Chapter 21 Chapter 21 Chemical Chemical EquationsEquations

Section 1 Section 1 Chemical ChangeChemical Change

What is a chemical What is a chemical reaction?reaction?

A. Describing chemical A. Describing chemical reactionsreactions

1.1. Chemical Reactions- change of one or more Chemical Reactions- change of one or more substances converted into new substancessubstances converted into new substances

2.2. Reactants - substances that combine or Reactants - substances that combine or changechange

3.3. Products- new substances that are Products- new substances that are producedproduced

produceproduce

Reactants Reactants Products Products

B. Conservation of Mass B. Conservation of Mass

1.1. Conservation of Mass-a law which Conservation of Mass-a law which states that, in a chemical reaction, states that, in a chemical reaction, mass is not created or destroyed; it mass is not created or destroyed; it stays the samestays the same

2.2. Antione Lavoisier – Father of Antione Lavoisier – Father of Modern ChemistryModern Chemistry

1.1. Found mass of products equaled the Found mass of products equaled the mass of the reactantsmass of the reactants

C. Writing Equations C. Writing Equations

1.1. Chemical equation - uses chemical formulas Chemical equation - uses chemical formulas and symbols and symbols to describe a chemical reaction to describe a chemical reaction and the products it producesand the products it produces

1.1. Chemical formula - expresses the relationship Chemical formula - expresses the relationship between elementsbetween elements in the compounds and in the compounds and molecules they make upmolecules they make up

1.1. Symbols used to show physical Symbols used to show physical state of state of reactantsreactants; ; (s) solids (aq) aqueous (g) gas (l) (s) solids (aq) aqueous (g) gas (l) liquidliquid

C. Writing Equations C. Writing Equations

4.4. Coefficients – whole numbers in front Coefficients – whole numbers in front of the symbolof the symbol, which represent the , which represent the number of units of each substance in a number of units of each substance in a reactionreaction ****Located before the symbolsLocated before the symbols

5.5. Subscripts – small lowered numbers Subscripts – small lowered numbers which represent the number of atoms which represent the number of atoms in a molecule of a particular elementin a molecule of a particular element

*Located after and below the symbols*Located after and below the symbols6.6. Nomenclature – way to name things Nomenclature – way to name things

scientificallyscientifically

Discussion QuestionsDiscussion Questions

1.1. What does the law of conservation What does the law of conservation of mass state?of mass state?

1.1. What is the function of coefficients What is the function of coefficients in a chemical equation?in a chemical equation?

AnswersAnswers

In a chemical reaction, matter is In a chemical reaction, matter is neither created nor destroyed. The neither created nor destroyed. The total sum of the reactants must total sum of the reactants must equal the sum of the product.equal the sum of the product.

Chemist need to know how much of Chemist need to know how much of a reactant will produce a certain a reactant will produce a certain amount of productamount of product

Describe 3 chemical reactions that Describe 3 chemical reactions that you have observed (EX: burning you have observed (EX: burning marshmallow)marshmallow)

There are many things that let you There are many things that let you know itknow it’’s a chemical reaction: color s a chemical reaction: color change, forming a precipitate, change, forming a precipitate, production of heat.production of heat.

Section 2Section 2Chemical Chemical EquationsEquations

Checking for Balance Checking for Balance

1.1. A balanced chemical reaction- both A balanced chemical reaction- both sides of equation have the same sides of equation have the same number of atoms of each elementnumber of atoms of each element

2.2. Coefficients are used in front of the Coefficients are used in front of the element or compound to balance.element or compound to balance.

3.3. Choosing coefficients - becomes easier Choosing coefficients - becomes easier with practice; trial and error at firstwith practice; trial and error at first

Writing balanced Writing balanced chemical equations - 4 chemical equations - 4

step processstep process1.1. Describe the reaction in wordsDescribe the reaction in words

2.2. Write the equation using formulas Write the equation using formulas and symbolsand symbols

3.3. Check for balanceCheck for balance

4.4. Add coefficients where needed for Add coefficients where needed for balancebalance

Discussion QuestionDiscussion Question

Why do chemical equations need to Why do chemical equations need to be balanced?be balanced?

AnswerAnswer

Law of conservation of mass says Law of conservation of mass says mass will not be created or mass will not be created or destroyeddestroyed

Section 3Section 3Classifying Classifying Chemical Chemical ReactionsReactions

Types of ReactionsTypes of Reactions1. Synthesis Reaction- two or more substance form a new

substance A + B --> AB2. Decomposition Reaction-One substance breaks down

into two or more substances AB ---> A + B

3. Single-displacement Reaction- one element replaces another one in a compound; A + BC ---> AC +B or D + BC --> BD + C

4. Double-displacement Reaction- results if a precipitate, water, or a gas forms when two ionic compounds in a solution are combined; AB + CD --> AD + CB

5. Combustion Reaction-a substance combines with oxygen to produce energy

“X ” + O2 --> CO2 + H2O

Oxidation-Reduction Oxidation-Reduction (Redox)(Redox)

These reactions often These reactions often involve oxygeninvolve oxygen Oxidation

Loss of electrons Substance becomes “oxidized”

Reduction Gain of electrons Substance becomes “reduced”

Discussion QuestionsDiscussion Questions

1. What two chemical reactions are 1. What two chemical reactions are ““oppositesopposites”” of each other and why? of each other and why?

2. What are the 5 types of chemical 2. What are the 5 types of chemical reactions?reactions?

AnswersAnswers

Synthesis and decompositionSynthesis and decomposition synthesis multiple substances combine synthesis multiple substances combine

to form a new oneto form a new one decomposition a single substance decomposition a single substance

breaks apart into multiple simpler breaks apart into multiple simpler substancessubstances

Synthesis, decomposition, single-Synthesis, decomposition, single-displacement, double-displacement, displacement, double-displacement, combustioncombustion

Section 4 Section 4 Chemical Chemical

Reactions and Reactions and EnergyEnergy

A. Chemical Reactions A. Chemical Reactions involve energy exchangeinvolve energy exchange

1.1. Exergonic-Breaking chemical bonds Exergonic-Breaking chemical bonds release energyrelease energy

2.2. Endergonic-Forming chemical bonds Endergonic-Forming chemical bonds requires energyrequires energy

3.3. Exothermic-Chemical Reaction where Exothermic-Chemical Reaction where energy is primarily given off in the form energy is primarily given off in the form of heatof heat

4.4. Endothermic-Chemical reaction that Endothermic-Chemical reaction that requires heat energy in order to proceedrequires heat energy in order to proceed

B. More energy outB. More energy out

1.1. A catalyst speeds up a chemical reaction A catalyst speeds up a chemical reaction without itself being permanetly changedwithout itself being permanetly changed

2.2. An inhibitor prevents or slows a An inhibitor prevents or slows a chemical reaction or interferes with the chemical reaction or interferes with the catalystcatalyst’’s actions action

Discussion QuestionDiscussion Question

How are chemical bonds involved in How are chemical bonds involved in energy exchanges?energy exchanges?

AnswerAnswer

Breaking bonds release energy; Breaking bonds release energy; forming bonds to require energyforming bonds to require energy