Enthalpy Calculator

Enthalpy calculator is used to find the change in enthalpy of any given reaction. Enthalpy refers to the total energy in a thermodynamic system. The article covers how to use the enthalpy calculator along with other useful information about enthalpy like how to calculate it manually, what it means, and more.

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How to use the enthalpy calculator?

This enthalpy calculator or enthalpy of reaction calculator is a simple online tool which only requires a few values. With this calculator, you don’t have to perform the calculation manually. You can also use this standard enthalpy calculator to check the accuracy of your answer.

  • First, enter the value of the Change in Internal Energy then choose the unit of measurement from the drop-down menu.
  • Then enter the value of the Change in Volume and choose the unit of measurement from the drop-down menu.
  • Finally, enter the value of the Pressure then choose the unit of measurement from the drop-down menu.
  • After entering all of the required values, the enthalpy calculator automatically generates the value of enthalpy for you.

How do I calculate enthalpy?

To understand this enthalpy change calculator better, let’s learn more about enthalpy. This refers to the measurement of the total energy of a given thermodynamic system. It comes in the form of either volume or heat multiplied by pressure. Enthalpy is a state function which means that it only depends on a system’s equilibrium state.

The change of enthalpy is the more intriguing quantity as this refers to the total energy exchanged within a given system. This is a simplified explanation of energy transfer which refers to the energy in the form of work or heat done in an expansion. Therefore, by definition, enthalpy is the total heat absorbed by a system along with the work done when it’s expanding:

H = Q + pV

Q refers to the internal energy
p refers to the pressure
V refers to the volume

But when it comes to calculating the change in enthalpy, you must consider both the initial and final state. Let’s assume that the pressure remains constant when the reaction occurs. In such a situation, the change in enthalpy is:

ΔH = (Q₂ – Q₁) + p * (V₂ – V₁) or ΔH = ΔQ + p * ΔV when simplified

V1 and Q1 refer to the volume and internal energy of the reaction of the product
V₂ and Q₂ refer to the volume and internal energy of the reactants
p refers to pressure which remains constant
ΔQ refers to the change in the internal energy
ΔV refers to the change in the volume
ΔH refers to the change in enthalpy.

How do you calculate standard enthalpy change?

You can use a delta h calculator, a heat of reaction calculator or a standard enthalpy calculator to calculate standard enthalpy change automatically. But if you want to perform a manual calculation, there are different methods for this and they depend on the date you have as well as the specific situation.

For most of the calculations, one significant piece of data you must use is Hess’ Law. However, if you already know the enthalpy of both the reactants and the products, the calculation becomes easier and simpler. For this situation, use this simple formula:

∆H = Hproducts − Hreactants

If you want to define enthalpy in the most precise way, it refers to the sum of internal energy “U” plus the product of the pressure (P) and the volume (V). In the form of an equation, it is:

H = U + PV

Therefore, a standard enthalpy change is:

∆H = ∆U + ∆P∆V

In this equation, the delta symbol or ∆ means “a change in.” Normally, you would hold the pressure as a constant value. Therefore, a better version of this equation is:

∆H = ∆U + P∆V

But for constant pressure, the standard enthalpy change simply refers to transferred heat:

∆H = q

If you get a positive value for q, this means that you have an endothermic reaction which means that it absorbs heat from the surroundings. If you get a negative value for q, this means that you have an exothermic reaction which means that it releases heat into the surroundings.

What is meant by the standard enthalpy of a reaction?

The standard enthalpy of a reaction which has a symbol of ΔHr⦵ refers to the enthalpy change that happens in a given system when matter gets transformed by a chemical reaction. Here, all of the products and reactants stay in the standard states.

For generic chemical reactions −vA A + −vB B + … → vP P + vQ Q … the standard enthalpy of reaction or ΔHr⦵ has a relation to the standard enthalpy of formation or ΔHf⦵ of products and reactants by an equation.

ΔHr⦵ = Σ vB ΔHf⦵ (B)

The equation doesn’t take into consideration the heat generated by mixing products and reactants or assuming the involved ideal solutions. In the equation, vB refers to the stoichiometric number of B.

The standard enthalpy of formation for a wide range of substances was already determined. It is the change of enthalpy which occurs when 1 mole of a substance forms from constituent elements while all the other substances remain in standard states.

You can compute the enthalpy change of a given reaction under any kind of conditions from this equation. That is as long as you have the standard enthalpy of formation of the products and the reactants.

In other words, the enthalpy change refers to how much heat gets evolved or absorbed when reactants transform at a given pressure and temperature into the products at exactly the same pressure and temperature.

What are the units of enthalpy?

As previously mentioned, enthalpy has the following equation:

H = U + PV

For pressure, use pascal as the standard unit of measurement. But you can also use kilogram per meter per second-squared or kg/[m_s^2]. For volume, use meter cubed or m3 as the standard unit of measurement.

When you multiply these units, you get kilogram meter-squared per second-squared or [kg*m^2]/[s^2] as a standard unit of measurement which is also called a joule. The internal energy also has this unit of measurement. Therefore, the unit of enthalpy is also joules.