 °C = 298.15 K), from its pure elements, f.

For a reaction, the standard enthalpy of formation formula is as follows H°reaction = H°f(products) - H°f(reaction) (reactants)

  • H°reaction — The standard enthalpy change of formation in kJ.
  • H°f(products) is the sum of standard enthalpies of formation expressed in kJ/mol, and
  • H°f(reactants) is the sum of the standard enthalpies of the reactants' formation kJ/mol.

You may have noticed that H°f(products)ΔH°f(products) and H°f(reactants) have different functions than ∑ΔH°f(reactants) if you've been paying attention. This is because you must multiply them by the number of moles or the coefficient before the chemical in the reaction. We'll show you an example later that should clear everything out.

But first, you might wonder, "How can I figure out the normal enthalpy of production for each compound?" Using the standard enthalpy of the formation table is the easiest solution! As an example, consider the following:

ΔH°f (kJ/mol)

The state is indicated by the symbols in brackets: s - solid, l - liquid, g - gas, and aq - dissolved in water. Select the matching compound in the enthalpy calculator's drop-down list if you require the standard enthalpy of production for other compounds. All of the most common chemicals were included!

If you would like to learn more about the other chemical calculators that gives instant results, stay tuned to Chemistrycalculatorpro.Com

FAQ’s on Enthalpy Calculator

1. What is the formula for calculating H?

To find delta H, subtract the total of the reactant temperatures of formation from the heats of formation of the products: delta H = –110.53 kJ/mol – (–285.83 kJ/mol) = 175.3 kJ.

2. What is the formula for calculating molar enthalpy?

Molar enthalpy is equal to DH/n, where n is the number of moles of reactant. So we divide the properly measured mass by the molar mass to get moles. "C" stands for concentration, and "M" stands for moles per litre.

3. How does decomposition enthalpy work?

The enthalpy change during a reaction is equal to the enthalpy of the products minus the enthalpy of the reactants, according to this equation. The reaction's total enthalpy is –36 kilojoules, meaning that 1 mole of ammonium nitrate releases 36 kJ of heat during decomposition.

4. Is Hess's law correct?

The total enthalpy change of a procedure written as the sum of multiple sequential techniques is equal to the sum of the enthalpy changes of the individual steps. Because enthalpy is a part of the state, Hess' law holds.