Chapter 7 Chemical Reactions Section 7.1 Describing Reactions Section 7.2 Types of Reactions.

Chapter 7 Chemical Chapter 7 Chemical ReactionsReactions

Section 7.1 Describing ReactionsSection 7.1 Describing Reactions

Section 7.2 Types of ReactionsSection 7.2 Types of Reactions


Chemical EquationsChemical Equations

** In order to understand chemical reactions, you ** In order to understand chemical reactions, you first must be able to describe them.first must be able to describe them.

Chemical equations are a useful way of describing Chemical equations are a useful way of describing a change a change to state what is present before and after to state what is present before and after the changethe change..

Chemical rxns contain reactants and products.Chemical rxns contain reactants and products.

ReactantsReactants- the substances that undergo change- the substances that undergo change

ProductsProducts- the new substances formed as a result - the new substances formed as a result of that changeof that change


Using Equations to Represent ReactionsUsing Equations to Represent Reactions

During a chemical reaction, During a chemical reaction, reactants change reactants change into into products.products.

Word equation: ReactantsWord equation: Reactants→→ProductsProducts

→ → ((yields, forms, creates)yields, forms, creates)

Chemical equation-a representation of a Chemical equation-a representation of a chemical reaction in which the reactants and chemical reaction in which the reactants and products are expressed as formulasproducts are expressed as formulas


Conservation of MassConservation of Mass

During chemical reactions, During chemical reactions, the mass of the the mass of the products is always equal to the mass of the products is always equal to the mass of the reactants.reactants.

Antoine Laviosier (1743-1794)-established the Antoine Laviosier (1743-1794)-established the law of conservation of masslaw of conservation of mass

Key Concept: Key Concept: The law of conservation of mass The law of conservation of mass states that mass is neither created nor states that mass is neither created nor destroyed in a chemical reaction.destroyed in a chemical reaction.

Figure 2


Balancing EquationsBalancing Equations

Key Concept: In order to show that mass is Key Concept: In order to show that mass is conserved during a reaction, conserved during a reaction, a chemical a chemical equation must be balanced.equation must be balanced.

You can balance a chemical equation by You can balance a chemical equation by changing the coefficients, the numbers that changing the coefficients, the numbers that appear before the formulas.appear before the formulas.

No number in front of the formulas is understood No number in front of the formulas is understood to be 1.to be 1.


Balancing EquationsBalancing Equations

Changing the coefficient, changes the amount Changing the coefficient, changes the amount of that reactant or product represented in the of that reactant or product represented in the chemical equation.chemical equation.

Two Steps To Balance EquationsTwo Steps To Balance Equations

1.1. Count the number of atoms of each element Count the number of atoms of each element on each side of the equation.on each side of the equation.

2.2. Change one or more coefficients until the Change one or more coefficients until the equation is balanced.equation is balanced.

Section 7.1


Counting With MolesCounting With Moles**Chemists need practical units for counting **Chemists need practical units for counting things.things.Key Concept: Because chemical reactions often Key Concept: Because chemical reactions often involve large numbers of small particles, involve large numbers of small particles, chemists use a counting unit called the mole to chemists use a counting unit called the mole to measure amounts of a substance.measure amounts of a substance.mole (mol)-an amount of a substance that mole (mol)-an amount of a substance that contains approximately contains approximately 6.02 x 106.02 x 1023 23 particles of particles of that substancethat substance

((Avogadro’s numberAvogadro’s number))


Molar MassMolar Mass

Molar mass-the mass of one mole of a substanceMolar mass-the mass of one mole of a substance

**The molar mass of an element is the same as its **The molar mass of an element is the same as its atomic mass expressed in grams.atomic mass expressed in grams.

Calculate the molar mass of a compound by adding up Calculate the molar mass of a compound by adding up the atomic masses of its component atoms, and then the atomic masses of its component atoms, and then expressing the sum in grams.expressing the sum in grams.

Ex. (NaCl) 1 atom of Cl is 35 grams and one Na atom is Ex. (NaCl) 1 atom of Cl is 35 grams and one Na atom is 23 grams, so the molar mass of NaCl would equal to 58 23 grams, so the molar mass of NaCl would equal to 58 grams; 1 mole of NaCl=58 gramsgrams; 1 mole of NaCl=58 grams


Mole Mass ConversionsMole Mass ConversionsOnce you know the molar mass of a substance, Once you know the molar mass of a substance, you can convert moles of that substance into you can convert moles of that substance into mass, or a mass of that substance into moles.mass, or a mass of that substance into moles.Use the conversion factor 1 mole of the Use the conversion factor 1 mole of the substance equals to that substance’s molar substance equals to that substance’s molar mass.mass.

Ex. 1 mole of COEx. 1 mole of CO22=44.0g of CO=44.0g of CO22; C=12g and ; C=12g and O=16g; 1 atom of C and 2 atoms of OO=16g; 1 atom of C and 2 atoms of O1C=12g and 2Oxy.=32g (12 + 32=44g)1C=12g and 2Oxy.=32g (12 + 32=44g)


Chemical CalculationsChemical Calculations

Chemical equations can be read as Chemical equations can be read as recipesrecipes for for making new substances.making new substances.

Key Concept: In chemical reactions, the mass Key Concept: In chemical reactions, the mass of a reactant or product can be calculated by of a reactant or product can be calculated by using a balanced equation and molar masses of using a balanced equation and molar masses of the reactants and products.the reactants and products.

Calculations With Calculations With Chemical EquationsChemical Equations

Figure 8


Converting Mass to MolesConverting Mass to Moles

Make sure that you have a balanced equation.**Make sure that you have a balanced equation.**

Step 1: Determine how many moles of Step 1: Determine how many moles of substance you are trying to make.substance you are trying to make.

