General Chemistry
Stoichiometry, Gas Laws, and Chemical Reactions
Stoichiometry
The Mole Concept
- Avogadro's Number: 6.022 × 10²³ particles/mol
- Molar Mass: Mass of 1 mole (g/mol) = atomic/molecular weight
- Moles: n = mass / molar mass
Stoichiometry Steps
- Balance the chemical equation
- Convert given quantity to moles
- Use mole ratio from balanced equation
- Convert to desired unit
Limiting Reactant
The reactant that is completely consumed first, limiting the amount of product formed. Compare mole ratios to find which runs out first.
Percent Yield
% Yield = (Actual Yield / Theoretical Yield) × 100
Gas Laws
Boyle's Law
P₁V₁ = P₂V₂
At constant T: P and V are inversely proportional
Charles's Law
V₁/T₁ = V₂/T₂
At constant P: V and T are directly proportional
Gay-Lussac's Law
P₁/T₁ = P₂/T₂
At constant V: P and T are directly proportional
Combined Gas Law
P₁V₁/T₁ = P₂V₂/T₂
Combines all three laws
Ideal Gas Law
PV = nRT
- P = Pressure (atm)
- V = Volume (L)
- n = moles
- R = 0.0821 L·atm/(mol·K)
- T = Temperature (K)
STP (Standard Temperature and Pressure)
T = 273.15 K (0°C), P = 1 atm. At STP, 1 mole of gas = 22.4 L
Solutions
Concentration Units
- Molarity (M): mol solute / L solution
- Molality (m): mol solute / kg solvent
- % by mass: (mass solute / mass solution) × 100
- ppm: parts per million (mg/L)
Dilution
M₁V₁ = M₂V₂
Moles of solute remain constant during dilution
Colligative Properties
Properties that depend on the number of solute particles:
- Boiling point elevation: ΔTb = Kb × m × i
- Freezing point depression: ΔTf = Kf × m × i
- Osmotic pressure: π = MRT
Thermochemistry
Key Concepts
- Enthalpy (H): Heat content at constant pressure
- ΔH < 0: Exothermic (releases heat)
- ΔH > 0: Endothermic (absorbs heat)
Heat Calculations
q = mcΔT
- q = heat (J)
- m = mass (g)
- c = specific heat capacity (J/g·°C)
- ΔT = change in temperature
Hess's Law
The total enthalpy change for a reaction is the same regardless of the pathway taken. Add individual ΔH values for each step.
Chemical Equilibrium
Equilibrium Constant (K)
For reaction: aA + bB ⇌ cC + dD
K = [C]^c[D]^d / [A]^a[B]^b
Products over reactants, raised to stoichiometric coefficients
Le Chatelier's Principle
When stress is applied to a system at equilibrium, the system shifts to relieve the stress.
- Add reactant: Shifts right (toward products)
- Add product: Shifts left (toward reactants)
- Increase pressure: Shifts toward fewer moles of gas
- Increase temperature: Shifts in endothermic direction
Reaction Quotient (Q)
Same formula as K, but using current concentrations (not equilibrium).
- Q < K: Reaction proceeds forward
- Q > K: Reaction proceeds reverse
- Q = K: At equilibrium