Feb 21 - Enthalpy Calculations

H : Energy change in the reaction. Units - kJ/mole

Eg.  CH₄ + 2O₂  -->  CO₂ + 2H₂O  + 812kJ

H can be expressed as:

-812kJ/1mole CH₄ or -812kJ/2mole O₂ = -406kJ/1mole O₂

-812kJ/1mole CO₂ or -812kJ/2mole H₂O = -406kJ/1mole H₂O

Ex. calculate the energy released when 0.35 moles of  H₂O is produced

0.35 moles H₂O * (-406kJ/1mole H₂O) = -142.1kJ

                             2Sig Fig                    = -140kJ

Ex. How many moles of CH₄ are needed to produce 2100kJ of energy?

2100kJ * (1mole CH₄/-812kJ) = -2.586

                                                = -2.6

                                                is  2.6 since mole cannot be negative

Link to Enthalpy Calculation : http://www.saskschools.ca/curr_content/chem30/modules/module3/lesson3/lesson3.htm