CONQUER THE CHEMISTRY EOC:

BALANCING EQUATIONS AND STOICHIOMETRY

Chemistry TEKS8 (A) define and use the concept of a mole;8 (B) use the mole concept to calculate the

number of atoms, ions, or molecules in a sample of material;

8 (C) calculate percent composition and empirical and molecular formulas;

8 (D) use the law of conservation of mass to write and balance chemical equations; and

8 (E) perform stoichiometric calculations, including determination of mass relationships between reactants and products, calculation of limiting reagents, and percent yield.

IPC TEKS7(C) demonstrate that mass is conserved when

substances undergo chemical change and that the number and kind of atoms are the same in the reactants and products;

7(D) analyze energy changes that accompany chemical reactions such as those occurring in heat packs, cold packs, and glow sticks and classify them as exothermic or endothermic reactions;

8th TEKS5(D) recognize that chemical formulas are used to

identify substances and determine the number of atoms of each element in chemical formulas containing subscripts;

5(E) investigate how evidence of chemical reactions indicate that new substances with different properties are formed; and

5(F) recognize whether a chemical equation containing coefficients is balanced or not and how that relates to the law of conservation of mass.

Label the Parts of an Equation

Why Balance Equations?

Law of Conservation of Mass – Matter cannot be created or destroyed it can only change forms.

In chemical reactions the number and mass of atoms on the reactant side of the equation must equal the number and mass of atoms on the product side of the equations.

Chemical Equations

• Recipe for a chemical reaction• Relative number of reactants and products

– Coefficients represent the relative numbers.

CH4 + 2O2 CO2 + 2H2O

Law of Conservation of Matter: Balancing

Chemical Equations• Atoms are conserved in a chemical reaction.• Coefficients are manipulated to balance

chemical reactions and create equivalent measures.

• Identities cannot be changed.

_C2H5OH (l) + _O2 (g) _CO2 (g) + _H2O (g)

BalancingChemical Equations

C2H5OH (l) + O2 (g) CO2 (g) + H2O (g)

Count Atoms:Carbon 2 Carbon 1

Hydrogen 6 Hydrogen 2

Oxygen 3 Oxygen 3

BalancingChemical Equations

C2H5OH (l) + O2 (g) CO2 (g) + H2O (g)

C2H5OH (l) + 3O2 (g) 2CO2 (g) + 3H2O (g)

Chemical Equations as EquivalentsCoefficients from a balanced equation

represent the number of theoretical mole equivalents and can be used in stoichiometric calculations.

8TH GRADE RELEASED QUESTION

Jelly Bean Equations

andChemical Equation

Cards

Online Balancing Equation Practice

http://sciencespot.net Click Kid Zone Click Matter & Atoms

Go to: Balancing Equations Online

Balancing Equations Online 2

http://funbasedlearning.com/chemistry/chemBalancer3/worksheet.htm

Balancing Equation Strips

Draw a stripBalance the equationWrite a word equation describing the reaction

Make or demonstrate a representation of the equation

Chemical Reaction

Types

Synthesis(Combination, Composition)

Two or more substances combine to form a single substance.

General equation:A + B AB

example:2Na + Cl2 2NaCl

Decomposition

A compound is broken into two or more products.

General equation:AB A + B

example:2H2O 2H2 + O2

Single Replacement

A + BC AC +B

Activity Series

For an element to replace another the lone element must be more active than the element it is replacing in the substance.

See the reference chart behind your periodic table.

Example: Zn+ 2 HCl ZnCl2 + H2

Example: Thermite Reaction

2 Al + Fe2O3 Al2O3 + 2 Fe

Example:

2NaBr (aq) + Cl2 (g) 2NaCl (aq) + Br2 (g)

Double Replacement(Double Displacement)

AB + CD AD + CB

Double Replacement Reactions

Occur in aqueous solutions For a DR reaction to occur one of the

following must happen:1. A precipitate is formed (an insoluble or

slightly soluble solid).2. A molecular compound (usually water is

formed).3. A gas is formed.4. Follow Solubility Rules

Example: Production of a Precipitate

Silver Nitrate + Sodium Chloride

Precipitate

AgCl (s)

Chemistry Released

Chemistry Released

STOICHIOMETRY DIMENSIONAL ANALYSIS

The Mathematics of Chemistry

Stoichiometric Calculation Plan

Write the chemical equationBalance the chemical equationFollow the steps of dimensional analysis

Start with what is given Set up a series of equivalent measures End with your goal Solve the problem by cancelling units Record the appropriate answer with units

Stoichiometry Stoichiometry is a branch of chemistry that

deals with the relative quantities of reactants and products in chemical reactions.

Greek root words: Stoicheion meaning " element“ Metron meaning "measure"

What is Dimensional Analysis?

Using the units, or dimensions, of measurements to express and calculate chemical quantities

What is the relationship?

Dimensional analysis is a strategy used for doing stoichiometric calculations.

What are some common equivalent measurements?

