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Enthalpy Calculator

Enthalpy Calculator

Enter the required parameters and the calculator will calculate the amount of enthalpy generated in the heating system, with the steps shown.


Calculate Enthalpy From:

Internal Energy & Volume:

Calculate From:

ΔH = ΔQ + p * ΔV
anA + bnB + cnC → dnD + enE + fnF

Internal Energy of Reactants


Internal Energy of Products


Volume of Reactants


Volume of Products


Change in Internal Energy


Change in Volume


Constant Pressure


an Coefficient

Reactant A


bn Coefficient

Reactant B



Reactant C


dn Coefficient

Product D



Product E


fn Coefficient

Product F



The enthalpy calculator is specially designed to calculate the exact amount of energy generated in an exothermic or endothermic reaction. 

What is Enthalpy in Physics?

“Enthalpy is the measure of the total energy released or absorbed in a  thermodynamic system”

Whenever a system changes its state from solid to liquid (the latent heat of fusion) or liquid to gas (the latent heat of vaporization), it requires a sufficient intake of energy to produce a comprehensive change in entropy.

Unit of Enthalpy:

According to System International (SI), the entropy is expressed in joule per kilogram or simply joule.

Enthalpy Change Equation:

At a constant temperature and pressure, the enthalpy equation for a system is given as follows:

ΔH = ΔQ + p * ΔV


  • ‘ΔH’ is the change in heat of a system
  • ‘ΔQ’ is the change in the internal energy of a system
  • ‘P’ is pressure on the system due to the surroundings
  • ‘ΔV’ is the change in the volume of the system

For a General Reaction:

anA + bnB + cnC → dnD + enE + fnF

the enthalpy equation is as follows;

“ΔH° of reaction = ∑ΔH°f(products) – ∑ΔH°f(reactants)”


  • an, bn, and cn are the coefficients of the reactants,
  • A, B, and C are reactants,
  • dn, and fn are coefficients of products formed,
  • D, E, and F are products.
  • ∑ΔH°f(products) is the change in heat during product formation,
  • ∑ΔH°f(reactants) is the change in heat of reactants

However, the Heat Specific Calculator will allow us to determine the specific heat, mass of substance, and initial and final energy of any substance.

Example of Enthalpy: 

Using Hess’s Law evaluate the enthalpy of formation, ΔHfo, of FeCl3(s) from changes in enthalpy of the following two-step process that occurs under standard state conditions:

Fe(s)+Cl2(g)⟶ FeCl2(s)ΔH°= -258.69kJ
FeCl2(s)+3/2Cl2(g)⟶ FeCl3(s)ΔH°=−47.7kJ


Need to focus on finding the enthalpy of the formation of FeCl3(s), which is equal to ΔH° for the reaction:
Fe(s)+5/2Cl2(g)⟶ FeCl3(s) ΔHfo=?
By looking at the reactions, see that the overall enthalpy ΔHfo for FeCl3(s) is equal to the sum of two reactions with known ΔH values.
Fe(s)+Cl2(g)⟶ FeCl2(s) ΔH°= -258.69kJ
FeCl2(s)+3/2Cl2(g)⟶ FeCl3(s) ΔH°= −47.7kJ

Fe(s)+5/2Cl2(g)⟶ FeCl3(s) ΔHfo= -306.39
The enthalpy of formation, ΔHf, of FeCl3(s) is −306.39 kJ/mol.

The enthalpy and the heat changes at each step in the reaction and overall heat, ΔHf° within a few seconds.

The Enthalpy Table:

Sr # . Name of Substance Symbolic Formula Standard Enthalpy of Formation ‘ΔH’
1. Potassium Chloride KCl(s) -435.9
2. Potassium Chlorate KClO3(s) -391.4
3. Sodium Chloride NaCl(s) -411.0
4. Sodium Hydroxide NaOH(s) -426.7
5. Zinc Sulphide ZnS(s) -202.9
6. Zinc Oxide ZnO(s) -348.0
7. Copper Sulphate CuSO4(s) -769.9
8. Copper Oxide CuO(s) -155.2
9. Calcium Dioxide Ca(OH)2(s) -986.6
10. Water H2O(l) -285.8
11. Chloroform CHCl3(l) -131.8
12. Carbon Dioxide CO2(g) -393.5
13. Hydrogen Sulphide H2S(g) -20.1
14. Ammonia NH3(g) -46.2
15. Sulphur Trioxide So3(g) -395.2
16. Hydrochloric Acid HCl(g) -92.3
17. Nitrogen Oxide NO(g) +90.4
18. Nitrogen Dioxide NO2(g) +33.9
19. Phosphorus Pentachloride PCl5(g) -398.9
20. Phosphorus Trichloride PCl3(g) -306.4
21. Sulphur Dioxide SO2(g) -296.1


From the source of Wikipedia: Characteristic functions, Physical interpretation, Relationship to heat, Heat of reaction, Specific enthalpy, Throttling, Compressors.

From the source of Libre Text: Enthalpy Change Accompanying a Change in State, Effect of Temperature on Enthalpy, The Enthalpy of Phase Transition.