Chemical vs. Physical Changes Physical Change –No new compounds are formed –Ex. Cutting, ripping, dissolving, phase changes…

Chemical vs. Physical Changes Chemical Change –Bonds are broken and the atoms in compounds are rearranged –New Compounds are created –Are the result of chemical reactions

Chemical Reactions Evidence –Bubbling, Cloudy solution, Temperature Change, Color Change, Smoke, Light, Heat Reactants: what you start with Products: what you end with

Can be written as a sentence or an equation : Methane reacts with oxygen to form carbon dioxide and water. or CH 4 + O 2  CO 2 + H 2 O (REACTANTS)  (PRODUCTS)

Law of Conservation of Mass During a chemical reaction, atoms CANNOT be created nor destroyed, only rearranged!

Law of Conservation of Mass The mass of the reactants must equal the mass of the products. This is only easily observable in a closed system – one where the products (especially gases) cannot escape to the environment. In an open system – one where reactants and products can come and go – this law is difficult to observe.

Law of Conservation of Mass In other words, the number of atoms of each element in the reactants must equal the number of atoms in the products. CHEMICAL EQUATIONS MUST BE BALANCED!!!

How to Balance Equations 1.Count the number of atoms on each side of the reaction. 2.Put a coefficient in front of one molecule that has too few atoms of an element. 3.Count the number of atoms again. 4.If all are equal—YOU ARE DONE! If not—REPEAT steps 2-3 until they are!

CH 4 + O 2  CO 2 + H 2 O Count the number of atoms: Reactants: C – 1 H – 4 O – 2 NOT BALANCED!!!!!!! Products: C – 1 H – 2 O – = 3

CH 4 + O 2  CO 2 + 2H 2 O Count the number of atoms: Reactants: C – 1 H – 4 O – 2 NOT BALANCED!!!!!!! Products: C – 1 H – 4 O – = 4

CH 4 + 2O 2  CO 2 + 2H 2 O Put in coefficients: Reactants: C – 1 H – 4 O – 2 * 2 = 4 BALANCED!!!!!!!!!! Products: C – 1 H – 2 * 2 = 4 O – = 4

Formula Mass The total mass of a molecule of a compound

Formula Mass Avogadro’s number, aka the mole, is equal to 6.02 x Just like a dozen means 12, the word “mole” represents a number. Avogadro’s number, allows us to convert atomic mass units to grams.

Types of Reactions Addition/Synthesis: two or more substances combine to form a single compound A + B  AB Shortcut – only one product

Types of Reactions Decomposition: one compound breaks apart to form two or more products AB  A + B Shortcut – only one reactant

Types of Reactions Single-Replacement (Displacement): an element replaces another element in a compound A +BX  AX + B Shortcut - one element & one compound on both sides

Types of Reactions Double-Replacement (Displacement): two elements in different compounds switch places AX + BY  BX + AY Shortcut - Two compounds with elements switching places in each

AB + O 2  CO 2 + H 2 O Combustion: a compound containing carbon and hydrogen combines with oxygen to form carbon dioxide and water By Bailey Harp

Types of Reactions Exothermic: reactions that give energy off to their surroundings. See a flame or feel heat (hand warmers, MREs) Endothermic: reactions that absorb energy from their surroundings. Feel cold (instant ice packs)