CHEM II EXAM II

CHAPTER 14: CHEMICAL KINETICS

Reaction Rate

  • Definition: Speed at which a reaction occurs.

  • Units: M/s, mol/hr, g/s, mol/L-hr.

Factors Affecting Reaction Rates

  1. Physical State of Reactants:

    • Gases and liquids react faster (more collisions).

  2. Reactant Concentration:

    • Higher concentration = more collisions = faster reaction.

  3. Temperature:

    • Higher temperature = faster reaction rate.

  4. Catalysts:

    • Speed up reactions without being consumed.

Reaction Rates

  • Rate: Change in concentration over time.

Rate Law

  • Formula: Rate=k[A]^m[B^]n

    • m: order of reaction for A.

    • n: order of reaction for B.

    • Overall Order: m+n

  • Units of k(Rate constant):

    • Zero-order: M/s-or mol L−1s−1

    • First-order: s−1

    • Second-order: L mol−1s−1

    • Third-order: L2mol−2s−

First-Order Reactions

  • Rate Law: Rate=k[A]

  • Units of k: s−1

  • Half-Life:

    • Formula: t1/2=0.693/k

    • Time for reactant concentration to halve.

  • Concentration Equation:
    ln⁡[A]=ln⁡[A]0−kt

Second-Order Reactions

  • Rate Law: Rate=k[A]2

  • Units of k: L mol−1s−1

  • Half-Life:

    • Formula depends on initial concentration:
      t1/2=1/k[A]0

Zero-Order Reactions

  • Rate Law: Constant rate, independent of reactant concentration.

  • Units of k: M/s or mol L−1s−1

Activation Energy (Transition State)

  • Definition: Energy required for reactants to reach the highest energy state (transition state).

  • Arrhenius Equation:
    k=Ae^−Ea/RTk 

    • A: frequency factor.

    • R: gas constant (8.314 J/mol·K).

    • Ea​: activation energy.

    • T: temperature in Kelvin.

  • Logarithmic Form:
    Ln ⁡k=ln⁡ A−Ea/RT

Molecularity

  • Refers to the number of molecules involved in an elementary step.

CHAPTER 15: EQUILIBRIUM CONSTANT

Equilibrium Constant (K)

  • Uses stoichiometric coefficients as exponents in:
    K=[products]^coefficients/[reactants]^coefficients

Magnitude of K

  • K>1: Reaction favors products.

  • K<1: Reaction favors reactants.

Relationship Between KpK_pKp​ and KcK_cKc​

  • For gasses:
    Kp=Kc(RT)^Δn

    • R: gas constant.

    • T: temperature (K).

    • Δn: difference in moles (products - reactants).In this equation, Kp represents the equilibrium constant in terms of partial pressures, while Kc is the equilibrium constant in terms of concentrations.