Chemical equations represent a process in which at least one new substance is formed. Such a process is called a chemical reaction.

2 Na(s) + 2 H₂O(l)  =  2 NaOH(aq) + H₂(g)
 

The Law of Conservation of Mass states that in a chemical process mass is neither created or destroyed.
 

Balancing chemical equations sets them in agreement with the Law of Conservation of Mass.

  Al +     O₂ --->     Al₂O₃

  C₄H₁₀ +     O₂ ---->     CO₂ +      H₂O

  Ga₂O₃ +    H₂SO₄ --->    Ga₂(SO₄)₃ +     H₂O
 

Classes of Chemical Reactions

Synthesis      x + y ---> xy
Decomposition     xy --> x + y
Single Replacement    x^' + xy --> x^'y + x    or     y^' + xy --> xy^' + y
Double Replacement      x^'y^' + xy --> x^'y + xy^'
 

Synthesis Examples

metal oxide + water ---> base

Na₂O + H₂O --> 2 NaOH

MgO + H₂O --> Mg(OH)2

nonmetal oxide + water --> tertiary acid

N2O3 + H₂O --> 2 HNO2

N2O5 + H₂O --> 2 HNO3

Analysis Examples

Metal carbonates when heated yield  oxides + CO₂

CaCO3 -----> CaO + CO₂

Al2(CO3)3 -------> Al₂O₃ + 3 CO₂

Most ammonium salts yield NH₃ + HX when heated.

NH4Cl ---->  NH₃ + HCl

(NH4)2SO4 -----> 2 NH₃ + H₂SO₄

Carbohydrates yield  carbon + water when heated in the absence of oxygen.

C12H22O11 -----> 12 C + 11 H₂O

Single Replacement Examples

Mg + CuSO₄(aq) --> MgSO₄(aq) + Cu

Ag + NaCl(aq) --> no reaction

F₂ + 2 KCl ---> 2 KF + Cl2

Br2 + KCl ---> no reaction

Double Replacement Examples

CaCO3 + 2 HCl(aq) -->  CaCl2 + H₂O + CO₂

NaCl(aq) + AgNO₃(aq) --> NaNO₃(aq) + AgCl(s)

H₂SO₄ + Ca(OH)2 --> CaSO4 + 2 H₂O

SO3 + Ca(OH)2 --> CaSO4 + H₂O

H₂SO₄ + CaO --> CaSO4 + H₂O

SO3 + CaO ---> CaSO4

_{Chemical Equations & the Mole}

                                               2CO + 2NO --> 2CO₂ + N₂
    Molecules                             2         2              2          1

    (amu)                                    2(28) + 2(30)  =  2(44) + (28)

    moles                                    2        2                2         1

   (grams)                                  2(28) + 2(30)  =  2(44) + ( 28)

molecules                                 ?         ?                 ?         ?
 

Stoichiometry; the study of quantitative relationships among products and reactants in chemical reactions:

Stoichiometric solution method:

I. Write the "given" as a fraction.

II. Change the "given" to moles.

III. Use the mole ratio from balanced equation to change mole of "given" to moles of "sought".

IV. Change "sought" to required units.
 

How many grams and how many molecules of carbohydrates are made from the photosynthesis of 62g CO₂ and excess H₂O.

6CO₂ + 6 H₂O --> C₆H₁₂O₆ + 6 O₂
 

62 g CO₂ x 1 mol CO₂ x 1 mol C₆H₁₂O₆ x 180 g C₆H₁₂O₆ = 42 g C₆H₁₂O₆
    1             44g CO₂        6 mol CO2          1 mol C₆H₁₂O₆

The answer to the second question is 1.4 x 10²³ molecules C₆H₁₂O₆. Show the set-up.
 

How many grams of H₂ are required in the Haber Process to react with 49.0 g nitrogen?
N₂(g) + 3 H₂(g) --> 2 NH₃

49.0 g N₂ x 1 mol N₂  x 3 mol H₂ x 2.016 g H₂ = 10.6g H₂
    1            28.01 g N₂   1 mol N₂    1 mol H₂
 

Limiting Reagent Problem

95 g NH₃ reacts with 120 g O₂. What is the limiting reagent? How many grams of excess reagent remain unreacted?

4 NH₃ + 3 O₂ = 2 N₂ + 6 H₂O

95 g NH₃ x 1 mol NH₃ x 2 mol N₂     = 2.8 moles N₂
    1              17 g NH₃     4 mol NH3

120 g O₂ x 1 mol O₂ x 2 mol N₂   = 2.5 mol N₂

O₂ is the limiting reagent because it would produce fewer males of product.
 

How many g NH₃ are needed to use all the limiting reagent, O₂?
 

120 g O₂ x 1 mol O₂ x 4 mol NH₃ x 17 g NH₃ = 85 g NH₃ used
    1            32 g O₂      3 mol O₂       1 mol NH₃

95g ammonia total - 85g ammonia used = 10 g ammonia remain in excess.
 

% yield = actual yield     x 100
              theoretical yield     1
 

In the previous problem if the actual measured yield of N₂ is 2.19 mol, what is the % yield?
 

% yeild= 2.19 mol x 100 = 87.6 = 88% yield
                 2.5mol