Using Mole RatiosUsing Mole Ratios

Step 2: Use the balanced equation to determine Step 2: Use the balanced equation to determine what number (moles) of a product is given by a what number (moles) of a product is given by a certain number (moles) of a reactant and vice certain number (moles) of a reactant and vice versa.versa.


Converting Moles to MassConverting Moles to Mass

Step 3: Convert the number of moles of the Step 3: Convert the number of moles of the substance to grams by using the molar mass of substance to grams by using the molar mass of the substance.the substance.


Classifying ReactionsClassifying Reactions

Reactions are often classified by the type of Reactions are often classified by the type of reactant or the number of reactants and reactant or the number of reactants and products.products.

Key Concept: Some general types of chemical Key Concept: Some general types of chemical reactions are reactions are synthesis reactionssynthesis reactions, , decomposition decomposition reactionsreactions, , single-replacement reactionssingle-replacement reactions, , double-double-replacement reactionsreplacement reactions, and , and combustion combustion reactions.reactions.


Synthesis ReactionSynthesis Reaction

Def.-a reaction in which Def.-a reaction in which two or more substances two or more substances react to form a single substancereact to form a single substance

A + BA + B→→CC

8 Fe + S8 Fe + S88 ---> 8 FeS ---> 8 FeS


Decomposition ReactionDecomposition Reaction

Def.-a reaction in which a Def.-a reaction in which a compound breaks compound breaks down into two or more simpler substancesdown into two or more simpler substances

ABAB→→A + BA + B

2 H2 H22O ---> 2 HO ---> 2 H22 + O + O22


Single Replacement ReactionSingle Replacement Reaction

Def.-a reaction in which Def.-a reaction in which one element takes the one element takes the place of another element in a compoundplace of another element in a compound

A + BCA + BC→→B + ACB + AC

2 Fe + 6 NaBr --> 2 FeBr2 Fe + 6 NaBr --> 2 FeBr33 + 6 Na + 6 Na


Double Replacement ReactionDouble Replacement Reaction

Def.-a reaction where Def.-a reaction where two different compounds two different compounds exchange positive ions and form two new exchange positive ions and form two new compoundscompounds

AB + CDAB + CD→→AD + CBAD + CB

Pb(NO3)Pb(NO3)22 + 2 KI ---> PbI + 2 KI ---> PbI2 2 + 2 KNO+ 2 KNO33


Combustion ReactionCombustion Reaction

Def.-a reaction in which a Def.-a reaction in which a substance reacts substance reacts rapidly with oxygenrapidly with oxygen, often producing , often producing heat heat and and lightlight

CHCH4 4 + 2O+ 2O22→→COCO22 + 2H + 2H22OO

Common products of combustion are carbon Common products of combustion are carbon dioxide and water.dioxide and water.

Let’s observe a combustion Let’s observe a combustion reaction…reaction…

What happens when a candle burns?What happens when a candle burns?

2 C2 C3030HH6262 + 91 O + 91 O22 --> 60 CO --> 60 CO22 + 62 H + 62 H22O O

We can identify a combustion reaction We can identify a combustion reaction because the products are ____ and ____.because the products are ____ and ____.


Reactions as Electron TransfersReactions as Electron Transfers

Key Concept: The discovery of subatomic Key Concept: The discovery of subatomic particles enable scientists to classify certain particles enable scientists to classify certain chemical reactions as transfers of electrons chemical reactions as transfers of electrons between atoms.between atoms.

Oxidation-reduction reaction-a reaction in which Oxidation-reduction reaction-a reaction in which electrons are transferred from one reactant to electrons are transferred from one reactant to anotheranother


OxidationOxidation

Def.-any process in which Def.-any process in which an element loses an element loses electrons during a chemical reactionelectrons during a chemical reaction

Ex. Ca reacting with O; neutral calcium becomes Ex. Ca reacting with O; neutral calcium becomes an ion with a charge of 2+; calcium will lose an ion with a charge of 2+; calcium will lose those 2 electrons to oxygenthose 2 electrons to oxygen

Ex. Sodium reacts with chlorine; neutral sodium Ex. Sodium reacts with chlorine; neutral sodium becomes an ion with a charge of 1+; sodium will becomes an ion with a charge of 1+; sodium will lose its 1 electron to chlorine lose its 1 electron to chlorine


ReductionReduction

Def.-the process in which Def.-the process in which an element gains an element gains electrons during a chemical reactionelectrons during a chemical reaction

Ex. Ca reacting with oxygen; neutral oxygen Ex. Ca reacting with oxygen; neutral oxygen becomes an ion with a charge of 2-; oxygen will becomes an ion with a charge of 2-; oxygen will gain 2 electrons from calciumgain 2 electrons from calcium

A reactant is said to be reduced if it gains A reactant is said to be reduced if it gains electrons.electrons.


Oxidation-Reduction ReactionsOxidation-Reduction Reactions

Oxidation and reduction Oxidation and reduction always occur togetheralways occur together..

When one element loses electrons, another When one element loses electrons, another element must gain electrons.element must gain electrons.

**Oxidation-reduction reactions **Oxidation-reduction reactions do not always do not always involve complete transfers of electronsinvolve complete transfers of electrons..

Some elements partially lose electrons or Some elements partially lose electrons or partially gain electrons.partially gain electrons.

Chapter 7 Chemical Reactions Section 7.1 Describing Reactions Section 7.2 Types of Reactions.

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Transcript of Chapter 7 Chemical Reactions Section 7.1 Describing Reactions Section 7.2 Types of Reactions.