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Enthalpy Calculator

Enthalpy Calculator

Calculate Enthalpy From:

Calculate From:

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


cn Coefficient

Reactant C


dn Coefficient

Product D


en Coefficient

Product E


fn Coefficient

Product F


An online enthalpy calculator is specially designed to calculate exact amount of enthalpy generated in a thermodynamic system. With the help of this tool, you can use either enthalpy formula or reaction scheme method to calculate changes in enthalpy.

So, before we move towards the brief explanation and calculation of enthalpy, let us discuss the basic phenomenon of enthalpy in the galaxy of Physics.

What is Enthalpy In Physics?

In the context of Physics, Enthalpy is referred to the change in heat. Addition of internal energy to the product of volume and pressure exerted on any thermodynamic system results in enthalpy. Whenever a system changes its state from solid to liquid (latent heat of fusion) or liquid to gas (latent heat of vaporization), it requires a sufficient intake of energy to produce a comprehensive change in enthalpy.

Hess’s law, Reaction Scheme and Enthalpy Formula are the most efficient ways to enumerate enthalpy of any thermodynamic system or chemical reaction. We will elaborate each of these ways in a brief manner to understand the proper concept for determining change in heat.

Did you know?

“delta h calculator helps you to determine almost absolute change in heat of any thermodynamic system.”

Examples of Enthalpy:

Real life examples of enthalpy change includes refrigerators and hand warmers. The reaction to the iron oxidation in hand warmers and vaporization of the refrigerants in compressor create a change in heat of the whole system at a constant pressure.
Standard Enthalpies of formation:
It is not possible to learn enthalpies of every substance. But for the sake of ease and time saving, we have arranged a table containing standard change in enthalpy of formation of substances that are mostly used in every chemical reaction.

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


Unit of Enthalpy:

According to System International (SI), the enthalpy 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 where;

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

The exact values of all the parameters mentioned in enthalpy change formula above can be determined using online free enthalpy calculator.

When we calculate change in enthalpy, we can find heat change at each step during the reaction by following the thumb rule of Reaction Scheme.

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

With the help of online enthalpy calculator, we can easily get heat changes at each step in the reaction and overall heat, ΔHf° within a few seconds.

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

How to Calculate Enthalpy Change?

We can easily calculate the enthalpy changes by taking into account each of ways mentioned above. Let us discuss the following examples to understand the concept.


Let’s suppose we have a thermodynamic system having internal energy of 5J. The pressure exerted on the system due to surroundings is 12Pa and the change in volume of the system is 39m3. What is the enthalpy of the system?


As we know that the enthalpy change formula is given as;

ΔH = ΔQ + p * ΔV

By putting the values of pressure, internal energy and change in volume, we can calculate change in enthalpy of the system as follows;

ΔH= 5J+12Pa*39m3

ΔH= 473J.

Example # 02:

Using reaction scheme, Determine change in enthalpy of the chemical reaction as follows:
2H2 + O2 → 2H2O?
Where standard enthapy of formation for each substance is given as follows:
H2=0, O2=0, H2O= -241.9


∑ΔH°f(reactants) = 2(0) + 0
= 0
∑ΔH°f(products) = 2(-241.9)
= -483.8
ΔH°reaction  = -483.8 – 0
= -483.8kJ
So, the overall change in enthalpy of reaction is -483.8kJ.

You can easily put these values in online enthalpy calculator to obtain desired result.

Let us discuss another example to determine heat of formation of the reaction using Hess’s law of heat summation.


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


We need to focus to find enthalpy of 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, we 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.

Example # 04:

You are given the enthalpy of a system as 7J. The internal energy of the system is approximately 4.1J and the volume is 11m3. Calculate the pressure exerted on the system due to its surroundings.


as we know that:

ΔH = ΔQ + p * ΔV

by making considerable change in enthalpy equation, we get;

p = ΔH – ΔQ / ΔV

p = 7 – 4.1 / 11

p = 0.263pa

However, an online Chemical Equation Balancer Calculator will provide you the balanced equation, equilibrium constant with chemical name and formula of all reactants and product of a chemical equation.

Enthalpy of Exothermic and Endothermic Reaction:

During an exothermic reaction, the overall energy of products remains less than that of reactants. That is why heat change is always negative as the heat is released in the surroundings.

In case of endothermic reaction, enthalpy is always positive because the products are higher in energy than the reactants and reaction absorbs energy from its surroundings.

How to Use Online Enthalpy Calculator?

We can calculate enthalpy change easily by using two different ways in online enthalpy change calculator. These ways are;

Enthalpy Formula:


  • First select ‘Enthalpy Formula’ option.
  • After doing so, select either ‘Internal energy & volume’ or ‘Change in internal energy & volume’.
  • Then put values against each parameter in tool and calculate.


The enthalpy calculator calculates:

  • The overall variation in heat and shows you with the step-by-step calculation corresponding to the given values and their units.

Reaction Scheme:


  • First, you need to select ’Reaction Scheme’ from drop down menu.
  • After doing so, you have to select either ‘2 reactants & products’ or ‘3 reactants & products’.
  • Then you have to put coefficients of each reactant as well as the amount of heat generated by each reactant.


  • You will obtain overall heat change.
  • Enthalpies of formation for individual reactants are calculated.


Is enthalpy a negative change in heat or positive change in heat?

The enthalpy of a reaction can either be positive or negative. Endothermic reactions result in positive enthalpy while exothermic reactions give rise to negative enthalpy.

What is the main cause of enthalpy?

Changes in heat during product formation in a chemical reaction is a major cause of enthalpy generation.

Can we calculate absolute enthalpy?

No, we can’t calculate the absolute enthalpy as reaction schemes take place at every temperature and thus change in heat occurs at all times which changes the enthalpy of the system continuously.

What is the relationship of enthalpy and pressure exerted on a system?

There exists a direct relationship among enthalpy and pressure. Increasing pressure on a system causes an increase in enthalpy of the system and vice versa.

What are the dimensions of enthalpy?

As enthalpy is a state function, it has the dimensions of energy and thus measured in ergs or jouls.


Enthalpy is a heat content of a thermodynamic system or chemical reaction. The enthalpy is never determined by its history and depends upon temperature, pressure and change in surroundings. When it comes to change in heat, boiler engineers typically use an enthalpy calculator online to decrease the uncertainty of calculations.


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.

From the source of Lumen Learning: Internal Energy and Enthalpy, Internal Energy Change at Constant Volume, Standard Enthalpy of Reaction, Enthalpy of Reaction at Constant Pressure, Exothermic and Endothermic Processes, Exothermic Reactions.