Class Notes: Chemical Reactions

I.Combination Reaction = two or more substances combine to form a single substance **reactants are usually 2 elements or 2 compounds: one of them water **product is a single compound General equation: R + S  RS

Rules for predicting the product: 1.Product is always a single compound: a.Ionic – use charges to write formula b.Molecular – (2 nonmetals) -Will be named for you

2. If reactants are non-metallic oxide + H 2 O  acid-just add the reactants Ex. SO 2 +H 2 O  H 2 SO 3 3. If reactants are metallic oxide + H 2 O  base (OH - )-the metallic hydroxide Ex. CaO +H 2 O  Ca(OH) 2

II. Decomposition Reaction = a single compound is broken down into 2 or more simpler products -it is difficult to predict products unless the reactant is a simple binary compound **reactant is a single compound General Equation: RS  R + S

III. Single-Replacement reaction = atoms of an element replace the atoms of an element in a compound **reactants: element & compound **Products: different element & different compound

General Equation: T + RS  TS + R (T & R = metals) OR U + RS  RU + S (U & S = non-metal halogens) **Reaction does not always proceed To predict the products, see the activity series

Activity Series of Metals: Higher metals will replace lower metals; never the reverse **Li to Na will replace H from acids and water **Mg to Pb will replace H from acids only Halogens: F 2 Cl 2 Br 2 I 2 ---Higher will replace lower

IV. Double-Replacement reaction = an exchange of 2 positive ions between 2 ionic compounds Positive ions = metals, H +, NH 4 + *reactants = 2 ionic compounds **Products = will be 2 different ionic compounds

General equation: RS + TU  TS + RU **Look for polyatomics -list metallic products first (positive ions) -be sure to cross over charges when creating new compounds

V. Combustion reaction = oxygen reacts with an organic compound to produce CO 2 + H 2 O & lots of energy **reactants = hydrocarbon (C x H y ) + O 2 **Products = CO 2 + H 2 O (when complete)

General Equation and balancing: C x H y + O 2  CO 2 + H 2 O *When one side is even, and the other is odd… **Double everything but O 2 and count again