Keefe 1415

CHAPTER 11 PART 1: BALANCING EQUATIONS

• The process by which one or more substances are rearranged to form different substances.

WHAT ARE CHEMICAL REACTIONS?

• Reactants Products

Sample: 2Mg (s) + O2(g) 2MgO(s)• Coefficients: Numerals used in an equation to

indicate relative amounts of reactants and products.

COMPONENTS FOR CHEMICAL EQUATIONS

Like INGREDIENTS for a reaction

END RESULT or GOAL for a reaction

WAYS TO DENOTE CONDITIONS FOR REACTIONS.

• When on their own, they exist as a pair of atoms to form a molecule.

• Br2 bromine gas or liquid, I2 iodine gas or crystal , N2

nitrogen gas, Cl2 chlorine gas, H2 hydrogen gas, O2

oxygen gas, F2 fluorine gas

“BrINClHOF”

DIATOMIC MOLECULES“THE MAGNIFICENT SEVEN”

• Word problem: Hydrogen gas and oxygen gas react to yield water vapor

Word equation: Hydrogen (g) + Oxygen(g) Water (l)

• Skeleton equation:

H2(g) + O2(g) H2O(l)

REPRESENTING CHEMICAL EQUATIONS.

BALANCE THE REACTION:

2H2(g) + O2(g) 2 H2O(l)

BALANCING EQUATIONS

• Key Law:

“Conservation of Matter”!• Must have the same number (#) of

atoms (mass) on the reactant side as on the product side!!!

BALANCING EQUATIONS

• Which windows represent (1) the reactants and (2) the products for the following reaction?

• 2NO(g) + O2(g) → 2NO2(g)

QUESTION USING THE LAW OF CONSERVATION OF MATTER.

• Determine the correct formulas and physical states of reactants & products.

• Write a skeleton equation with reactants & products.

• Count atoms for each element in the reactants & products.

• Balance two sides of chemical reaction with whole number coefficients. (NEVER change subscripts for ANY reason!!!)

• Check each element or polyatomic ion is balanced on both sides. Make sure the coefficients are the SIMPLEST whole number ratio!!!

GENERAL SUMMARY STEPS TO BALANCING EQUATIONS.

BALANCING USING A GRID

Al(s) + HCl(aq) H2(g) + AlCl3(s)

Draw the chart:

Elements Reactants Products

Al

H

Cl

USING A GRID WITH POLYATOMICS

Pb(NO3)4 (aq) + CuSO4 (aq) Pb(SO4)2(s) +Cu(NO3)2(aq)

Components Reactant Product

Pb

NO31-

Cu

SO42-

• Yes, but we use the common denominator to convert them to whole numbers.

• Remember, the coefficients are ratios, just like the subscripts for each compound.

CAN COEFFICIENTS BE REPRESENTED AS FRACTIONS?

EXAMPLE OF A COEFFICIENT AS A FRACTION.

C2H6(g) + O2(g) CO2(g) + H2O(l)

Elements Reactant Product

C

H

O

BALANCE THE FOLLOWING REACTIONS:

BALANCE THE FOLLOWING REACTIONS:

WHAT WE MAY LOOK FOR IN A CHEMICAL REACTION!!

• Temperature change (energy change)

• Precipitate forming (solid from two aqueous solutions)

• Formation of a gas

• Smoke (for when it buuuuuurns)

• Color change

• Odor (not best, but possible indicator)

• pH change

TYPES OF REACTIONS1. Synthesis reactions

2. Decomposition reactions

3. Single displacement reactions

4. Double displacement reactions

5. Combustion reactions

6. Neutralization reactions

You need to be able to identify each type.

1. SYNTHESIS

Example C + O2

OO C + O O C

General: A + B AB

EX. SYNTHESIS REACTION

PRACTICE

• Predict the products and balance the reactions.

Na(s) + Cl2(g)

Mg(s) + F2(g)

Al(s) + F2(g) •.

MORE PRACTICE: GIVE THE FORMULAE, PREDICT PRODUCTS, AND BALANCE

• Sulfur dioxide gas is bubbled through water• Solid potassium oxide is added to a

container of carbon dioxide gas• A piece of sodium is added to a container

of iodine vapor

2. DECOMPOSITION

Example: NaCl

General: AB A + B

Cl Na Cl + Na

EX. DECOMPOSITION REACTION

DECOMPOSITION PRACTICE:

• balance:

• H2O ---> H2 + O2

GIVE THE FORMULA, PREDICT THE PRODUCTS, AND BALANCE:

3. SINGLE DISPLACEMENT (AKA SINGLE REPLACEMENT)

Example: Zn + CuCl2

ZnClCl Cu +

General: AB + C AC + B

ClCl Zn Cu+

Zn was oxidized

Went from neutral (0) to (+2)

Cu was reduced

Went from (+2) to Neutral (0)

EX. SINGLE REPLACEMENT REACTION

SINGLE REPLACEMENT REACTIONS• Predict the product and balance the following

single replacement reaction equations:

• Zn(s) + HCl(aq)

• NaCl(s) + F2(g)

• Al(s)+ Cu(NO3)2(aq)

MORE PRACTICE:

4. DOUBLE REPLACEMENT

Example: MgO + CaS

General: AB + CD AD + CB

SOMg Ca

+O S

Mg Ca+

DOUBLE REPLACEMENT REACTIONS

• Think about it like “foil”ing in algebra, first and last ions go together + inside ions go together

• Example:

AgNO3(aq) + NaCl(s) AgCl(s) + NaNO3(aq)

• Another example:

K2SO4(aq) + Ba(NO3)2(aq) KNO3(aq) + BaSO4(s)

PRACTICE• Predict the products. Balance as necessary.

1. HCl(aq) + AgNO3(aq)

2. CaCl2(aq) + Na3PO4(aq)

3. Pb(NO3)2(aq) + BaCl2(aq)

4. FeCl3(aq) + NaOH(aq)

5. KOH(aq) + CuSO4(aq)

COMBUSTION REACTIONS• In general:

CxHy + O2 CO2 + H2O

• Products are ALWAYS

carbon dioxide and water.

COMBUSTION

• Example• C5H12 + O2 CO2 + H2O

• Write the products and balance the following combustion reaction:• C10H22 + O2

MORE PRACTICE:

NEUTRALIZATION

• Acid + base a salt + water• ***acid formulae always start with H• *** bases always end in hydroxide and

START with alkali or alkaline earth metals

• Example: HBr + NaOH ---> NaBr + H2O

PREDICT THE PRODUCT AND BALANCE:

MIXED PRACTICE• State the type, predict the products, & balance.

1. BaCl2 + H2SO4

2. C6H12 + O2

3. Zn + CuSO4

4. Cs + Br2

5. FeCO3

6. NH4OH + HBr