3. Reactions and Stoichiometry

Avogadro’s Number

6.022 × 10²³ molecules/mol

Molar mass units

g/mol

Compound

Composed of two or more different elements

Elements

Atoms having the same number of protons (Z)

Molecule

Two or more atoms connected (can form compounds or elements)

Molecular Formula

Gives the exact number of atoms present in a molecule

Empirical Formula

Ratio of atoms of each element present (simplified)

Percent Composition

Percentage by mass of an element in a compound (TRICK: if possible, use empiric formula for calculating)

Are phase changes chemical reactions?

No, they are physical reactions. Chemical reactions require breaking and forming bonds.

7 Chemical Reactions:

1. Synthesis

2. Decomposition

3. Single Displacement

4. Double Displacement

5. Combustion

6. Neutralization (Acid-Base)

7. Oxidation-Reduction (Redox)

Synthesis Reaction (combination)

A + B → C (Ex. 3H₂ + N₂ → 2NH₃)

Decomposition Reaction

C → A + B (Ex. 2KClO₃ (s) → 2KCl (s) + 3O₂ (g)

Is synthesis endothermic or exothermic?

Exothermic because the formation of bonds releases energy

Is decomposition endothermic or exothermic?

Endothermic because breaking bonds requires energy

Displacement Reactions

One element/group replaces another

Single Displacement Reaction

Only one element is replaced (Ex. Fe (s) + CuSO₄ (aq)→ FeSO₄ (aq) + Cu (s))

Double Displacement Reaction

Two groups replace each other

Precipitation Reaction

Specific type of double displacement where a product is insoluble is water and precipitates (Ex. BaCl₂ (aq) + MgSO₄ (aq) → BaSO₄ (s) + MgCl₂ (aq)

Neutralization Reaction

Acid and base react with each other to form a salt and water (Ex. HCl (aq) + NaOH (aq) → NaCl (aq) + H₂O (l)

Combustion Reaction

Any compound that reacts with O₂ to produce gaseous products

Is combustion exothermic or endothermic?

Exothermic because it releases a lot of heat; forming bonds > breaking bonds

Combustion of Hydrocarbons

Results in CO₂ and H₂O gases as products

Oxidation-reduction (Redox)

Involve a transfer of electrons between two species that results in change in oxidation state

Oxidized Species

Gives up electrons (more positive charge)

Reduced Species

Gains electrons (more negative charge)

Rules for Balancing Equations

1. Charges in a compound must be balanced

2. # of reactants = # products

3. Begin with atom present in the least molecules

4. Save diomatomics/elements for last

Anabolic Process

Using smaller molecules to form larger ones; need energy

Catabolic Processes

Breaking down larger molecules into smaller ones; releasing energy

Stoichometry

Calculate the amounts of products or reactants in a molecule

Limiting Reagent

The reactant in the smallest molar (not grams or reaction-based) amount that limits how much product you can make

Calculating Limiting Reagent:

Calculate the moles of product that would form from each reactant

Percent Yield

(Actual/Theoretical) x 100

Polyatomics

NICK the CAMEL ate CLAMS for SUPPER in PHOENIX

Nitrate — Carbonate - Chlorate - Sulfate — Phosphate

Consonants are oxygens, Vowels are negative charges