The enthalpy change (ΔH) in a chemical reaction can be calculated using the energy diagram (reaction coordinate diagram), where it represents the difference in energy between the reactants and products. The formula to calculate the enthalpy change is:
\[ \Delta H = H_{\text{products}} - H_{\text{reactants}} \]
Where:
- \( H_{\text{products}} \) is the total enthalpy of the products
- \( H_{\text{reactants}} \) is the total enthalpy of the reactants
Example:
Let's consider a hypothetical reaction represented by a simple energy diagram:
- Reactants: 50 kJ
- Products: 100 kJ
To calculate the enthalpy change:
-
Identify the enthalpy of the reactants: \[ H_{\text{reactants}} = 50 \text{ kJ} \]
-
Identify the enthalpy of the products: \[ H_{\text{products}} = 100 \text{ kJ} \]
-
Plug these values into the formula: \[ \Delta H = H_{\text{products}} - H_{\text{reactants}} = 100 \text{ kJ} - 50 \text{ kJ} = 50 \text{ kJ} \]
Result:
In this example, the enthalpy change for the reaction is \( \Delta H = 50 \text{ kJ} \). This indicates that the reaction is endothermic, meaning it absorbs energy from the surroundings.
If the products had lower energy than the reactants (for example, if the products were at 30 kJ), then:
\[ \Delta H = 30 \text{ kJ} - 50 \text{ kJ} = -20 \text{ kJ} \]
This would indicate that the reaction is exothermic, releasing energy.