Topic: Names, Formulas, Equations, & Reactions Aim: What conservation laws are important in chemical reactions, & how do we count atoms in a compound? Do now: Write the formula for chromium III oxide HW:

Conservation of ENERGY During any phys or chem change, the total quantity of energy remains constant. Cannot be created or destroyed Transferred to different forms Ex. Lighting a match – chemical energy  light energy  thermal energy  chemical energy

Conservation of MASS Products of a chemical reaction have the same mass as the reactants Why equations must be balanced That’s MY idea! Antoine Laurent Lavoisier (1743-94)

Conservation of CHARGE The # of + or – charges on 1 side of the equation must equal the # of + or – charges on the other side All compounds must be electrically neutral, + balances –

Counting the # of Atoms in a Compound Subscript # to the right & below a symbol Tells # of atoms of that element If the subscript is written after a polyatomic ion in parentheses, the subscript applies to each element in the parentheses – multiply CO2 1 carbon, 2 oxygen Mg(OH)2 1 magnesium, 2 oxygen, 2 hydrogen

Counting the # of atoms in a Compound Coefficient Written in front of a formula Tells how many units of the formula are present & applies to the entire formula 4CO 4 carbon, 4 oxygen 4H2O 8 hydrogen (4x2), 4 oxygen

Counting the # of atoms in a Compound NO subscript or coefficient implies 1 CO  1 carbon, 1 oxygen BOTH a subscript & coefficient means multiply them 3CaSO4  3 calcium, 3 sulfur, 12 oxygen 4Mg(C2H3O2)2 4 magnesium, 16 carbon (2x2x4), 24 hydrogen (2x3x4), 16 oxygen (2x2x4)

Examples 2Na MgCl2 H2SO4 2H2O 4CaCl2 Na: 2 Mg: 1 Cl: 2 H: 2 S: 1 O: 4

Examples 2K3PO4 3Ca(NO3)2 Fe2(SO4)3 (NH4)2SO4 3Mg(C2H3O2)2

Examples 4Al(OH)3 CuSO4  5H2O 3MgSO4  7H2O 5Na2CO3 3Pb(SO4)2 2Ag3PO4 9C8H18 3Al2(SO4)3 4Fe3(PO4)2 2Mn(C2H3O2)7