Accelerated Chemistry

Chapter 8 Notes – Balancing Chemical Equations

Chemical Equations

Problem Set Due day before test: p 290 #8, 10, 11, 15, 25, 26, 27, 35, 37

Chemical equations represent, with symbols and formulas, the reactants and products in a chemical reaction.

reactantsproducts

Chemical equations describe chemical reactions
Requirements for all chemical equations:
  1. must show all reactants and products
  2. formulas must be correct
  3. Law of Conservation of Mass must be satisfied (equation must be balanced)

H2+ Cl22 HCl

yields

Ex1:– decomposition of sodium chloride –– use symbols, heat, etc.

Δ

2NaCl(s)2Na(s)+Cl2(g)

Symbols used in reactions:

  • NaCl(aq) -
  • H2O(l) –
  • g or ↑ =
  •  =
  • ↔ =
  • ΔH =
  • cat = ______(a substance that speeds up a reaction without being used up in the reaction)
  • S or ppt or ↓ = ______(solid - only found on products side)

Significance of a chemical equation: H2 (g)+ Cl2 (g)2 HCl means…

Atoms:

Molecules:

Molarmass: H = 2.0; C = 71.0; HCl = 73.0

Balancing Chemical Equations – a trial and error process

Helpful hints:

1. ______

2. ______

3. ______

4. ______

5. ______

If this doesn’t succeed, try doubling everything (particularly with combustion).

Examples:

__H2O(l)  __ H2(g)+__O2(g)

__(NH4)2CO3 (aq)+__CaCl2(s) __CaCO3(s) +__NH4Cl(aq)

__Al(s) +__Br2(g)__AlBr3(s)

__C2H5OH(g) + __O2(g) __CO2(g) +__H2O(g)

  • ___C3H6(g) + ___ O2(g) ___ CO2(g) + __H2O(g)
  • ____Al(OH)3(aq) + ____ HCl(aq) ____ AlCl3(aq) + ____ H2O(l)

Tin (IV) oxide + Carbon  Tin + Carbon monoxide

Aqueous Iron (III) Chlorate reacts with solid calcium to yield calcium chlorate and solid iron

8.2 Types of Chemical Reactions

5 types

1.

2.

3.

4.

5.

remember - first you’ve got to find the right products, then balance the reaction

1. Synthesis (direct combination) - needs energy to happen (usually heat)

General formula

  • A + B ---> AB

2H2 + O2 → 2H2O

ex.Ba+SMg+Cl2

Al+Cl2Na+O2

2. Decomposition (analysis)- needs energy to happen (usually heat or electricity)

general formula

AB ---> A +B

2H2O → 2H2 + O2

ex.FeCl3HgO

MgSO4. 7 H2O 

(hydrate)

3. Combustion - the reaction of hydrocarbons and oxygen

General Formula

CxH y + O2 CO2 + H2O

  • CH4 + O2 →
  • C3H8 + O2 →
  • C4H10 + O2 →
  • C2H5OH + O2 →

8.3Activity Series of the Elements

Some reactions happen and some don’t!

Assume all synthesis, decomposition, and combustions happen

Not all single or double displacement occur

Single Replacement

Double Replacement

  1. Single replacement - take place in aqueous solutions - need very little energy to happen

Two Types

  • Positive Ions Switch

AB +M  MB+ A

  • Negative Ions Switch

MB +X MX + B

For single replacement, use the Activity Series!

Rules for the single replacement activity series:
  1. Any single element above an element in a compound will ______it.
  2. The top 5 elements react with ______.
  3. Metals above H react with ______(molecules that start with H – not water).
  4. The nonmetal reactivity series is ______...

