Chapter 7: Chemical Reactions

Chapter 7, Chapter 16(2-5):

Chemical Reactions

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Chapter 7: Chemical Reactions Bonus Chapter 7: 25, 31, 33, 39, 43, 47, 51, 53, 57, 59, 63, 65, 71, 77, 81, 83, 85, 89, 99 Bonus Chapter 16: 35, 45, 71, 73, 77, 81, 83 Check MasteringChemistry due dates. Evidence of Chemical Reactions: Changes occur in the chemical composition

Color change

Formation of solid

Formation of gas

Emission of light

Change in temperature without externally adding or removing heat. Try this #1: Is boiling water (liquid to gas) a chemical change? Is separation of CuSO4 from sand by dissolving the CuSO4 in water and filtering the sand a chemical change?


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The Chemical Equation: Reactants  Products Phases: solid (s), liquid (l), gas (g), aqueous (aq) Balancing Chemical Equations: Balance the same number of atoms on either side Total charges must also balance on each side Once the formulas are correctly written, add numbers to coefficients (never change a subscript to balance) Process: Write skeletal equation with correct chemical formulas as reactants and products Start with a substance with the most atoms and subscripts If an element occurs in only one compound on both sides, that element should be balanced first. If more than one choice is available, balance metals before nonmetals Balance a free element last, adjust the coefficient on the fee element Remove fractions by multiplying through by the denominator Check Try this #2: Practice balancing the following: O2 (g) 

a)

C3H8 (g) +

CO2 (g) +

b)

Pb(NO3)2 (aq) +

c)

solid zinc is added to hydrochloric acid to produce hydrogen gas and aqueous zinc chloride

d)

carbon dioxide gas and water forms carbonic acid

e)

NH3 (g) +

K2S (aq) 

O2 (g) 

PbS (s)

NO2 (g) +

H2O (l) + KNO3 (aq)

H2O (l)


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Classifying Chemical Reaction Types: (D-D) double displacement (N) neutralization or acid-base, (P) precipitation (R) redox or oxidation-reduction (SR) single replacement (C) combustion (G) gas evolution (Syn) synthesis or combination (D) decomposition Electrolytes in Aqueous Solution: Pure water does not conduct electricity. If charged ions are dissolved in water it will conduct electricity. Strong Electrolytes will dissociate into its ions in an aqueous solution and are written as separated ions in the total and net ionic reactions. Examples: Strong acids, Strong Bases, Soluble salts. Strong Acids: HCl, HBr, HI, HNO3, H2SO4, HClO4, HClO3 Strong Bases: soluble hydroxides from Group IA (not including H) and Group IIA, not including the top two: LiOH, NaOH, KOH, RbOH, Ca(OH)2, Sr(OH)2, Ba(OH)2 Soluble Salts: Ionic compounds that contain cations from Group 1A; Li+, Na+, K+, or NH4+ or the anions NO3-1, ClO4-1, C2H3O2-1 are mostly soluble. Compounds with Cl-1, Br-1, I-1 are soluble except with Ag+, Hg2+2, Pb+2 Compounds with SO4-2 are soluble except Sr+2, Ba+2, Pb+2 or Ca+2.


Chemical Reactions

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Weak Electrolytes will partially dissociate into its ions in an aqueous solution, but are written together in an ionic equation. Weak electrolytes are the weak acids and weak bases such as HC2H3O2 or NH3 Nonelectrolytes will stay together in an aqueous solution. Nonelectrolytes are the insoluble salts [solids], and molecular gases and liquids.

Solubility Rules: memorize the top portion of ions mostly soluble


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Writing Molecular, Ionic, and Net ionic equations: Example: For the double displacement reaction of lead (II) nitrate reacting with potassium iodide.

Whole equation: Balanced Pb(NO3)2 (aq) + 2 KI (aq)  PbI2 (s) + 2 KNO3 (aq) Total ionic equation: Unbalanced Pb+2(aq) + NO3-1(aq) + K+1(aq) + I-1(aq)  PbI2 (s) + K+1(aq) + NO3-1(aq) Identify the spectator ions and leave them out when writing the net ionic eq. Net ionic equation: Unbalanced Pb+2 (aq) +

I-1 (aq)  PbI2 (s)

This is a double displacement reaction and specifically a precipitation reaction. A chemical composition change has occurred. The visible evidence of this change is the formation of yellow solid. Two colorless liquids react to form the new yellow solid PbI 2. Try this #3: Follow the rules above to write the Molecular, Ionic, and Net ionic equations for the reaction of aqueous calcium chloride and aqueous potassium carbonate. Whole equation: Total ionic equation: Identify the spectator ions and leave them out when writing the net ionic eq. Net ionic equation


Chemical Reactions

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Classifying and Predicting Products and Chemical Reactions: The following examples will help you classify the type of reaction and predict the expected products. (D-D) double displacement: AB + CD  AD + CB A double displacement reaction starts with two ionic compounds in which the ions exchange to produce new balanced ionic compounds. Always write the cation before the anion and verify that the net charge of each compound is zero. Ionic compounds may be acid, base, or salt. Oxidation charges do not alter in double displacement reactions so this type will never be a redox reaction. Driving forces for double displacement reactions include formation of a solid (P) Precipitation, Check solubility rules formation of water (N) Neutralization or Acid-Base Reaction formation of a weak electrolyte (WE) (P)

