Section 3.1 Chemical Equations

Review: Element Symbols All elements are represented by a 1 or 2 letter symbol For example C = Carbon Ne = Neon O = Oxygen The symbols are shown on the periodic table

Review: Chemical Formulas Shows the elements & number of atoms of each element in a molecule H2SO4 Elements Hydrogen; 2 atoms Sulfur: 1 atom Oxygen: 4 atoms 7 atoms total Subscript

Coefficients A formula may begin with a number. If there is no number, then “1” is understood to be in front of the formula. This number is called the coefficient. The coefficient represents the number of molecules of that compound or atom needed in the reaction. For example: 2H2SO4 – 2 molecules of Sulfuric Acid

Coefficients 2H2SO4 – 2 molecules of Sulfuric Acid A coefficient is distributed to ALL elements in a compound 2 – H2 (for a total of 4 H atoms) 2 – S (for a total of 2 S atoms) 2 – O4 (for a total of 8 O atoms)

Chemical Equations A chemical equation is written as an expression similar to a mathematic equation that can be compared to a recipe that a chemist follows in order to produce desired results.

Chemical Equations All chemical equations have reactants and products. We express a chemical equation as follows: Reactants  Products The arrow is equivalent to an “=“ math. When we describe the equation we use the word “yields” or “produces” instead of equals

The burning of methane gas in oxygen is: Equation Example: The burning of methane gas in oxygen is: CH4 + 2 O2 → CO2 + 2 H2O

Conservation of matter The law of conservation of matter tells us that matter can neither be created nor destroyed. It is transformed from one form to another. We follow the conservation of matter law when we balance equations.

Balancing a Chemical Equation A chemical equation is balanced when the ions or atoms found on the reactant side of the equation equals that found on the product side. The arrow can be considered the balance point.

Coefficients We use coefficients in front of elements or compounds on either side of the reaction to balance the equation. (The coefficients go in front of the chemical!) We cannot change subscripts because it would create new materials that are not part of reaction process.

Balance this equation! Na + Cl2 NaCl Na- 1 Na-1 Cl- 2 Cl-1 **note that the number of sodium balances but the chlorine does not. We will have to use coefficients in order to balance this equation.

Inserting subscripts Na + Cl2 2 NaCl Na- 1 Na-1 2 Cl- 2 Cl-1 2 ** Now the chlorine balances but the sodium does not! So we go back and balance the sodium.

Finally balanced! 2Na + Cl2 2 NaCl Na- 1 2 Na-1 2 Cl- 2 Cl-1 2 **Since the number of each element on the reactant side and the product side of the equation are equal, the equation is balanced.

Balancing Equation Practice CuCl3 + Li2S  Cu2S3 + LiCl NiNO3 + KCl  NiCl + KNO3 FeCl3 + Na2O  Fe2O3 + NaCl

Answers: 1. 2CuCl3 + 3Li2S  Cu2S3 + 6LiCl 2. NiNO3 + KCl  NiCl + KNO3 (already balanced) 3. 2FeCl3 + 3Na2O  Fe2O3 + 6NaCl

Simple Patterns of Chemical Reactivity Section 3.2 Simple Patterns of Chemical Reactivity

Identifying Reaction Types Reactions are classified by their products. There are several different types of chemical reactions. The 5 basic types of chemical reactions we will study are: synthesis or combination reactions, decomposition reactions, single replacement reactions, double replacement reactions, and combustion reactions.

Combination or Synthesis reactions Synthesis (meaning to make) or combination reactions are typified by their single product. If you have a reaction in which at least 2 elements or compounds are reacted and produce a single product, the reaction is a synthesis reaction.

Synthesis Reactions A + B  AB Note: Single Product! This is your clue that this is a synthesis or combination reaction.

Decomposition Reactions Decomposition reactions are really just the opposite of a synthesis reaction. Remember, if you can make a substance, you should be able to break it back apart into its components. A good way to remember decomposition reactions to to remember what happens when something decomposes. It falls apart!

Decomposition Reactions AB  A + B Note: Single Reactant! The single reactant is your clue that this is a decomposition reaction.

Single Replacement Reactions Single replacement reactions occur when one chemical takes the place of another in a reaction. In the typical single replacement reaction, an element trades places with one of the ions in a compound.

Single Replacement Reactions A + CD  AD + C Note: Element A replaces ion C in the reaction. The clue in this reaction is: Element+Compound  Element + Compound

Double Replacement Reactions Double replacement reactions are identified by two ions trading places and forming new compounds.

Double Replacement Reactions AB + CD  AD + CB Note: Notice that one ion from compound AB replaces one ion from compound CD. Clue: Compound+CompoundCompound+Compound

Combustion Reactions Combustion reactions are the ones that burn (or explode!). Most involve O2 as a reactant These reactions are identified by their products. They either produce carbon dioxide and water. Hydrocarbons compounds are very combustible.

Combustion Reactions CH4 + O2  CO2 + H2O They may also be written: CH4  CO2 + H2O (O2 is usually written above the arrow.) Clue: CO2 (carbon dioxide) in the product along with water