L. S. Van Der Sluys Page 1 Reactions Part 1

Chapter 3 & 4: Reactions Part 1

Read: BLB 3.1–3.2; 4.2–4.4

HW: BLB 3:1, 11a, b, e, 13

4:19, 24, 39, 49a, c, e, f, 51b, d

Supplemental: Rxns:1, 2, 6–11

Know: Chapter 3 Reactions

Combustion Decomposition Combination

Chapter 4 Reactions

Exchange reactions (Metathesis) • Formation of a precipitate • Formation of a gas • Formation of a weak or non-electrolyte (neutralization)

Late drop deadline: _______________________ Check out the grade calculator on the Chem110 website or on the Angel Lessons Tab Review chemical nomenclature (SCT #5) Memorize those strong acids & bases (BLB Table 4.2) Bonus deadline for Skill Check Test #10: _________ Missed Exam 1, 2 or 3? Request a sign up form for the Make-up Exam: Covers material from all midterm Exams. You must sign up by completing the request form & giving it to me (download on web).

L. S. Van Der Sluys Page 2 Reactions Part 1

Balancing Equations

Law of conservation of mass: matter cannot be lost in any chemical reaction

L. S. Van Der Sluys Page 3 Reactions Part 1

Balancing Chemical Equations Ch. 3.1

1. Write the unbalanced molecular equation (molecules involved with correct

molecular formulas)

CH4 + O2 ! CO2 + H2O

2. Balance the elements that occur in the fewest chemical formulas on each side.

CH4 + O2 ! CO2 + H2O

focus on C first, then H, then O

CH4 + O2 ! CO2 + H2O

Check: Is it balanced? Add atoms on both sides of the equation.

Use Trial and Error

L. S. Van Der Sluys Page 4 Reactions Part 1

Patterns of reactivity Know how to balance a chemical reaction

1. (Complete) Combustion reactions (Ch. 3.2)

C3H8(g) + 5O2 (g) ! 3CO2 (g) + 4H2O(g)

2. Combination reactions (Chapter 3)

2Mg(s) + O2(l) ! 2MgO(s)

3. Decomposition reactions (Chapter 3)

PbCO3(s) !PbO(s) + CO2(g)

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Patterns of reactivity Continued

4. Exchange reactions (Chapter 4)

a. Precipitation Pb(NO3)2(aq) + 2KI(aq) ! PbI2(s) " + 2KNO3(aq)

b. Neutralization NaOH(aq) + HCl(aq) ! NaCl(aq) + H2O(l)

c. Gas formation 2HCl(aq) + Na2S(aq) ! H2S(g) # + 2NaCl(aq)

5. Single displacement reactions (Redox: Ch. 4)

2Ca(s) + O2(g) ! 2CaO(s)

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Use these patterns of reactivity to write balanced reactions for:

1. The combustion of ethanol (CH3CH2OH) 2. The decomposition of lead carbonate (PbCO3) 3. The combination of nitrogen and hydrogen to form ammonia (NH3) 4. The combination of hydrogen and oxygen to form . . .?

L. S. Van Der Sluys Page 7 Reactions Part 1

Exchange reactions (Double Displacement or Metathesis Rxn)

Exchange positive ions to get products

AD + XZ ! AZ + XD Reactants: Pb(NO3)2 + KI Products: ! PbI2 + KNO3

Now Balance the reaction:

Pb(NO3)2 + KI ! PbI2 + KNO3

Does anything observable happen?

Do you have to do the reaction to know?

L. S. Van Der Sluys Page 8 Reactions Part 1

SOLUBILITY RULES FOR COMMON

IONIC COMPOUNDS IN WATER (based on experimental observations)

1. Almost all ammonium and alkali

metal salts are soluble. 2. Most nitrates, acetates, chlorides,

bromides, and sulfates are soluble.

Exceptions:

silver halides sulfates of Ca, Ba, Pb, Ag

3. Most sulfides, carbonates, phosphates

and hydroxides are insoluble.

Exceptions:

alkali salts ammonium salts (See #1 above.)

Note: if the solubility of a substance is <0.01M it is considered insoluble.

L. S. Van Der Sluys Page 9 Reactions Part 1

Balancing Reactions:

1. write correct molecular

formulas for products and reactants

2. determine the phase (aq, s, l or g) of products

3. determine spectator ions and net ionic rxn

4. balance the mass and charge on both sides

L. S. Van Der Sluys Page 10 Reactions Part 1

Example: Net Ionic Equation for a Precipitation Reaction

Mix silver nitrate and sodium chloride. What happens?

1. Molecular Equation: are any combinations

insoluble? AgNO3 + NaCl ! AgCl + NaNO3

2. Ionic Equation: break apart all SOLUBLE

electrolytes

*Spectator ions: what species don't change

on either side of the arrow? 3. Net Ionic Equation: which species actually

change and react?

L. S. Van Der Sluys Page 11 Reactions Part 1

Metathesis Reactions Require a Driving Force

Given reactants: exchange positive ions

to get products

Driving Forces Include Formation of: 1. 2. 3.

How do you know what is happening? How do you predict the phase of the

products?

Use a Net Ionic Equation

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Acid-Base Reactions (Neutralization reaction)

Acid + base ! salt + water

Molecular Equation HNO3(aq) + KOH(aq) ! KNO3(aq) + H2O

Ionic Equation Spectator ions: Net Ionic Equation

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Hydrogen Ion Transfer

Acids: proton donors Bases: proton acceptors

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Examples: What is the net ionic equation for the reaction between sodium hydroxide and acetic acid? What is the net ionic equation for the reaction between sodium chloride and potassium iodide?

L. S. Van Der Sluys Page 15 Reactions Part 1

5.2 Mixing solutions of K2SO4(aq) and BaCl2(aq) produces an insoluble salt. Which of the following is the correct list of spectator ions for this reaction?

1. K+, SO4

2-, Ba

2+, Cl

-

2. K+, SO4

2-

3. K+, Cl

-

4. Ba2+

, Cl-

5. Ba2+

, SO42-