Explain the difference between the enthalpies of formation of gaseous water and liquid water which are respectively, -242 and -286 kj/mol at 298 K.... Explain Please!
When gaseous H2O (vapor) condenses to a liquid, additional heat is released.
The enthalpy of formation is the change in enthalpy that occurs when one mole of a substance is formed from its constituent elements, with all reactants and products in their standard states. For water, the enthalpy of formation (ΔHf) can be calculated based on the enthalpies of formation of its constituent elements, hydrogen (H2) and oxygen (O2), and the balanced chemical equation for the formation of water.
The enthalpy of formation of gaseous water (-242 kJ/mol) refers to the enthalpy change when one mole of gaseous water is formed from hydrogen gas and oxygen gas at standard states (298 K and 1 atm). On the other hand, the enthalpy of formation of liquid water (-286 kJ/mol) refers to the enthalpy change when one mole of liquid water is formed from its constituent elements at standard states.
The difference in the enthalpies of formation between gaseous and liquid water can be explained by the difference in the physical state of the water molecules. In gaseous water, the molecules are in a vapor state, while in liquid water, the molecules are in a condensed state.
To calculate the enthalpy of formation of water, you need to consider the enthalpies of formation of hydrogen gas and oxygen gas, which are known values. Then, you can subtract the sum of the enthalpies of formation of the reactants (hydrogen and oxygen) from the enthalpy of formation of water. This will give you the enthalpy of formation of water.
It is important to note that the values of enthalpy of formation may vary with temperature and pressure. The values provided (-242 and -286 kJ/mol) are for water at 298 K, but these values may change at different temperatures or pressures.
In summary, the enthalpies of formation of gaseous and liquid water represent the energy change when one mole of water is formed from its constituent elements in different physical states. The enthalpy of formation can be calculated using known enthalpies of formation of the reactants and the balanced chemical equation.