Unit 11 Stoichiometry

I. Definitions

  1. Pure Substances: can be classified as either elements or compounds
  2. Elements: the simplest kinds of substances, cannot be broken down by ordinary chemical means
  3. Compounds: substances made up of two or more elements that are chemically combined in a fixed proportion
  4. Symbols: abbreviations for elements (the first letter is always capital and the second letter (if applicable) is always lower case
  5. Formula: a statement informing us of the identity of the elements present in a substance and the ratios in which they are found
  6. Empirical Formula: a formula showing the simplest ratio of the elements in a compound (Ionic formulas are usually empirical)
  7. Molecular Formula: a formula that indicates the number of atoms that are present in the smallest particle that has the chemical properties of a substance
  8. Binary Compounds: a compound made up of only two elements
  9. Ternary Compounds: a compound made up of more than two elements
  10. Oxidation Number: when an element becomes an ion (loses or gains electrons) the oxidation number is the same as the charge.
  11. Reactant: one of the substances consumed chemical reaction , a starting substance (on the left of the arrow)
  12. Product: what is produced as a result of a chemical reaction (right side of arrow)
  13. Stoichiometry: the study of the quantitative aspects of formulas and equations (how much of each substance is used or produced)
  14. Synthesis: a type of reaction where a more complex compound is made from two or more simpler substances
  15. Decomposition: a chemical change in which a substance breaks down to form two or more simpler substances
  16. Single Replacement: when an element reacts with a compound to produce a different element and compound
  17. Double Replacement: when two compounds react to form two different compounds
II. Chemical Formulas
  1. Writing Chemical Formulas

a)Criss-Cross Method: For each element present, write the oxidation state (found in the top right corner of the periodic table). Next, criss-cross the numbers ignoring the sign.

Example: sodium + chlorine

1)sodium + oxygen

2)calcium + chlorine

b)Polyatomic Ions (Table E): Two or more atoms that are chemically combined and possess a net electric charge.

  1. Naming Chemical Formulas

a)Binary Compounds: composed of two elements

  1. Metal + Nonmetal: the metallic element is named and written first (it keeps its name), the nonmetallic element is second and its ending is changed to –ide.
  2. Nonmetal + Nonmetal: the less electronegative element is named and written first (it keeps its name), the other element is second and its ending is changed to –ide. Prefixes are used to indicate the number of atoms of each nonmetal.
  3. Prefixes for nonmetals: 1 mono-

2 di-

3 tri-

4 tetra-

b)Ternary Compounds: consist of three elements

c)Stock System: In naming compounds of metals that have more than one oxidation number, the name of the metal is followed by a Roman numeral that represents the oxidation number in that compound.

Example: chromium III bromide CrBr3

Example: nitrogen IV oxide NO2

  1. Labeling a chemical equation:

2H2 (g) + 02(g) ----2H2O(g)

Coefficient Phases of matterYields

ReactantsProducts

(Yields)

Phases of matter:

(g) gas

(l) liquid

(s) solid

(aq) aqueous (dissolved in water)

You might see:

 Yield

Rex must be heated

 Reversible rex

IV: Energy:

  • 2 types of reactions dealing with energy
  1. Endothermic:

(inside) (heat)

  • Chemical reactions that absorb energy or heat
  • It feels cold to the touch
  • You’ll see energy added on the left hand side of the equations

i.e. ice packs

  1. Exothermic

(outside) (heat)

  • Chemical reactions that release energy
  • They feel hot to the touch
  • You’ll see energy on the right hand side of the equations

i.e. heat packs

V: Types of reactions

  1. Synthesis:
  • A combination of 2 or more substances to form a compound
  • A + B  C
  • i.e. 2 Na (l) + Cl2 (g)  NaCl
  1. Decomposition:
  • Opposite of synthesis
  • AB  A + B
  • i.e. 2 H2O (l)  2 H2 (g) + O2 (g)
  1. Single Replacement:
  • One element takes the place of another
  • A + BC  AB + C
  • i.e. Cl2(aq) + 2 KBr (aq)  2KCl (aq) + Br2 (aq)
  1. Double Replacement:
  • Elements in compounds change partners
  • AB + CD  AC + BD
  • i.e.Pb(NO3)2(aq) + 2KI(aq)PbI2(s)+2KNO3(aq)

Evidence of a chemical reaction: How do we know a rex has taken place?

release of a gas (baking a cake)

color changes (leaves in the fall)

formation of a precipitate (solid substance formed from solutions)

changes in heat and light (candle burning)

Practice: Classify these reactions

1.P4 + 5O2P4O10______

2.CH4 + 2O2 CO2 + 2H20______

3.2Fe + 3Cl2 2FeCl3______

4.3AgNO3 + AlCl3 3AgCl + Al(NO3)3 ______

5.2N2 + 5O2 2 N2O5______

6.2KClO3 2KCl + 3O2______

7.2HCl + Mg  MgCl2 + H2______

8.CaCO3  CaO + CO2______

9.2HCl + K2CO3  2KCl + H2CO3______

10.2Al + 3Br2 2AlBr3______