1 inch =______centimeter(s)1 week = ______ day(s)60 seconds = ______minute(s)1 lb =______ ounce(s)1 cup = _____ fluid ounces1 tablespoon = _____ teaspoon(s)4 quarts = _____ gallon(s)

Common Equivalent Measurements

1 mile = _____ feet1 kg = _____ 2.2 lb1 ft = ____ inches365 days = _____ year(s)1 ton = _____ pounds

Dimensional Analysis –The Plan

1. What is given? Start your calculation with this quantity with units.

2. What is your goal? What you are solving for is your goal and should be on top of the last step of the problem.

3. Set up a series of equivalent measures that cancels out all units except the goal units.

4. Solve the problem, and remember to mark through the cancelled units.5. Record the appropriate answer with units.

Give it a try!How many seconds are there in 5.5 days?

Follow the steps:1.What is given? 5.5 days2.What is your goal, and what are the units?

Determine # of seconds in 5.5 days3.Set up a series of equivalent measure that

cancels out all units except the goal units.

Get started: **What fractions “equal to 1” help transition from

days to seconds?

Give it a try!

5.5 days X 24 hours X 60 minutes X 60 seconds= ? seconds 1 1 day 1 hour 1 minute 1

4.Record the appropriate answer with units.

What are some common equivalent measurements in chemistry?

1,000 g = _____kg100 cm = ______ m1 m = _____dm1 L = _____ml1 mole = _______ particles/atomsmolar mass = _____ mole(s)Avogadro’s number = _____ mole(s)

Mole equivalents

MOLE

PART ICLES

GRAMS

Avogadro’s Number Molar

Mass

Molar MassThe mass in grams of 1 mole of the

compound

C10 H6 O3 10 C = 10 X 12.011g = 120.11 6 H = 6 X 1.008g = 6.048 3 O = 3 X 15.999g = 48.997

TOTAL = *175.16 grams

*Remember the significant figures rules.

Molar MassThe mass in grams of 1 mole of the

compound calcium carbonate

CaCO3 Ca 1 X 40.078 grams = 40.078 grams C 1 X 12.011 grams = 12.011 grams O 3 X 15.999 grams = 47.997 grams

TOTAL = *100.086 grams

*Remember the significant figures rules.

Give it a try!

How many grams are in 4.92 moles of calcium carbonate?

Stoichiometric Calculations –The Plan

1. Write the chemical equation.2. Balance the chemical equation.3. *Follow steps to dimensional analysis:

Start with what is given. Set up a series of equivalent measures. End with your goal. Solve the problem by cancelling units. Record the appropriate answer with units.

Give it a try!Stoichiometric Calculations

4.92 mol CaCO3 X 100.086g CaCO3 = 1 mol CaCO3

Stoichiometry Basics

Mole RatiosMeasuring MolesThe Mathematics of Chemistry FormatGreat Stoichiometry Relay RaceThink, Pair, Share

Limiting Reactants for Recipes

Stoichiometry chocolate chip cookies

Yum!!

Stoichiometric Calculations – The Plan

1. Write the Chemical Equation.2. Balance the Chemical Equation.3. Follow steps to Dimensional Analysis:

Start with what is given. Set up a series of equivalent measures. End with your goal. Solve the problem by cancelling units. Record the appropriate answer with units.

Stoichiometric Calculations – The Problem

Lithium hydroxide is used in an outer space environment to remove excess exhaled carbon dioxide from the living environment. The products of the reaction are lithium carbonate and water. If 48.0 grams of lithium hydroxide are used in a small scale experimental device, how much carbon dioxide will the device process?

The Plan:

1. Write the chemical equation.2. Balance the chemical equation.3. Follow steps to dimensional analysis:

Start with what is given. Set up a series of equivalent measures. End with your goal. Solve the problem by cancelling units. Record the appropriate answer with

units. * Remember Significant Figures.

Stoichiometric Calculations – The Plan

LiOH + CO2 (g) Li2CO3 + H2O (g)

2. Balance the chemical equation.

1. Write the chemical equation.

2 LiOH + CO2 (g) Li2CO3 + H2O (g)

Stoichiometric Calculations –The Plan

2 LiOH + CO2 (g) Li2CO3 (g) + H2O (g)

48.0 g LiOH X 1 mole LiOH X 1 mole CO2 X 44.009g CO2 = 1 23.948 g LiOH 2 mole LiOH 1 mole CO2

3. Follow steps to dimensional analysis:

Stoichiometric Calculations – The Answer

When 48.0 grams of lithium hydroxide are available for use in a reaction, 44.1 grams of carbon dioxide can be processed by the reaction.

*Remember the significant figures.

W R I T E Y O U R O W N S T O I C H I O M E T RY Q U E S T I O N F O R T H I S R E A C T I O N , A N D S W I T C H W I T H Y O U R TA B L E

PA R T N E R :

B A R I U M C H L O R I D E R E A C T S W I T H S O D I U M S U L FAT E I N A P R E C I P I TAT I O N R E A C T I O N T O M A K E B A R I U M

S U L FAT E .

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