Unit 6: Chemical Unit 6: Chemical ReactionsReactions

Chapter 9Chapter 9

Unit 6: Chemical ReactionsUnit 6: Chemical ReactionsI.I. The Nature of Chemical Reactions (9-1)The Nature of Chemical Reactions (9-1) A. Definition: process in which A. Definition: process in which 1 or more 1 or more

substances are converted to new substances are converted to new substances with substances with differentdifferent chemical chemical and physical propertiesand physical properties

B. Common Examples:B. Common Examples: C. ComponentsC. Components

1. 1. ReactantReactant: substance that enters a : substance that enters a chemical reactionchemical reaction2. 2. ProductProduct: substance that is produced : substance that is produced from a chemical reactionfrom a chemical reaction

D. Reason for ReactionsD. Reason for Reactions

* Depends on: * Depends on: valence electronsvalence electrons & & energyenergy

II. Chemical Equations (9-2)II. Chemical Equations (9-2)

A. Definition: A. Definition: sentencessentences that represent that represent reactionsreactions

B. Indicates: what B. Indicates: what substancessubstances are are involved in the reaction & involved in the reaction & how manyhow many

C. Types of EquationsC. Types of Equations

1. Word Equations1. Word Equationsa. Name chemicals involved in the a. Name chemicals involved in the

reactionreaction

b. Only a b. Only a qualitativequalitative description description

Ex: hydrogen + oxygen Ex: hydrogen + oxygen water water(reactants) (yields) (product)(reactants) (yields) (product)

2. Formula Equations2. Formula Equationsa. Gives the formulas of the chemicals a. Gives the formulas of the chemicals

involved and the ratiosinvolved and the ratios

b. Gives a b. Gives a quantitativequantitative description description

Ex: HEx: H22 + O + O22 H H22OO

(reactants) (yields) (product)(reactants) (yields) (product)

** This is not balanced, it must be! Why?** This is not balanced, it must be! Why?

** ** Law of Conservation of Law of Conservation of Mass/AtomsMass/Atoms: in ordinary chemical : in ordinary chemical reactions:reactions:

1.) Total mass of reactants 1.) Total mass of reactants is equal is equal toto total mass of productstotal mass of products

2.) Number of elements for reactants 2.) Number of elements for reactants is is equal toequal to the number of elements for the number of elements for productsproducts

** Atoms are not created nor destroyed, ** Atoms are not created nor destroyed, but they simply but they simply rearrangerearrange. .

** ** CoefficientsCoefficients: numbers in front of the : numbers in front of the formulas in chemical equations that formulas in chemical equations that give the give the ratiosratios of the substances of the substances involved in the reactioninvolved in the reaction

Ex: 2HEx: 2H22 + O + O22 ---> 2H ---> 2H22OO

2 molecules 1 molecule2 molecules 1 molecule 2 molecules2 molecules

oror2 moles2 moles 1 mole 1 mole 2 moles2 moles

Ex: Interpret the following chemical Ex: Interpret the following chemical reactionreaction

2 NaI2 NaI ++ ClCl22 --->---> 2NaCl 2NaCl ++ II22

** Note: What is the difference between ** Note: What is the difference between 2CO and CO2CO and CO22

D. Writing and Balancing Chemical D. Writing and Balancing Chemical EquationsEquations

1. Review: Indicate how many atoms of 1. Review: Indicate how many atoms of each element are present in the each element are present in the following:following:

a.a. 5NH5NH33 ---> --->

b. b. 4Ca(OH)4Ca(OH)22 ---> --->

c.c. 3BaSO3BaSO44 ---> --->

2. Review: Diatomics (H2. Review: Diatomics (H22,O,O22,N,N22,Cl,Cl22,F,F22,Br,Br22,I,I22))

*Exist as a molecule of *Exist as a molecule of 22 atoms when they are atoms when they are by by themselves (natural/elemental form)themselves (natural/elemental form)

3. Steps to writing chemical equations3. Steps to writing chemical equations

a. Write the correct chemical formulas for a. Write the correct chemical formulas for compounds involved in the reactioncompounds involved in the reaction

**AllAll compounds should have a neutral charge- compounds should have a neutral charge- subscriptssubscripts are used to balance the charge on are used to balance the charge on ionic compoundsionic compounds

b. Balance equation according to the law of b. Balance equation according to the law of conservation of atoms – conservation of atoms – coefficientscoefficients are are usedused

c. Indicate the phase of each compoundc. Indicate the phase of each compound((ss) ---> solid) ---> solid((ll) ---> liquid) ---> liquid((gg) ---> gas) ---> gas((aqaq) ---> solid salt dissolved in water) ---> solid salt dissolved in water

d. Show the energy change in the equationd. Show the energy change in the equationEndothermicEndothermic ---> Energy written on left ---> Energy written on left

sidesideExothermicExothermic ---> Energy written on right ---> Energy written on right

sideside

III. Classifying Chemical Reactions (9-3)III. Classifying Chemical Reactions (9-3)

1. Synthesis (S), Composition, or Direct 1. Synthesis (S), Composition, or Direct Combination – Combination – twotwo or more substances or more substances combine to form a more combine to form a more complexcomplex substancesubstance

General Form: General Form: AA + + BB ---> ---> ABAB

Examples: Examples: 2H2 + O2 ---> 2H2O2H2 + O2 ---> 2H2O 4Fe + 3O2 ---> 2Fe2O3 4Fe + 3O2 ---> 2Fe2O3

(rusting)(rusting)

2CO + O2 ---> 2CO22CO + O2 ---> 2CO2

2. Decomposition (D) – a complex 2. Decomposition (D) – a complex substance breaks down to form substance breaks down to form twotwo or or more more simplesimple substances substances

General Form: General Form: ABAB ---> ---> AA + + BB

Examples: 2HExamples: 2H22O ---> 2HO ---> 2H22 + 2O + 2O22

2KClO2KClO33 ---> 2KCl + 3O ---> 2KCl + 3O22

2HgO ---> 2Hg + O2HgO ---> 2Hg + O22

3. Single Replacement (SR) – one element is 3. Single Replacement (SR) – one element is replacedreplaced in a compound by another in a compound by another elementelement

General Form: General Form: AA + + BXBX ---> ---> AXAX + + BB

oror

YY + + BXBX ---> ---> BYBY + + XX

Examples: Fe + CuSOExamples: Fe + CuSO44 ---> FeSO ---> FeSO44 + Cu + Cu

ClCl22 + 2KI ---> 2KCl + I + 2KI ---> 2KCl + I22

Cu + AgNOCu + AgNO33 ---> CuNO ---> CuNO33 + + AgAg

4. Double Replacement (DR) or Ionic – ionic 4. Double Replacement (DR) or Ionic – ionic compounds compounds swapswap partners/pairings partners/pairings

General Form: General Form: ABAB + + XYXY ---> ---> AYAY + + XBXB

Examples: NaCl + AgNOExamples: NaCl + AgNO33 ---> NaNO ---> NaNO33 + AgCl + AgCl

Ba(OH)Ba(OH)22 + NaBr --> BaBr + NaBr --> BaBr22 + 2NaOH + 2NaOH

(NH4)(NH4)22COCO33 + CaCl + CaCl22 --> 2NH --> 2NH44Cl + CaCOCl + CaCO33