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Counting atoms Formulas • A formula tells which elements make up a compound. subscripts • Numbers that tell how many atoms of each element make up a compound. • H2O • No subscript means there is one atom of that element Formula Element H2SO4 Hydrogen Sulfur oxygen CO2 HCl H2O C6H12O6 Number of atoms Coefficients • Whole numbers in front of a chemical formula that tell how many molecules of the compound are present. • 4CaCO3 • You need to distribute the 4 to all parts of the formula Parentheses • Subscripts outside parentheses distribute to the elements inside the parentheses. • C7H5(NO2)3 • (TNT) Practice • C2H4O2 • 3H2O2 • (CH4)3CO4 Evidence of chemical reactions • • • • • 1. gas produced 2. A change in temperature 3. Light is produced 4. color change 5. precipitate forms Chemical Equation Notes • Tell chemists reactants, products, physical states and proportions of each substance. • Reactants →Products Word equations • Baking soda + Vinegar →Sodium acetate +Carbon dioxide bubbles Formulas • Shorthand for writing chemical equations. • CH3COOH + NaHCO3 -> H2O + NaOCOCH3 + CO2 Conservation of Mass • The number and kind of atoms must be equal for products and reactants. • Matter can not be created or destroyed • Chemical reactions need to be balanced.