Free Enthalpy Calculator is helpful to find the chnage in enthalpy of a reaction. We have two simple methods to calculate the enthalpy change like reaction scheme and enthalpy formula. Students have to select one method to calculate the enthalpy, enter the required input details and hit the calculate button to avail change in enthalpy value easily.

Below-listed are the useful steps to compute the enthalpy change of a chemical reaction using either enthalpy formula or using the chemical reaction scheme. Follow these steps for obtaining the result easily.

**Using Enthalpy Formula:**- Obtain the internal energy, volume of the reactants, products and pressure.
- Subtract the products volume from the reactants volume and multiply it by the constant pressure.
- Subtract the internal energy of the products from the reactants.
- Add the result in step 2 with the step 3 to get the chnage in enthalpy.
**Using Reaction Scheme**- Get any balanced chemical reaction.
- Find the standard enthapies of the each of the substance in the reaction.
- Find the sum of enthapies of reactants and sum of products enthapies.
- Subtract total enthapies products from the reactants to check the change in enthalpy.

Enthalpy measures the total amount of energy of a thermodynamics system which is in the form of heat or volume multiplied by the constant pressure.

The formula to calculate the enthalpy is along the lines:

**H = Q + pV**

Where,

Q is the internal energy

p is the vpressure

V is the volume

H is the enthalpy.

To calculate the change in enthapy, you need initial and final values with constant pressure. The formula for enthalpy change is ΔH = (Q₂ - Q₁) + p * (V₂ - V₁) or

**ΔH = ΔQ + p * ΔV**

Where,

Q₁, Q₂ are the internal energies of the products and reactants.

V₁, V₂ are the volume of the products and reactants

p is the pressure

ΔH is change in enthalpy

ΔQ is change in inyternal energy

ΔV is the change in volume

**Standard Enthalpy of Formation**

It is another method used to compute the enthalpy change. The standard enthalpy of formation of a compound is ΔH°_{f}. It is nothing but the change in enthalpy for forming one mole of substance in the standard state.

The standard enthalpy of formation formula is given as

**ΔH° _{reaction} = ∑ΔH°_{f(products)} - ∑ΔH°_{f(reactants)}**

Where,

∑ΔH°_{f(reactants)} is the sum of the standard enthalpes of the reactants.

∑ΔH°_{f(products)} is the sum of the standard enthalpies of the products

ΔH°_{reaction}is the enthalpy change

The standard enthalpy of each chemical substance is collected from the standard enthalpy of formation table mentioned below:

Substance | Change in Enthalpy in kJ/mol |
---|---|

O₂(g) | 0 |

SO₂(g) | −296.83 |

SO₃(g) | −395.72 |

H₂O(l) | −285.8 |

Cu₂O(s) | −168.6 |

Mg²⁺(aq) | -466.85 |

**Example**

**Question: Calculate the change in enthalpy for 2H _{2} + O_{2} → 2H_{2}O?**

**Solution:**

Given chemical reaction is 2H_{2} + O_{2} → 2H_{2}O

The standard enthalpy of formation of substances is here.

H_{2} = 0, O_{2} = 0, H_{2}O = −285.8

Change in enthalpy formula is ΔH°_{reaction} = ∑ΔH°_{f(products)} - ∑ΔH°_{f(reactants)}

∑ΔH°_{f(reactants) = 2(0) + 0 = 0}

∑ΔH°_{f(products)} = 2(-285.8) = -571.7

ΔH°_{reaction} = -517.7 - 0 = -517.7

Therefore, change in enthalpy of the reaction is -517.7 kJ.

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** 1. What is meant by Enthalpy?**

Enthalpy is the measurement of energy in a thermodynamic system. The amount of enthalpy is equal to the sum of heat absorbed by the system and work done.

**2. What is the Enthalpy Formula?**

The formula to calculate enthalpy is H = Q + pV.

The formula to find change in enthalpy is ΔH = ΔQ + p * ΔV.

**3. What is enthalpy of chemical reaction?**

The bonds between atoms can form or dissolve during chemical reaction to either absorb or release heat energy. The heat either absorbed or emitted under the constant pressure from a device is called the enthalpy. The reaction enthalpy is the change in enthalpy arising from a chemical reaction.

**4. Why enthalpy is useful?**

Enthalpy is important because it tells about the amount of heat energy in a system. An enthalpy shift shows how much enthalpy was lost or gained in terms of a chemical reaction. In simple words, enthalpy means system heat energy.