Chemical Reactions

Chemical Reactions are all around us

Describing Chemical Reactions chemical change - rearrangement of atoms to form a new substance Has new chemical and physical properties

Evidences of a Chemical Reaction Produce a gas Produce a solid (precipitate) Color change Odor change Temperature change Exothermic Endothermic Give off heat/light Produce sound

Chemical Reaction vs. Physical Change To prove a chemical change took place, you have to do a chemical analysis Properties of a new substance must differ from the original substance

made + steps  stampedes Analogy! Physical change is like printing a word in a different font, it’s the same word just looks different! stampedes  stampedes Chemical change is like scrambling letters to form new words made + steps  stampedes

Remember… All changes of state: Solid Liquid  Gas Are Physical Evaporation Condensation Melting Freezing Are Physical Changes!

Physical or Chemical Change?

Physical or Chemical Change?

Physical or Chemical Change?

Physical or Chemical Change?

Physical or Chemical Change?

Physical or Chemical Change?

Physical or Chemical Change?

Physical or Chemical Change? Rotten Egg

Physical or Chemical Change?

Physical or Chemical Change?

Physical or Chemical Change?

Physical or Chemical Change?

Physical or Chemical Change?

What causes Chemical Reactions?

Reaction and Energy Changes Chemical Reactions either RELEASE or ABSORB energy.

Release Energy Example: Natural Gas Methane + Oxygen  Carbon Dioxide + Water + ENERGY

Absorb Energy Example: Photosynthesis Carbon Dioxide + Water + ENERGY  Oxygen + Glucose

Chemical Equations Equations are used to represent chemical reactions Reactants – starting substances Products – new substances Reactants Product

Chemical Equations Arrow always points to the product Hydrogen + Oxygen Water Mercury Oxide Liquid Mercury + Oxygen Sodium Chloride Sodium + Chlorine

Word Equations – uses names Names of the reactants separated by a + Arrow separates reactants from products Names of products separated by a + Example: Hydrogen + Oxygen Water

Formula Equations – uses symbols Symbol of the reactants separated by a + Arrow separates reactants from products Symbol of the products separated by a + Example: H₂ + O₂ H₂O

Writing word and formula equations: Mercury oxide is heated to form liquid mercury and oxygen Word = Formula =

Common symbols in equations → : produces or forms + : plus (s) : solid (l) : liquid (g) : gas (aq) : aqueous - dissolved in water

Add the symbols Hydrogen + Oxygen Water Mercury Oxide Mercury + Oxygen Sodium Chloride Sodium + Chlorine

Common symbols in equations Reversible 1803 a scientist observed the formation of sodium carbonate crystals at the edge of a salt lake 2NaCl + CaCO3 → Na2CO3 + CaCl2. He recognized this as the reverse of the familiar reaction Na2CO3 + CaCl2→ 2NaCl + CaCO3. He reasoned that the excess of salt in the lake helped push the "reverse" reaction towards the formation of sodium carbonate

Common symbols in equations KI ______ The element symbol above the arrow indicates a catalyst. A catalyst is something that speeds up the reaction but is not changed during the reaction, so it goes above the arrow.

Review writing ionic compounds Magnesium Nitride Iron (III) Oxide Sodium Sulfide Copper (II) Chloride

Seven diatomic elements: Hydrogen (H2) Nitrogen (N2) Oxygen (O2) Fluorine (F2) Chlorine (Cl2) Iodine (I2) Bromine (Br2) Write these on back of periodic table!

Common Polyatomic Ions Write these down on the backs of your periodic tables

Writing polyatomic compounds Aluminum Hydroxide Mercury (II) Phosphate Aluminum Sulfate Copper (II) Bromide Lead (II) Chlorite Silver Cyanide Ammonium Oxide