Stoichiometry and the Mole Concept

• Stoichiometry involves calculating reactants and products in chemical reactions.
• It uses the mole concept to count atoms, ions, and molecules by weighing them.

The Mole Concept

• One mole (mol) equals (6.02 \times 10^{23}) entities, known as Avogadro's number.
• Molar mass is the mass of one mole of a substance, measured in grams per mole (g/mol).
• To calculate molar mass:
• Determine the elements in the compound/molecule.
• Find the number of atoms of each element.
• Obtain the atomic masses from the periodic table.
• Multiply the atomic masses by the number of atoms.
• Sum the total masses to get the molar mass.

Balancing Chemical Reactions

• To balance equations:
• Write the skeleton equation
• List elements and polyatomic ions.
• Ensure the number of atoms for each element is equal on both sides by adjusting coefficients.
• Keep polyatomic ions together.
• Adjust coefficients, not subscripts.
• If faced with even/odd mismatches, try doubling the coefficients.

Types of Chemical Reactions

• Synthesis: Two or more substances combine to form one product, ( A + B \rightarrow AB )
• Example: ( CaO(s) + H_2O(l) \rightarrow Ca(OH)_2(s) )
• Decomposition: One substance breaks into two or more products, ( AB \rightarrow A + B )
• Example: ( NH_4NO_3(s) \rightarrow N_2O(g) + 2H_2O(g) )
• Combustion:
• Hydrocarbon combustion: ( C_xH_y + O_2 \rightarrow CO_2 + H_2O )
• General combustion: ( A + O_2 \rightarrow AO )
• Example: ( CH_4(g) + 2O_2(g) \rightarrow CO_2(g) + 2H_2O(g) )
• Single Replacement: One element replaces another in a compound, ( A + BX \rightarrow AX + B )
• Example: ( 2Li(s) + 2H_2O(l) \rightarrow 2LiOH(aq) + H_2(g) )
• Double Replacement: Exchange of ions between two compounds, ( AX + BY \rightarrow AY + BX )
• Example: ( Ca(OH)_2(aq) + 2HCl(aq) \rightarrow CaCl_2(aq) + 2H_2O(l) )

Net Ionic Equations

• Shows only the particles participating in the reaction.
• Steps:
• Write the balanced molecular equation.
• Write the complete ionic equation.
• Identify and remove spectator ions.
• Write the net ionic equation.
• Types of Reactions:
• Precipitation involves the formation of a solid.
• Neutralization involves the formation of water.
• Gas formation involves the formation of a gaseous product.

Limiting and Excess Reactants

• Limiting Reactant: The reactant that is completely consumed, limiting the amount of product formed.
• Excess Reactant: The reactants left over after the reaction is complete.
• Steps:
• Balance the equation.
• Convert each reactant to moles of the product.
• Identify the limiting reactant.
• Calculate the amount of product formed and the remaining excess reactant.

Percent Yield

• Theoretical Yield: The maximum amount of product that could be formed.
• Actual Yield: The actual amount of product obtained from the reaction.
• Percent Yield: (\frac{\text{Actual Yield}}{\text{Theoretical Yield}} \times 100%)

Empirical and Molecular Formulas

• Empirical Formula: The simplest whole-number ratio of elements in a compound.
• Molecular Formula: The actual number of atoms of each element in a molecule of the compound.
• Steps for Determination:
• Convert percentage to mass.
• Convert mass to moles.
• Divide by the smallest number of moles.
• Multiply to get whole numbers if necessary.

Percent Composition

• Definition: The percent by mass of each element in a compound.
• Formula: [ \text{Percent by Mass} = \frac{\text{Mass of Element in 1 mol of compound}}{\text{Molar Mass of Compound}} \times 100 ]
• Steps:
• Calculate the molar mass of the compound.
• Calculate the mass of each component.
• Determine the percentage of each component.

Learn about stoichiometry, which involves calculating reactants and products in chemical reactions using the mole concept. Stoichiometry uses the mole concept to count atoms, ions, and molecules by weighing them. Understand molar mass and balancing chemical reactions.