Chemical Energy, Reaction Rates, and Chemical Equilibria Sections 7.3, 7.4, and 7.5

Energy Many types of energy –Kinetic –Potential –Light –Heat –**Chemical**

What is chemical energy? Chemical Energy- energy that is stored in chemical bonds –To break a bond requires energy –To make a bond releases energy

Energy In a chemical reaction, two things can be done with energy –It can be absorbed Endothermic reactions –It can be released Exothermic reactions

Endothermic reactions Absorb energy from surroundings More energy required to start reaction than is released in reaction 2HgO kJ  2 Hg + O 2 –kJ is a form of energy…energy is ADDED to the reaction

Exothermic reactions Release energy to surroundings More energy released in reaction than required to start it C 3 H 8 + 5O 2  3 CO 2 + 4H 2 O kJ –Energy is released as 2220kJ

Reaction time Not all reactions occur immediately Reaction rate –What is it? –What does it do? –Can anything change it?

Factors affecting reaction rate Temperature –The higher the temperature, the faster the reaction rate –Chocolate powder dissolves faster in hot water than cold milk

Factors affecting reaction rate Why does temperature affect reaction rate? –Higher temperatures make particles move faster –Faster movement = more collisions –More collisions = greater chance of reactants colliding to form products =faster reaction rate

Factors affecting reaction rate Surface area –The greater the surface area, the faster the reaction rate Loose sugar dissolves in water faster than sugar cubes

Factors affecting reaction rate Why does surface area affect reaction rate? –Greater surface areas mean more space for molecules to collide –More collisions means more reactions =faster reaction rate

Factors affecting reaction rate Stirring –The more a solution is stirred, the faster its reaction rate will be –Stirring lemonade powder helps it dissolve faster than letting it sit there

Factors affecting reaction rate Why does stirring affect reaction rate? –Stirring helps make particles move faster –Faster movement = more collisions –More collisions = greater chance of reactants colliding to form products =faster reaction rate

Factors affecting reaction rate Concentration –The higher the concentration of reactants, the faster its reaction rate will be –Adding more reactants will help the reaction

Factors affecting reaction rate Why does concentration affect reaction rate? –Increased concentration adds more particles –More particles= more collisions –More collisions = greater chance of reactants colliding to form products =faster reaction rate

Factors affecting reaction rate Catalysts –Special substances that help speed up reactions

Equilibrium What is it? What kinds are there? How does it affect reaction ? Who the heck is Le Chatlier?

Equilibrium Equilibrium is when forward and reverse paths take place at the same rate –Crowded restaurant: people can’t sit unless there’s an open table…leave same as enter

Equilibrium Physical equilibrium –Phase changes Closed water bottle has water vapor and liquid water in it Chemical equilibrium –A reversible reaction Shown by a double arrow…reaction occurs in both directions

Le Chatlier’s Principle “When a change is introduced to a system in equilibrium, the equilibrium shifts in the direction that relieves the change” –In other words, reactions will change based on what is happening to them Three factors/changes to worry about 1.Temperature 2.Pressure 3.Concentration

Equilibrium Temperature –Increase temperature: reaction will go to side opposite of heat –Decrease temperature: reaction will go to side with heat N H 2 ⇌ 2 NH kJ

Equilibrium Pressure –Increase pressure: reaction will go to side with less molecules –Decrease pressure: reaction will go to side with more molecules N H 2 ⇌ 2 NH kJ

Equilibrium Concentration –Increase reactants: reaction will go to side with the products –Increase products: reaction will go to side with the reactants N H 2 ⇌ 2 NH kJ