Chapter 7 Notes Chemical Changes – when a substance is changed at the molecular level and can not be changed back. Evidence Light produced Change in color Smoke New substance appear

Chapter 7 Chemical reactions can be either Endothermic or exothermic Endothermic reactions absorb energy (feel colder) Exothermic reactions give off energy (feel hot)

Chapter 7 Endothermic Reaction

Chapter 7 Exothermic Reactions

Chapter 7 Collision Theory (particle theory) In order for a reaction to occur the reactants must collide or come in contact with each other. Most collisions occur with gases Second with liquids Last with solids

Chapter 7 Writing chemical reactions Chemical formulas vs Chemical reactions Chemical Formula is when you have the formulas of the reactants and what products are produced. (Not Balanced) H2, O2, H2O Chemical Reaction is when the chemical formula is balanced 2H2 + O2  2H2O

Chapter 7 Types of Chemical Reactions Synthesis (Multiple things combine to make a more complex product) H2 + O2  H20 Decomposition (One thing breaking down into smaller parts) H20  H2 + O2 Single Replacement (A single substance replaces a bonded substance) 2Na + Zn(OH)2 Zn + 2NaOH Double Replacement (The positive ions on two bonded compounds switch places) FeO + 2HCl  H2O + FeCl2 Combustion (Burning of a hydrocarbon with O2) C3H8 + 5O2  4H2O + 3CO2 (Always get H2O and CO2)

Chapter 7 All Chemical Rxns are dependant on the activity series. Some things just don’t react with each other so mixing them won’t yield a reaction. Pg 259 Na(s) + HOH(l)  NaOH (aq) + H2(g) Mg (s) + H2O (l) No RXN

Chapter 7 The coefficients in a balanced reaction are representing the number of moles of each part needed to react to completion. 2H2 + O2  2H2O 2 moles of Hydrogen are required to react with 1 mole oxygen to make 2 moles water If you don’t have 2 moles of hydrogen but do have 1 mole of oxygen the reaction will stop once the hydrogen is used up and you will have extra oxygen that didn’t react.