Warm Up  What is the mass of an object with 1850 J moving at 6 m/s?  How many protons are in an element with an atomic mass of 51 and has 32 neutrons?  C 3 H 8 + O 2  CO 2 + H 2 O  Cu +2 Br -1  Mg +2 PO 4 -3  Iron (III) Nitride  Lithium Oxide

Chapter 7

 Chemical energy is the energy stored in the chemical bonds of a substance.  Chemical reactions involve the breaking of chemical bonds in the reactants and the formation of chemical bonds in the products.  Breaking bonds requires energy and the formation of chemical bonds releases energy

During a chemical reaction, energy is either released or absorbed  A chemical reaction that releases energy to its surroundings is called an exothermic reaction.  Propane reacts with Oxygen (Combustion)  C 3 H 8 + 5O 2  3CO 2 + 4H 2 O kJ (heat)  For this reaction to get started it has to overcome activation energy. Once that is done the reaction has enough energy to continue without additional energy input.

 A chemical reaction that absorbs energy from its surroundings is called an endothermic reaction.  In the reaction, more energy is required to break the bonds of the reactants than the released by the formation of the products.  Heat is absorbed therefore the energy term is found on the reactant  2HgO kJ  2Hg + O 2

Conservation of Energy  Exothermic-chemical energy of reactants is converted to heat plus chemical energy of the product.  Endothermic-heat plus chemical energy of the reactants is converted to chemical energy of the products.  No matter if the reaction is exothermic or endothermic, the total energy before the reaction and after the reaction is the same.

Write questions and answers 1. What happens to chemical bonds as a chemical reaction occurs? 2. How do chemical reactions involve energy? 3. Is the combustion of propane endothermic or exothermic? 4. When propane reacts with oxygen, does the surround area become warmer or cooler? 5. Is energy created during an exothermic reaction?

Answers 1. Chemical bonds are broken in reactant and formation of chemical bonds in product occurs. 2. Energy is either absorbed or released. 3. Exothermic-releases heat 4. Warmer 5. Yes exo-comes out of

Reaction Rate  A reaction rate is the rate at which reactants change into products over time.  Reaction rates tell you how fast a reaction is going.  Factors that affect reaction rates include temperature, surface area, concentration, stirring, and catalysts.

Catalysts  This is any substance that affects the reaction rate without being used up in the reaction.  A catalyst reduces the activation energy required to start a reaction.  It does this by providing a surface for the reactants to come together. It can also “invite” particles together so they will react.

Equilibrium  Equilibrium is a state in which the forward and reverse paths of a change take place at the same rate.  In a physical change, such as liquid water to water vapor, equilibrium is established when a reaction does not go to completion. Ex. Rate of evaporation = rate of condensation

 Chemical reactions can also be in equilibrium when a reaction does not go to completion.  This kind of reaction is called a reversible reaction.

Factors affecting chemical equilibrium  Temperature  Pressure  Concentration

 Contrast exothermic and endothermic reactions.  What factors can speed up a reaction?  Describe what equilibrium is.