Enter the sum of the change in enthalpy of the products (J) and the sum of the change in enthalpy of the reactants (J) into the calculator to determine the Standard Enthalpy.

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## Standard Enthalpy Formula

The following formula is used to calculate the Standard Enthalpy.

Es = dHp - dHr

- Where Es is the Standard Enthalpy (J)
- dHp is the sum of the change in enthalpy of the products (J)
- dHr is the sum of the change in enthalpy of the reactants (J)

To calculate standard enthalpy, subtract the sum of the change in enthalpy of the reactants from the change in enthalpy of the products.

## How to Calculate Standard Enthalpy?

The following two example problems outline how to calculate the Standard Enthalpy.

**Example Problem #1:**

- First, determine the sum of the change in enthalpy of the products (J). In this example, the sum of the change in enthalpy of the products (J) is given as 45.
- Next, determine the sum of the change in enthalpy of the reactants (J). For this problem, the sum of the change in enthalpy of the reactants (J) is given as 5.
- Finally, calculate the Standard Enthalpy using the equation above:

Es = dHp – dHr

Inserting the values from above and solving the equation:

Es =45 – 5 = 40 (J)

**Example Problem #2: **

Using the same process as above, first define the variables required by the formula. In this case, these values are provided as the following:

sum of the change in enthalpy of the products (J) = 70

sum of the change in enthalpy of the reactants (J) = 10

Entering these values gives:

Es = 70- 10 = 80 (J)