Chemical Equations

A chemical equation is a form of shorthand which gives an outline of the progress of a chemical reaction: 2 H 2 O → 2 H 2 + O 2 REACTANT PRODUCT the arrow can be interpreted as “reacts to produce”

Conservation of Mass “matter is neither lost nor gained during a chemical reaction”. in other words, there is no magic; the number any type of atoms on the reactant side must equal the number and type of atoms on the product side. it is the reason we balance chemical equations.

Other Information Subscripts are often used to indicate the phase of each component of a chemical reaction: –(s) - solid –(l) - liquid –(g) - gas –(aq) -aqueous (meaning that the compound is dissolved in water.) –(ppt) -precipitate (meaning that the reaction produces a solid which falls out of solution.)

Types of Chemical Reactions 1)Synthesis two or more simple substances combine to form a more complex compound element + element → compound S 8 (s) + 8 H 2 (g) → 8 H 2 S (g) N 2 (g) + 3 H 2 (g) → 2 NH 3 (g)

2)Decomposition One substance breaks down to form two or more simpler substances. compound → element + element 2 NO 3 (g) → N 2 (g) + 3 O 2 (g) C 12 H 22 O 11 (s) → 12 C (s) + 11 H 2 O (g)

3)Combustion involves the burning of a hydrocarbon in the presence of oxygen to form carbon dioxide and water. C x H y + O 2 → CO 2 + H 2 O 2 C 4 H 10 (l) + 13 O 2 (g) → 8 CO 2 (g) + 10 H 2 O (g) 2 C 10 H 22 (l) + 31 O 2 (g) → 20 CO 2 (g) + 22 H 2 O (g)

4)Single Replacement reactions occur when one element is replaced by another in a compound element + compound → element + compound 3 CuCl 2 (aq) + 2 Al (s) → 3 Cu (s) + 2 AlCl 3 (aq) Zn (s) + H 2 SO 4 (aq) → H 2 (g) + ZnSO 4 (aq)

5) Double Replacement reactions occur when the elements in a solution of reacting compounds exchange places, or replace each other compound + compound  compound + compound CaCl 2 (aq) + 2 AgNO 3 (aq) → Ca(NO 3 ) 2 (aq) + 2 AgCl (s) Pb(NO 3 ) 2 (aq) + KI (aq) → PbI 2 (s) + KNO 3 (aq)

Completing Chemical Reactions Pb(NO 3 ) 4 (aq) + Mg (s)  Identify the type of chemical reaction: single replacement Determine identity of ions: Pb 4+ NO 3 1- Mg 2+ Determine identity of products: Mg(NO 3 ) 2 Pb Write and balance the equation: Pb(NO 3 ) 4 (aq) + 2 Mg (s)  2 Mg(NO 3 ) 2 (aq) + Pb (s)

Completing Chemical Reactions C3H8 (g) + O2 (g) 