Provide an example of the enthalpy of formation of different compounds.

The enthalpy of formation is the energy change when one mole of a compound is formed from its constituent elements.

For example, the enthalpy of formation of water (H2O) is -285.8 kJ/mol. This means that when one mole of water is formed from its constituent elements (hydrogen and oxygen), 285.8 kJ of energy is released. The negative sign indicates that the reaction is exothermic, meaning that energy is released.

Another example is the enthalpy of formation of carbon dioxide (CO2), which is -393.5 kJ/mol. This means that when one mole of carbon dioxide is formed from its constituent elements (carbon and oxygen), 393.5 kJ of energy is released. Again, the negative sign indicates that the reaction is exothermic.

The enthalpy of formation can also be used to calculate the enthalpy change of a reaction. For example, if the enthalpy of formation of reactants and products are known, the enthalpy change of the reaction can be calculated using Hess's Law.

Overall, the enthalpy of formation is an important concept in thermodynamics and is used to understand the energy changes that occur during chemical reactions.