Chemical Reactions New Substances produced by changing the way atoms are arranged Physical Changes ≠ Chemical Reaction Evidence Change in Color (rust) Temperature Change (endo/exo-thermic) Formation of a Gas Formation of a Solid (Precipitate)

Reactants: Substances Present @ Beginning Products: Substances Formed by the Reaction Yields: An “equal sign” in a chemical reaction meaning “produces”, “creates”, or “forms”… Na + Cl2  NaCl Reactants Yields Products Reactants Product

Reaction Classifications

Synthesis A + B  AB Mg + O2  MgO …Combining Elements… Product Reactants

…Separating Elements… Decomposition …Separating Elements… CD  C + D H20  H2 + O2 Reactants Product

…FIRE! (Needs Oxygen and produces CO2 )… Combustion …FIRE! (Needs Oxygen and produces CO2 )… EF + O2  H20 + CO2 + HEAT CH4 + O2  H20 + CO2 Reactants Product

…Switch out ONE element with another!... Single Replacement …Switch out ONE element with another!... GH + I  GI + H CuCl2 + Zn  ZnCl2 + Cu Reactants Product

…Switch Out Two Elements with Two Others!... Double Replacement …Switch Out Two Elements with Two Others!... JK + LM  JM + KL AgNO3 + HCl  AgCl + HNO3 (Stop Here) Reactants Product

Rate of Reaction Concentration Surface Area Temperature High Concentration = faster reaction The more particles – the more chance of collisions Surface Area More surfaces available to react = faster reaction Temperature Higher Temperatures = faster reaction Particles speed up or slow down…speeding up or slowing down the reaction…

Rate of Reaction (Cont’d) Catalyst Something that speeds up the rate of reaction without being affected itself. A good example is the way the platinum catalyst in a car’s catalytic converter works to change toxic carbon monoxide into less-toxic carbon dioxide. Inhibitor Something that slows down the rate of reaction without being affected itself.

The Law of Conservation of Mass Matter Can Neither Be Created Nor Destroyed Reactants and Products MUST be EQUAL!

Endothermic Reactions Endothermic reactions are reactions which take energy in from their surroundings. If a substance is undergoing an endothermic reaction would it’s surroundings get warmer or colder? It’s surroundings get colder. Endothermic reactions occur when the bonds of a substance are being broken.

Useful Endothermic Reactions When things dissolve they are undergoing an endothermic reaction. Cooking is an endothermic reaction. The food takes in the heat provided by the cooker. The chemicals of the food undergo a chemical reaction which makes them easier to digest. Cold packs for sports injuries rely on endothermic reactions. When you twist or shake the pack the chemicals in the pack start reacting. Because they undergo an endothermic reaction they take heat in from their surroundings. This makes the pack cold.

Exothermic Reactions Exothermic reactions give off heat. They occur when chemical bonds are formed. If substances are undergoing exothermic reactions will their surroundings get hotter or colder? The will get hotter.

Useful Exothermic Reactions Combustion: all combustion reactions give off heat. Neutralization reactions are exothermic. Hot Pad hand warmers When the hand warmer is shaken they chemicals inside undergo an exothermic reaction This releases the heat which helps to warm up your hand.