Chemical Reactions What has to be true if one occurred? The chemical identity of the matter involved must change. This means that the matter after the reaction has different properties than the matter before the reaction. How might I know if this happened? The temperature changes. The color changes. A gas is formed as evidenced by bubbles. A solid (precipitate) is formed from solutions. The smell changes (an odor is produced or diminishes). Light is emitted in the process. ETC…

Balancing Chemical Equations Why do we need to worry about it??? THE LAW OF CONSERVATION OF MASS! What are chemical equations??? Chemical “recipes” that describe reactions and the species involved. How do we do it??? By writing down all the correct chemical formulas and using COEFFICIENTS, not subscripts, to make the same number of atoms of each element on both sides of the equation.

Easiest…When all species are given. Simply count the number of each element (or polyatomic unit if unchanged on each side) and use COEFFICIENTS to make changes until the same number of atoms is on each side of the equation. If necessary, reduce coefficients to the lowest whole number ratio when finished. Fractions may be used as coefficients ,if desired, unless otherwise prohibited. EXAMPLE Al + Cl2  AlCl3 Al Cl 2 3 2 2 1 1 2 6 6 2 3

- More Difficult - species must be translated Write correct formulas for all species first…then balance like before. REMEMBER DIATOMIC 7…H2 , N2 , O2 , F2 , Cl2 , Br2 , I2 Example Sodium metal is placed in water and produces sodium hydroxide and hydrogen gas as it reacts. Na + H2O  NaOH + H2

- More Difficult - species must be translated Write correct formulas for all species first…then balance like before. REMEMBER DIATOMIC 7…H2 , N2 , O2 , F2 , Cl2 , Br2 , I2 Example Sodium metal is placed in water and produces sodium hydroxide and hydrogen gas as it reacts. Na + H2O  NaOH + H2

- Most Complicated - only reactants are given Products must be predicted using a knowledge of basic chemical reaction patterns. You are responsible for five patterns… Synthesis / Addition / Combination two or more become one

SYNTHESIS / ADDITION / COMBINATION Example: Sodium metal violently reacts with fluorine gas.

SYNTHESIS / ADDITION / COMBINATION Example: Sodium metal violently reacts with fluorine gas. Nonmetal oxide + H2O  oxyacid

- Most Complicated - only reactants are given Products must be predicted using a knowledge of basic chemical reaction patterns. You are responsible for five patterns… Synthesis / Addition / Combination two or more become one Decomposition one becomes two or more

Decomposition Metallic carbonates break down to yield metallic oxides and carbon dioxide. Metallic chlorates break down to yield metallic chlorides and oxygen. Metallic sulfites break down to yield metallic oxides and sulfur dioxide. Hydrogen peroxide decomposes into water and oxygen. Sulfurous acid decomposes into water and sulfur dioxide. Carbonic acid decomposes into water and carbon dioxide. Hydrated salts decompose into the salt and water. Ex. Na2CO3.H2O  Na2CO3 + H2O

Carbonates: XCO3 → XO + CO2 Example: Na2CO3(s) --> Na2O(s) + CO2(g) Chlorates: XClO3 → XCl + O2 Example: 2LiClO3(s) --> 2LiCl(s) + 3O2(g)

DECOMPOSITION Example: Potassium chlorate rapidly breaks down when heated.

DECOMPOSITION Example: Potassium chlorate rapidly breaks down when heated.

- Most Complicated - only reactants are given Products must be predicted using a knowledge of basic chemical reaction patterns. You are responsible for five patterns… Synthesis / Addition / Combination two or more become one Decomposition one becomes two or more Single Replacement element displaces a like element from a compound

SINGLE REPLACEMENT Example: Aluminum metal reacts with a copper(II) chloride solution.

SINGLE REPLACEMENT Example: Aluminum metal reacts with a copper(II) chloride solution.

SINGLE REPLACEMENT Example: Sodium metal violently reacts with water.

SINGLE REPLACEMENT Example: Sodium metal violently reacts with water.

- Most Complicated - only reactants are given Products must be predicted using a knowledge of basic chemical reaction patterns. You are responsible for five patterns… Synthesis / Addition / Combination two or more become one Decomposition one becomes two or more Single Replacement element displaces a like element from a compound Metathesis / Double Replacement two compounds make two new compounds, often in solution

METATHESIS / DOUBLE REPLACEMENT Example: Solutions of calcium chloride and silver nitrate are mixed.

METATHESIS / DOUBLE REPLACEMENT Example: Solutions of calcium chloride and silver nitrate are mixed. Double replacement reactions will produce one solid based on solubility rules https://www.youtube.com/watch?v=dXqelH1MxGw

- Most Complicated - only reactants are given Products must be predicted using a knowledge of basic chemical reaction patterns. You are responsible for five patterns… Synthesis / Addition / Combination two or more become one Decomposition one becomes two or more Single Replacement element displaces a like element from a compound Metathesis / Double Replacement two compounds make two new compounds, often in solution Complete Hydrocarbon Combustion hydrocarbon and oxygen become CO2 and H2O

COMPLETE HYDROCARBON COMBUSTION Example: Octane is completely burned.

COMPLETE HYDROCARBON COMBUSTION Example: Octane is completely burned.

Practice