Energy Diagrams and Calculations--By Tina Zhao

Energy Diagrams:
















Important Terms:








Energy of reactants: Total potential energy of all reactants in the reaction




Energy of product: Total potential energy of all products in the reaction




Energy of the activated complex: potential energy of the "transition state" between reactants




and products.




Activation energy: The energy that must be added to get the reaction to progress




Enthalpy: It is the energy of products - energy of reaction 




There are some examples




（http://www.sciencegeek.net/Chemistry/taters/energydiagram.htm）


















Energy in the Equation






- The energy absorption or release can be placed directly in the equation.




Exothermic : Reactions have the energy term on the right hand side and a negative H




example: CH4 + 2O2 ------CO2 + 2H2O + 812KJ






Endothermic: Reaction have the energy term on the left hand side and a positive H




example: I2 + Br2 + 81.5KJ -------2IBr










Energy Calculations




- The value of H change of a reaction and is expressed in KJ per mole of one of the chemical.
- We ignore the negative in conversion calculation because we use words




example: Using the follow reaction, how many moles of CH4 are needed to produce 2100KJ 




of energy? 










CH4 + 2O2 ------- CO2 + 2H2O + 812 KJ








2100KJ x 1mole of CH4 / 812KJ = 2.6moles of CH4