Unit 6: Life on the Bay Name: __________________________________ Unit Notes Class Period: _____________________________

A. Introduction to Chemical Equations

Chemists use a chemical equation—a quick, shorthand notation—to convey as much

information as possible about what happens in a chemical reaction.

Word Equations

How do you describe what happens in a chemical reaction?

• In a word equation, write the names of the reactants to the left of the arrow, separated

by plus signs.

Ex.

1. Describe rusting of Iron using chemical equation.

2. Write a chemical equation of the decomposition of hydrogen peroxide to form

water and oxygen.

3. Write a chemical using of the combustion of methane to form carbon dioxide and

water.

What is a chemical equation?

What is a skeleton equation?

Unit 6: Life on the Bay Name: __________________________________ Unit Notes Class Period: _____________________________

Parts of a Chemical Reaction

Example:

1. Hydrochloric acid reacts with solid sodium hydrogen carbonate. The products formed

are aqueous sodium chloride, water, and carbon dioxide gas. Write a skeleton equation

for this chemical reaction.

What is the advantage of using a Chemical Equation?

Unit 6: Life on the Bay Name: __________________________________ Unit Notes Class Period: _____________________________

Balancing Chemical Equations

A chemical reaction is also described by a balanced equation in which each side of the

equation has the same number of atoms of each element and mass is conserved.

o As reactants are converted to products, the bonds holding the atoms together are

broken, and new bonds are formed.

o The atoms themselves are neither created nor destroyed; they are merely rearranged.

o In any chemical change, mass is conserved.

o The law of conservation of mass states that mass is neither created nor destroyed.

o In order to show that mass is conserved during a reaction, a chemical equation must be

balanced.

Examples:

1. Carbon burns in the presence of oxygen to produce carbon dioxide.

o This equation is balanced.

o You do not need to change the coefficients.

o They are all understood to be 1.

2. When hydrogen and oxygen are mixed, the product is water.

- The formulas for all the reactants and the product are correct, but this equation is not

balanced. Write the balanced equation below.

Unit 6: Life on the Bay Name: __________________________________ Unit Notes Class Period: _____________________________

The reaction between oxygen and hydrogen in fuel cells produces the energy to power a car. What are

the products of the reaction in a fuel cell that make the fuel-cell car a zero-emission car?

Water is the product of the reaction between oxygen and hydrogen in a fuel cell. Water is not a

pollutant, and so fuel-cell cars are considered “zero-emission” cars.

How to Balance Chemical Equations:

When balancing an equation, there are a few rules to remember:

o The subscripts of the molecules can never be altered. Only coefficients can be added.

o The coefficient placed in front of a molecule applies to all elements that make up

that molecule.

o The number of atoms can be found by multiplying the coefficient by the subscript of the

element. If no subscript appears, a subscript of 1 should be assumed.

o Molecules made up of many elements should have coefficients added first, with single

elements remaining until last.

o If a molecule is placed in parentheses with a subscript outside the parentheses, the

subscript applies to all elements within the parentheses. If an element within the

parentheses

has a subscript, then you will multiply the subscripts to get the number of atoms.

Unit 6: Life on the Bay Name: __________________________________ Unit Notes Class Period: _____________________________

Now it’s your turn to practice balancing chemical equations. Remember that you will multiply

the coefficients by the subscripts to get the total number of atoms.

1. Balance the equation for the reaction of benzene and hydrogen to form cyclohexane.

C6H6 + H2 → C6H12

2. Balance the equation for ethane, C2H6, burning in oxygen to form carbon dioxide

and steam.

C2H6 + O2 → CO2 + H2O

3. Balance this chemical equation.

Fe2O3 + H2SO4 → Fe2(SO4)3 + H2O

4. Balance the equation for aluminum burning in oxygen to form aluminum oxide.

Al + O2 → Al2O3

Unit 6: Life on the Bay Name: __________________________________ Unit Notes Class Period: _____________________________

5. Balance the equation for ammonium carbonate so that it breaks down into gaseous

ammonia, carbon dioxide, and steam.

(NH4)2CO3 → NH3 + CO2 + H2O

6. Balance the following chemical equations.

a. Na(s) + H2O(l) → NaOH(aq) + H2(g)

b. AgNO3(aq) + Zn(s) → Zn(NO3)2(aq) + Ag(s)

Unit 6: Life on the Bay Name: __________________________________ Unit Notes Class Period: _____________________________

Unit 6: Life on the Bay Name: __________________________________ Unit Notes Class Period: _____________________________

B. Types of Chemical Reactions

List evidences of Chemical Reactions

What are the five general types of chemical reactions?

Not all chemical reactions fit uniquely into one category.

o Occasionally, a reaction may fit equally well into two categories.

o Patterns of chemical behavior will become apparent and allow you to predict the

products of reactions.

Single Replacement Reactions

Write the balanced chemical equation of the reaction of Potassium with water producing

Potassium hydroxide and hydrogen gas.

Write the balanced chemical equation of the reaction between zinc and copper II nitrate

producing zinc nitrate and copper.

The two reactions are examples of single replacement reaction. What is Single Replacement

Reaction?

Unit 6: Life on the Bay Name: __________________________________ Unit Notes Class Period: _____________________________

How will you identify a single replacement reaction?

More examples: Assume that the following reactions will occur, write the products and balance

the equation.

1. Lithium and calcium oxide

2. Aluminum and hydrochloric acid

3. Sodium + Calcium oxide

4. Zinc + Lead (II) nitrate

5. Magnesium bromide + Chlorine

Unit 6: Life on the Bay Name: __________________________________ Unit Notes Class Period: _____________________________

A halogen can also replace another halogen from a compound.

o The activity of halogens decreases as you go down Group 7A of the

periodic table—fluorine, chlorine, bromine, and iodine.

o Bromine is more active than iodine, so this reaction occurs:

Br2(aq) + 2NaI(aq) → 2NaBr(aq) + I2(aq)

o But bromine is less active than chlorine, so this reaction does not occur:

Br2(aq) + NaCl(aq) → No reaction

o The activity series of metals lists

metals in order of decreasing

reactivity.

o A reactive metal will replace any

metal listed below it in the activity

series.

Unit 6: Life on the Bay Name: __________________________________ Unit Notes Class Period: _____________________________

Double Replacement Reaction

General Format:

What is the other name?

For a double-replacement reaction to occur, one of the following is usually true:

Writing Equations for Double-Replacement Reactions

A precipitate of barium carbonate is formed when aqueous solutions of barium chloride react

with potassium carbonate. Write a balanced chemical equation for the double-replacement

reaction.

Unit 6: Life on the Bay Name: __________________________________ Unit Notes Class Period: _____________________________

• Using the solubility table, indicated whether the following compounds are soluble or

insoluble. If soluble write (aq) after the given formula. If insoluble write (s) after the

formula.

1. KNO3 4. NaOH

2. HCl 5. K2SO4

3. CaPO4 6. AgI

For each of the following reactions, predict the products, balance the equation, write the net

ionic equation, and identify the spectator ions.

Example:

AgNO3 + KCl ________ + ________

Calcium fluoride and sulfuric acid

Lead II nitrate and sodium iodide