Standard Enthalpies of Formation (ΔH°f)
quantities of energy associated with the formation of 1 mole of a
substance from its elements in their standard states (SATP- 25°C and
100kPa)
*The units for ΔH°f are always kJ/mol because the values are always
given for 1 mole
Writing formation equations:
1.
Write one mole of product in the state indicated in the question
2.
Write the reactant ELEMENTS in their standard states (as seen on
the periodic table)
3.
Balance the equation to yield one mole of the product
Example:
Write the equation for the formation of liquid ethanol
Now you try:
Write an equation for the formation of solid calcium carbonate
Using ΔH°f to find ΔH
(examples)
What is the thermochemical equation for the reaction of lime (calcium
oxide) and water. Use ΔH°f values to calculate. (p.s. you can find these
on p799)
Example: #2
What is the MOLAR enthalpy of combustion of methane fuel? (a gas)