Examples:

HI(aq) +Mg(s)

AlCl3(aq) +Ca(s)

Ca(s) +HOH(l)

NaCl+ F2

BaS+O2

NaF+Cl2→

Al +H2O→

  1. Double Replacement - aqueous solution - little energy - usually forms one soluble ionic product (aka - aqueous) and either a ppt, water, or a gas that bubbles out of water

General Formula (molecule + molecule)

 AB+CDCB+AD

AgNO3+ NaCl → AgCl + NaNO3

For double replacement reactions, use a Solubility Table!

Rules for double replacement reactions using a solubility table:
  1. If one of the products formed is water, the reaction ______.
  1. If a gas is formed, the reaction ______.
  2. If an insoluble product forms (______), the reaction ______(actually a reaction may happen when two soluble products form, but it doesn’t go to completion and is not directly observable).

Examples-

  • FeCl3+NaOH 
  • H2SO4+NaOH 
  • NH4Cl+NaOH 
  • Na2CrO4 +KCl →
  • FeCl3 + KOH →
  • HCl+NaOH →

Solubility Trends

Cations -very soluble - Na, K, ammonium

very insoluble- Ag, Pb, Hg, transitions

Anions - very soluble - nitrate

for monatomics- FClBr ....

very insoluble -carbonate, hydroxide, phosphate, sulfate

sulfides - decompose

general trend -

Showing Energy Changes in Equations

endothermic -

A + B + heat C ΔH is ______

exothermic -

A + B  C + heat ΔH is ______

Some helpful notes on writing phases in chemical reactions

1. Metals are solids (except Hg, Br)

2. In SR and DR reactions, ______that are ______are always ______.

3. In SR and DR reactions, ______that are ______should have their phases identified using a solubility chart (aqueous vs. precipitate)

4. In S and D reactions, ______compounds are ______.

5. In C reactions, the water, CO2, and O2 are gases. The hydrocarbon is hard to tell, but is usually a liquid after C=6 or higher.

6. Most other ______compounds are ______.

7. Acids (chemicals starting with hydrogen) are always ______.

08 NotesPage 1 of 9

Accelerated Chemistry

Chapter 8 Notes – Balancing Chemical Equations

Activity Series For Metals

Li

K

Ba

Na

Ca

Mg

Al

Zn

Cr

Fe

Ni

Sn

Pb

H

Cu

Hg

Ag

Pt

Au

Activity Series for Halogens

F2

Cl2

Br2

I2

08 NotesPage 1 of 9

Accelerated Chemistry

Chapter 8 Notes – Balancing Chemical Equations

Solubility Table

S – Soluble / I – Insoluble
Ss – Slightly Soluble / D – Decomposes
Bromide / Carbonate / Chloride / Chromate / Fluoride / Hydroxide / Iodide / Nitrate / Phosphate / Sulfate / Sulfide
Aluminum / S / I / S / D / S / I / S / S / I / S / D
Ammonium / S / S / S / S / S / S / S / S / S / S / S
Barium / S / I / S / I / S / Ss / S / S / I / I / D
Calcium / S / I / S / S / S / Ss / S / S / I / Ss / D
Cobalt / S / I / S / S / S / I / S / S / I / S / I
Copper (II) / S / I / S / S / S / I / S / S / I / S / I
Iron (II) / S / I / S / S / S / I / S / S / I / S / I
Iron (III) / S / S / S / S / S / I / S / S / I / S / D
Lead / Ss / I / Ss / I / S / I / Ss / S / I / I / I
Magnesium / S / I / S / S / S / I / S / S / Ss / S / D
Mercury (II) / Ss / I / S / S / S / I / I / S / I / D / I
Nickel / S / I / S / S / S / I / S / S / I / S / I
Potassium / S / S / S / S / S / S / S / S / S / S / S
Silver / I / I / I / I / I / I / I / S / I / Ss / I
Sodium / S / S / S / S / S / S / S / S / S / S / S
Strontium / S / I / S / I / S / Ss / S / S / I / Ss / D
Zinc / S / I / S / S / S / I / S / S / I / S / I

08 NotesPage 1 of 9