Unit Nine:Chemical Reactions

chemical reactions

Timely news related to chemistry:

• This is just one reason why understanding some chemistry is important to our daily lives.

• Ferric chloride (FeCl3)• Nitric Acid (HNO3) • Both are corrosive materials used to etch metal.

Chemistry in the news: explosion in Spain

Chemical Reactions:

• A chemical reaction is the process by which one or more substances are changed into one or more different substances. In a chemical reaction, the original substances are called the reactant and the resulting substances are called the product. A chemical reaction is described by chemical equations.

• Basic Structure of a chemical reaction:

Reactants Products

Interpreting Chemical Equations:

• Chemical reactions can be written as word equations or as formula equations. • Underline the reactant(s) and circle the product(s) in the following examples:

• Iron reacts with oxygen to produce iron oxide (rust). (Word equation)

• 2Fe(s) + O2(g) FeO(s) (Formula equation

• Iron reacts with oxygen to produce iron oxide (rust). (Word equation)

• 2Fe(s) + O2(g) FeO(s) (Formula equation)

Observations about writing chemical reaction:

1. The reactants are always written to the left of the yield arrow () and the products are always written to the right.

2. Chemical formulas are still written using the criss-cross method.

3. Formula equations are balanced using coefficients which are written in front of the chemical formula.

Symbols and Chemical Equations:

• Yield arrow

• (s) solid

• (l) liquid

• (g) gas

• (aq) Aqueous: water solution

Reactant(s) Products

Pb(NO3)2(aq) + KI (aq) PbI2(s) + 2KNO3(aq)

Lead iodide: ____________ Potassium nitrate: ________

Potassium iodide: ________ Lead nitrate : ___________

Pb (NO3)2(aq) + KI (aq) PbI2(s) + 2KNO3(aq)

Lead iodide: Product Potassium nitrate: Product

Potassium iodide: Reactant Lead nitrate : Reactant

Recognizing types of reactions:

• There are five types of reaction that fit the following patterns:

1. Synthesis A + B AB2. Decomposition AB A + B3. Single replacement A + BC AC + B4. Double replacement AB + CD AD + CB

5. Combustion: CxHy + O2 CO2 + H2O

Types of reactions

Pb(NO3)2(aq) + KI (aq) PbI2(s) + 2KNO3(aq)

AB + CD AD + CB

Double replacement!

Writing Chemical Reaction:

• Reactants : Lead(II) nitrate (aq) + Potassium iodide

• Products: Lead(II) iodide + Potassium nitrate

Pb (NO3)2(aq) + KI (aq) ____________ + 2KNO3(aq)

Your job: determine the formula and state of Lead (II) iodide

Pb2+ = ________I- = ___________

Formula = ____________

Balancing Chemical Reactions:

• Since matter is neither created nor destroyed during a chemical

reaction (Law of Conservation of Mass), it is necessary to balance the

elements in a chemical equation. This is done using coefficients.

Coefficients do not change the chemical formula but the do change

the amount of each substance.

Coefficients & Counting!

• Remember this?

3H2O = ____ H, _____ O

2Al2(SO4)3 = ______ Al, _____S, ____ O

• Answers

3H2O = 6 H, 3 O

2Al2(SO4)3 = 4 Al, 6 S, 24 O