Feb16, Exothermic and Endothermic

Exothermic- a reaction where it realeases energy to the surroundings
Endothermic- a reaction where it absorbs energy from the surroundings


-Molecules held together by chemical bonds
          -Add energy to break bonds
          -Give off energy to join together

Endothermic- reaction takes more energy to break bonds than it gives off to form bonds

Exothermic - reaction takes less energy to break bonds than it gives off to form bonds

Enthalpy which has a symbol H and a unit joules, is the heat contained in the system

Energy Diagrams

-Chart the potential energy of the chemicals as they change from reactants to products

-Reactants start with certain amount of energy. Energy is added to start the reaction and then nergy is released as reaction proceeds

-The relative amounts of energy determine if a reaction is endothermic or exothermic

Endothermic-





Exothermic-

1. Energy of reactans = total potential energy of all reactants in the reaction

2. Energy of products = total potential energy of all products in the reaction

3. Energy of the activated complex = potential energy of the "transition state" between reactants and products

4. Activation energy = the energy that must be added to get the reaction to progess (reactants to activated complex)

5. ΔH (change in enthalpy) = the change in potential energy during the reaction. It is the energy of products

 - energy of reactants

Energy in Equation

-Exothermic reactions have energy term on right hand side and a negative ΔH

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

                                                           (ΔH)

Endothermic reactions have the energy term on the left hand side and positive ΔH

Videos that's helpful and entertaining

Links that might help : http://www.emsb.qc.ca/laurenhill/science/exo.html