Thermochemical Equations. Thermochemical equations are balanced chemical equations that include the physical states of all reactants and products and the energy change. 2H 2 O(l) 2H 2 (g) + O 2 (g) ΔH = 572 kJ CH 4 (g) + 2O 2 (g) CO 2 (g) + 2H 2 O(g) ΔH = -802 kJ. Phase Changes.
-- carried out under standard conditions which are one atmospheric pressure (1 atm) and 298K (250C)
- C6H1206(s) + 6O2(g)6CO2(g)+6H2O(l)
-- think of water vaporizing from your skin after you take a hot shower. Your skin provides the heat needed to vaporize the water and as the water absorbs the heat you feel cool (shiver)
ΔHvap = -ΔHcond (condensation)
--think of ice in a drink. The drink cools as it provides the heat for the ice to melt
ΔHfus= - ΔHsolid (solidification—freezing)
??What do you notice about the magnitude of the molar enthalpy of vaporization versus the molar enthalpy of fusion?
The molar enthalpy of vaporization for a substance is much larger than the molar enthalpy of fusion for the same substance. It takes much more energy to change a substance from a liquid to a gas than it does to change a solid to a liquid.