Chemical Reactions

I. Formulas a)Chemical Formula: represents the type and number of element(s) in a chemical compound. The type of element is represented by its chemical symbol. The number of atoms of the element in the compound is represented by its subscript. Li 3 PO 4 Lithium = Li Phosphorus = P Oxygen = O 3 atoms 1 atoms 4 atoms NOTE: Subscripts are the numbers found to the lower right of a given chemical symbol. If a subscript is not present assume that it is a number one.

Types of Formulas 1.Molecular Formulas Represents the type and number of elements in a covalent compound. The subscripts do not need to be reduced in a molecular formula. Ex: C 2 H 4 Ethene C 6 H 12 O 6 Glucose C 6 H 12 O 6 Glucose

2. Empirical Formulas Represents the lowest whole number ratio of atoms in a compound. For ionic compounds, the formula is always empirical. This is due to the fact that one must reduce the subscripts in an ionic compound to the lowest whole number ratio. Ex: Calcium Sulfide Ca S Ca +2 S - 2 Ca 2 S 2 Crisscross Method Disregard the signs. Ca S Reduce

For covalent compounds (molecules), reducing its molecular formula to an empirical formula only shows the ratio of elements within the compound. Ex: C 6 H 12 O 6 Molecular Formula C 1 H 2 O 1 Empirical Formula Ratio: C:H:O = 1:2:1

H2OH2OH2OH2O Molecular and Empirical Formula

II. Chemical Equations A reaction indicates the concentration of reactants that are needed to get a product. The reactions must be balanced to establish ratios. Example: 2 Na + Cl 2  2 NaCl This reaction tells us that by mixing 2 moles of sodium atoms with 1 mole of chlorine molecules we will get 2 moles of sodium chloride What if we wanted 4 moles of NaCl? 10 moles? 50 moles?

III. Types of Chemical Reactions a) Synthesis: a reaction in which 2 or more chemicals combine to make one. * b) Decomposition: a reaction in which a single chemical compound breaks down into several elements or simpler compounds. A + B ---> AB 8 Fe + S 8 ---> 8 FeS AB ---> A + B 2 H 2 O ---> 2 H 2 + O 2

c) Single Replacement Reaction : a reaction in which an unreacted element replaces another that is already found within a compound. d) Double Replacement Reaction: a reaction in which the component species in one binary or ternary compound bind to the component species in another binary or ternary compound. A + BC ---> AC + B Mg + 2 H 2 O ---> Mg(OH) 2 + H 2 AB + CD ---> AD + CB Pb(NO 3 ) KI ---> PbI KNO 3

e) Combustion Reaction: an exothermic reaction in which an organic compound combines with gaseous oxygen to produce carbon dioxide and water as the main products. C 10 H O 2 ---> 10 CO H 2 O

IV. Evidence of Chemical Reactions There are several ways to determine if a reaction is CHEMICAL. the release (exothermic) or gain (endothermic) of energy. the formation of an insoluble precipitate. the evolution or formation of a gaseous product. a permanent color change.

V. Balancing Equations To abide by the Law of Conservation of Matter and Energy, the number of atoms within the reactants of a chemical equation must be equal to the number of atoms found within the products. a) Chemical Equation: - Indicates the concentration (moles) of reactants needed to form products with a specific concentration (# of moles). 1C 1 H 4 (g) + 2O 2 (g) → 1C 1 O 2 (g) + 2H 2 O 1 (g) THE NUMBERS IN RED ARE CALLED COEFFICIENTS. THEY INDICATE THE NUMBER OF MOLES OF THE CHEMICALS. COEFFICIENTS CAN BE USED TO ESTABLISH MOLE RATIOS. THE NUMBERS IN BLUE ARE CALLED SUBSCRIPTS. THEY INDICATE THE NUMBER OF ATOMS FOUND WITHIN THE COMPOUND. Reactants Products

b) Balancing Equations The combustion of propane (C 3 H 8 ) in the presence of molecular oxygen yields carbon dioxide and water vapor. 1. Write out the formulas for all chemicals involved in the reaction Propane C 3 H 8 Molecular Oxygen O 2 Carbon Dioxide CO 2 Water H 2 O 2.Arrange the reactants on the left side and the products on the right side of the yield sign __C 3 H 8 (g) + __O 2 (g) → __CO 2 (g) + __H 2 O (g) Reactants Products

3. Create a checklist of the types and amounts of atoms present in the reactants and products __C 3 H 8 (g) + __O 2 (g) → __CO 2 (g) + __H 2 O (g) CHOCHO Manipulate the coefficient to balance the # of atoms in the reactants and products. 3 X 3 X 7 4 X 8 X X 1