Formation of a new solid in a double displacement reaction when there is no solid on the reactant side is called PRECIPITATION. Ni(NO3)2 (aq) + Na2S (aq)

(N)



NiS (s) +

2 NaNO3 (aq)

DD,P

Formation of water in a double displacement reaction is called NEUTRALIZATION (also known as Acid-Base reaction) 3 KOH (aq) + H3PO4(aq)



K3PO4 (aq) + 3 H2O (l)

DD,N

(WE) Formation of a WEAK ELECTROLYTE, generally a weak acid, produced from a double displacement reaction Al(C2H3O2)3 (aq) + 3 HCl (aq)  AlCl3 (aq) + 3 HC2H3O2 (aq)

DD,WE

(NR) When all ionic products are strong electrolytes, there is NO REACTION. FeBr3 (aq) + 3 LiNO3 (aq)

 3LiBr (aq) + Fe(NO3)3 (aq)

NR


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(G) Gas Evolution: Several common compounds are in the gas phase. You should recognize the following as gases. CO2, SO2, CH4, NH3, H2S, H2, N2, O2, F2, Cl2, NO, NO2 Special cases of (G) Gas Evolution in (DD) Double Displacement: There are three common products that further decompose leading to three products in place of just the two products in a double displacement reaction. They are as follows. NH4OH (aq)

 NH3 (g) + H2O (l)

H2SO3 (aq)

 SO2 (g) + H2O (l)

H2CO3 (aq)

 CO2 (g) + H2O (l)

The double displacement reactions below show examples of the decomposition of one of the ionic products. The driving forces include both formation of water and a gas, because water is formed these can be labeled Neutralization reactions. The last one is DD, N, and P. K2CO3 (aq) + 2HCl (aq) 

H2CO3 (aq) + 2 KCl (aq)

K2CO3 (aq) + 2HCl (aq)  CO2 (g) + H2O (l) + 2 KCl (aq)

Na2SO3 (aq) + 2HCl (aq)

H2SO3 (aq) + 2 NaCl (aq)

Na2SO3 (aq) + 2HCl (aq) SO2 (g) + H2O (l) + 2 NaCl (aq)

(NH4)2SO4 (aq) + Ba(OH)2 (aq)

2 NH4OH (aq) + BaSO4 (s)

(NH4)2SO4 (aq) + Ba(OH)2 (aq) 2 NH3 (g) + 2 H2O (l) + BaSO4 (s) Try this #4: Predict the products and balance for the reaction that geologist use to test for carbonates in rock or mineral samples… HNO3 (aq) +

CaCO3 (s)  (marble)


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(Syn) Synthesis or combination: A + B  AB A synthesis reaction starts with two or more substances and creates a single compound product. The reverse of a synthesis reaction is Decomposition. Remember which elements are diatomic elements: H2, N2, O2, F2, Cl2, Br2, I2. Know the elements in their pure form: gas (red), solid (black), and liquid (blue), by color on the periodic table in the classroom. a) two elements (metal plus nonmetal)  ionic compound. Na (s) + Cl2 (g)  NaCl (s) Balance this

b) metal oxide and water  base (metal hydroxide) BaO (g) + H2O (l)  Ba(OH)2 (aq) c) nonmetal oxide and water  acid CO2 (g) + H2O (l)  H2CO3 (aq) Try this #5: Predict the products and balance… Al (s) + O2 (g)  MgO (s) + H2O (l) 


Chemical Reactions

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(D) Decomposition: AB  A + B A decomposition reaction starts with one reactant and breaks up into two or more substances. The reverse of a decomposition reaction is synthesis. Remember the diatomic elements: H2, N2, O2, F2, Cl2, Br2, I2. a) Water can be broken into its elements by electrolysis

b) ionic compound  two elements (metal plus nonmetal) 2 Fe2O3 (s)  4 Fe (s) + 3 O2 (g) c) metal carbonate  metal oxide and carbon dioxide CaCO3 (s)  CaO (s) + CO2 (g) d) metal bicarbonate  metal carbonate + water + carbon dioxide 2 Al(HCO3)3 (s)  Al2(CO3)3 (s) + 3 H2O (l) + 3 CO2 (g) e) metal connected to halogen with oxygen  metal halide + oxygen Ca(BrO3)2 (s) CaBr2 (s) + 3 O2 (g) f) hydrated salt  anhydrous salt plus water CuSO4.5H2O (s)  CuSO4 (s) + 5 H2O (l)


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Try this #6: Predict the products and balance for the reactions after heating… .

CoCl2 6H2O (s)  KClO3 (s)  NaHCO3 (s) 

(R) Redox or oxidation-reduction: Redox reactions have a transfer of electrons. A way to tell that a redox reaction takes place is to check for element charges and see if they change from reactant side to product side. Some synthesis and decomposition reactions are redox. All single replacement and combustion reactions are redox reactions. (C) Combustion: elements burn with O2 gas to produce oxides, Common products include: CO2, H2O, NO2, SO2. CH4 (g) + 2 O2 (g)  Try this #7: Predict the products and balance C4H10 (l) + O2 (g)  C17H24S (s) + O2 (g)  C12H22O11 (s) + O2 (g)  NH3 (g) + O2 (g) 

CO2 (g) + 2 H2O (l)


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Chapter 16: Oxidation and Reduction Another Redox type reaction: (SR) Single Replacement: A + BC  AC + B or BA + C The more active element will have a partner, less active is alone. Activity series: Au