1. Chemical Reactions The process by which a chemical change occurs Atoms are rearranged, and chemical bonds are broken and reformed One or more substances change to produce one or more different substances Types –Synthesis (creating) –Decomposition (separating) –Combustion (burning) –Displacement/Replacement/Acid-base (switching) Out of the four types of reactions, which would describe the chemical reaction taking place to the right?

2. Tips for knowing which type of reaction you have. Follow this series of questions. When you can answer "yes" to a question, then stop! 1) Does your reaction have oxygen as one of it's reactants and carbon dioxide and water as products? If yes, then it's a combustion reaction 2) Does your reaction have two (or more) chemicals combining to form one chemical? If yes, then it's a synthesis reaction 3) Does your reaction have one large molecule falling apart to make several small ones? If yes, then it's a decomposition reaction 4) Does your reaction have any molecules that contain only one element? If yes, then it's a single displacement reaction 5) Does your reaction have water as one of the products? If yes, then it's an acid-base reaction 6) If you haven't answered "yes" to any of the questions above, then you've got a double displacement reaction

3. Recap: Physical Change a change in shape, size, color, or state a change without a change in chemical composition a change that is reversible Examples tearing paper cutting your hair change in state Physical changes are NOT indicative of a chemical reaction

4. Recap: Chemical Change a change in which a substance becomes another substance having different properties a change that is not reversible using ordinary physical means Changes that usually cause, heat, sound, light, odor, fizzing/foaming, color changes You usually need more than one of the above characteristics to be considered a chemical change! Examples mixing vinegar & baking soda burning a piece of wood soured milk A chemical analysis is the only 100% way to know a chemical change has occurred.

5. Reaction Energy - All chemical reactions are accompanied by a change in energy. Some reactions release energy to their surroundings (usually in the form of heat) and are called exothermic. For example, sodium and chlorine react so violently that flames can be seen as the exothermic reaction gives off heat. - On the other hand, some reactions need to absorb heat from their surroundings to proceed. These reactions are called endothermic. A good example of an endothermic reaction is that which takes place inside of an instant '"cold pack." - Reactions that proceed immediately when two substances are mixed together (such as the reaction of sodium with chlorine) are called spontaneous reactions.

6. Chemical Equation Shorthand form for writing what reactants are used and what products are formed in a chemical reaction Sometimes shows whether energy is produced or absorbed Examples: 2H 2 + O 2  2H 2 O CH 4 + 2O 2  CO 2 + 2H 2 O C 6 H 12 O 6 + 6O2  6CO2 + 6H2O + energy

7. Components of a Chemical Equation 2H 2 + O 2 2H 2 O  (Reactants) (Products) (Yield) Chemical Formulas Chemical Formula Subscripts Coefficient Subscript

9. Describing Reactions Counting with moles Chemists need practical units for counting things. Because chemical reactions often involve large numbers of small particles, chemists use a counting unit called the mole to measure amounts of a substance. mole (mol)-an amount of a substance that contains approximately 6.02 x 10 23 particles of that substance (Avogadro’s number)

10. Describing Reactions Molar mass: The mass of one mole of a substance Molar mass: The mass of one mole of a substance The molar mass of an element is the same as its atomic mass expressed in grams. The molar mass of an element is the same as its atomic mass expressed in grams. Calculate the molar mass of a compound by adding up the atomic masses of its component atoms, and then expressing the sum in grams. Calculate the molar mass of a compound by adding up the atomic masses of its component atoms, and then expressing the sum in grams. Ex. (NaCl) 1 atom of Cl is 35 grams and one Na atom is 23 grams, so the molar mass of NaCl would equal to 58 grams; 1 mole of NaCl=58 grams Ex. (NaCl) 1 atom of Cl is 35 grams and one Na atom is 23 grams, so the molar mass of NaCl would equal to 58 grams; 1 mole of NaCl=58 grams

11. Calculations With Chemical Equations

12. Energy and Chemical Reactions Exothermic Reaction A chemical reaction in which energy is released. The products have greater bond energy than the reactants C 6 H 12 O 6 + 6O 2  6CO 2 + 6H 2 O + energy (respiration) Endothermic Reaction A chemical reaction in which energy is absorbed. The products have lower bond energies than the reactants 6CO 2 + 6H 2 O + energy  C 6 H 12 O 6 + 6O 2 (photosynthesis) Can you think of other reactions where energy is gained or released?

13. Rates of Chemical Reactions Temperature – a measure of the average kinetic energy of the particles in a sample of matter –Ex. Increasing the temperature when cooking Surface area – amount of material that comes into contact with the reactants –Ex. Cutting a potato into smaller pieces when cooking Concentration – amount of substance per volume –Ex. Turning the valve on a gas stove to increase the concentration of methane molecules Catalysts (enzymes) – organic substances that help speed up chemical reactions, but are not consumed in the reaction The rates at which chemical reactions can take place are based on the interaction (collisions) between the different particles. These rates can be impacted by the following:

14. Law of Conservation of Mass Proposed by Antoine Lavoisier In a chemical reaction, atoms are neither created nor destroyed All atoms present in the reactants are also present in the products Chemical equations must account for/show the conservation of mass  balancing equations H 2 + O 2 H 2 O  In its present form, does this chemical equation show a conservation of mass? How would you balance this equation to show the conservation of mass? 22 Reactants H  2 O  2 Products 4242 H  2 O  1 4242

15. Hints For Balancing Equations Count the atoms –List the number of atoms of each element to see which elements must be balanced Use a coefficient to add atoms to one side of the equation –Start with the reactant or product that has the greatest number of different elements Add a coefficient to another reactant or product –Make sure that the coefficients in your balanced equation are the smallest whole numbers possible (they should have no common factor other than one)