Chemical Formulas and Equations H 2 O NaCl CO 2 2H 2 + O 2 = 2H 2 O

Chemical Formulas Formulas that use chemical symbols and numbers to represent what makes up a substance. –NaCl – Sodium chloride (salt) –Na – Sodium, Cl - Chlorine –H 2 O – Dihydrogen monoxide (water) –H – Hydrogen, O - Oxygen –CO 2 – Carbon dioxide –C – Carbon, O - Oxygen

Subscripts Numbers written below and to the right of a chemical symbol in a formula. H 2 O – 2 Hydrogen, 1 Oxygen Tells how many atoms of an element are in each molecule. Only used if more than one atom is present.

C9H8O4C9H8O4 C = Carbon – 9 atoms H = Hydrogen – 8 atoms O = Oxygen – 4 atoms 3 elements 21 total atoms

H 2 SO 4 H = Hydrogen – 2 atoms S = Sulfur – 1 atom O = Oxygen – 4 atoms 3 elements 7 atoms

C 12 H 22 O 11 C = Carbon – 12 atoms H = Hydrogen – 22 atoms O = Oxygen – 11 atoms 3 elements 45 atoms

Coefficients # placed in front of a chemical symbol or formula Identifies the # of molecules of a substance –2H 2 O = 2 molecules of H 2 O –2FeO 3 = 2 molecules of FeO 3

Coefficients X Subscripts To determine the number of atoms using coefficients you multiply the coefficient with the subscript. 2H 2 O - 2 molecules of H 2 O = 4 Hydrogen atoms and 2 Oxygen atoms

2Fe 2 O 3 2 Molecules of Fe 2 O 3 = 2 X 2 = 4 Fe (iron) atoms 2 X 3 = 6 O (oxygen) atoms

Using Parentheses Multiply the subscript with each element in parentheses. Al 2 (SO 4 ) 3 Al = 2 atoms of Aluminum S = 3 X 1 = 3 atoms of Sulfur O = 4 X 3 = 12 atoms of Oxygen

(CH 3 ) 2 CHOH C = Carbon = 2x1 = 2+1 = 3 carbon atoms H = Hydrogen = 3x2 = 6+2 = 8 Hydrogen atoms O = Oxygen = only 1 Oxygen atom

Chemical Reactions Occurs when one or more substances change to produce one or more different substances. Atoms are rearranged to form a totally new substance with properties that are completely different Indicators of a chemical reaction –Gas formation –Solid formation – precipitate –Energy change – light or heat –Color change

Chemical Equations Uses chemical symbols and formulas to represent a chemical reaction. 2H 2 + O 2 → 2H 2 O Reactants Yield Products Sign

Chemical Reactions Elements are rearranged to form new substances in a chemical equation to show that a chemical reaction has occurred.

Chemical Equations Reactants –starting materials in a chemical reaction. Products –substances formed in a chemical reaction.

H 2 + O 2 → O 2 + H 2 Does this equation represent a chemical reaction? –Are the elements rearranged to form new substances? Reactants = H 2 and O 2 Products = H 2 and O 2 No! No new substance has been formed.

C 12 H 22 O 11 + H 2 O → H 2 O + C 12 H 22 O 11 Does this equation show the atoms rearranged to form NEW substances? Reactants = C 12 H 22 O 11 and H 2 O Products = C 12 H 22 O 11 and H 2 O No! No new substances have been formed.

Zn + 2HCl → ZnCl 2 + H 2 Does this equation show elements rearranged to form new substances? Reactants = Zn and 2HCl Products = ZnCl 2 and H 2 Yes! – New substances are formed.

Law of Conservation of Mass The mass of atoms and molecules is neither created or destroyed in chemical reactions. –The # of atoms for each element in the reactants must equal the # of atoms for each element in the products in a chemical reaction. –Chemical Equations must be balanced.

Chemical Equations Must Be Balanced! Law of Conservation of Mass The # of atoms in the reactants must equal the # of atoms in the products for each element

CH 4 + O 2 → H 2 O + CO 2 Reactants Carbon = 1 Hydrogen = 4 Oxygen = 2 NOT BALANCED! Products Carbon = 1 Hydrogen = 2 Oxygen = 3

NaCl + AgNO 3 → NaNO 3 + AgCl Reactants → Products Na – 1Na - 1 Cl – 1Cl - 1 Ag – 1Ag - 1 N – 1N - 1O – 3 Is this equation balanced? YES

2H 2 + O 2 → 2H 2 O Is this equation balanced? Reactants → Products H = 4H = 4 O =2O = 2 Yes!