Chemical Kinetics and Equilibrium Fundamentals

Chemical Kinetics and Reaction Rates

Factors Influencing Reaction Velocity

• Rate Equation: V = k · [A]^a · [B]^b
• Temperature: The Arrhenius Law: k = k₀ · e^{-E_a / (R · T)}
• Concentration and Pressure: P · V = n · R · T
  P = (n · R · T) / V → n / V = concentration
  P = [X] · R · T
• Standard State and Physical State:
  • Solid: Few collisions result in slow reactions. The level of division is key; more particles mean a greater impact surface.
  • Liquid: Average collision frequency results in average reaction speeds.
  • Gas: Many collisions result in faster reactions.
• Catalysts: Positive catalysts increase speed. Negative catalysts (inhibitors) slow it down. Catalysts do not change thermochemical quantities (ΔH, ΔG, ΔS...), the quantity of product, or the reaction order; they only affect the speed.

Reaction Order and Mathematical Formulas

• Order of Reaction: The exponents of the concentrations in the velocity equation.
• Total Reaction Order: The sum of the exponents of the concentrations in the rate equation.

Additional Formulas

• Reaction Velocity (V_speed): A single value in a reaction where V_speed = V₁ / moles = V₂ / moles = V₃ / moles (for reactants and products).
• Experimental Problems: Solved using ratios (simplifying and substituting to find values).

Energy and Enthalpy Diagrams

• Endothermic: ΔH = H_products - H_reactants > 0
• Exothermic: ΔH = H_products - H_reactants < 0

Chemical Equilibrium Principles

• Irreversible Reactions: Occur in open containers where products leave the system (other than solids or liquids).
• Reversible Reactions: Occur in closed containers with no exchange of matter. These are concurrent processes (formation and destruction) that eventually achieve balance.

Equilibrium Constants and Calculations

• Constant Concentration (K_c): When equilibrium is reached: K_c = ([C]^c · [D]^d) / ([A]^a · [B]^b)
• Gas Phase Constant (K_p): When only gases are involved: K_p = (P_C^c · P_D^d) / (P_A^a · P_B^b)
• Relationship: K_p = K_c · (R · T)^Δn or K_c = K_p · (R · T)^-Δn
• Composition by Volume % (Gas): % = (n_A / n_T) · 100
• Partial Pressures: P_A · V = n_A · R · T; P_A = (n_A / V) · R · T = [A] · R · T
• Mole Fraction (X_A): X_A = n_A / n_T; therefore P_A = X_A · P_T
• Degree of Dissociation (α):
  • α = Moles dissociated / Initial moles
  • α = Dissociated concentration / Initial concentration
  • α = x / C₀

Le Chatelier's Principle and Factors

"The shift of a reversible reaction occurs so as to counteract external disturbances."

• Cooling the reaction favors the exothermic direction.
• Heating the reaction favors the endothermic direction.

Application of Physical States in Calculations

We use solid, liquid, and gaseous states for:

• Concentrations
• Degree of dissociation

We use the gaseous state only for:

• Pressure
• Mole fraction