Equilibrium, Acids, Bases and pH

• Increasing the concentration of reactants shifts equilibrium to the right, towards products.
• Increasing temperature shifts equilibrium in the endothermic direction.
• Increasing pressure shifts equilibrium to the side with fewer gas molecules.

Reversible Reactions

• A reversible reaction can proceed in both forward and reverse directions.
• These reactions achieve dynamic equilibrium, where forward and reverse reaction rates are equal.

Bronsted Acids and Bases

• A Bronsted acid donates a proton (H+).
• A Bronsted base accepts a proton (H+).
• In the reaction HCl + H2O -> H3O+ + Cl-, HCl is the Bronsted acid (proton donor), and H2O is the Bronsted base (proton acceptor).

Definition of pH

• pH measures the acidity or basicity of a solution.
• pH is defined as: pH = -log [H+]
• pH < 7 indicates an acidic solution.
• pH = 7 indicates a neutral solution.
• pH > 7 indicates a basic solution.

Galvanic Cell

• A galvanic cell (or voltaic cell) is an electrochemical cell that converts chemical energy into electrical energy via a spontaneous redox reaction.
• It has two electrodes (anode and cathode) connected by a salt bridge.
• At the anode (oxidation), electrons are lost.
• At the cathode (reduction), electrons are gained.
• Electrons flow from anode to cathode, producing electrical current.

Reaction Kinetics

• For the reaction $A + B \rightarrow 2C + D$, the reaction rate is $-r_A = \dfrac{moles \ A \ disappearing}{(volume) (time)}$.
• The reaction rate is expressed as −rA = f(T, CA, CB,...)
• The reaction rate can be described as −rA = k f(CA, CB,...) where k is the specific reaction rate.
• The specific reaction rate, k, depends only on temperature.

Rate Laws

Elementary Rate Law

• For $A + B \rightarrow C$, the rate law is $-r_A = kC_A C_B$.
• For $2A + B \rightarrow C$, the rate law is $-r_A = kC^2_A C_B$

Non-Elementary Rate Law

• For $2A + B \rightarrow C$, the rate law can be $-r_A = \dfrac{kC_A C_B}{1 + K_A C_A}$.

Temperature Dependence

Arrhenius Equation

• The Arrhenius equation describes the temperature dependence of the specific reaction rate: $k = Ae^{-\frac{E}{RT}}$
  • k = specific reaction rate (units depend on rate law)
  • A = frequency factor (units depend on rate law)
  • E = activation energy (cal/mol, J/mol)
  • R = gas constant (1.987 cal/mol K, 8.314 J/mol K)
  • T = absolute temperature (K)

Activation Energy

• Activation energy is the necessary energy for a chemical reaction to occur.

Frequency Factor

• The frequency factor represents the collision rate of molecules per unit time.

Rule of Thumb

• Reaction rate doubles for every 10°C increase in temperature.

Reaction Orders

• For a single reaction $A \rightarrow Products$, the rate is $-r_A = -\dfrac{dC_A}{dt} = kC_A^n$.

Zero Order

• For n = 0, $-r_A = k$.
• The concentration is $C_A = C_{A0} - kt$.
• The time is $t = \dfrac{C_{A0}}{k}$.

First Order

• For n = 1, $-r_A = kC_A$.
• The concentration is $C_A = C_{A0}e^{-kt}$.
• The time is $t = \dfrac{ln(\frac{C_{A0}}{C_A})}{k}$
• $t_{1/2} = \dfrac{ln(2)}{k}$

Second Order

• For n = 2, $-r_A = kC_A^2$.
• $\dfrac{1}{C_A} - \dfrac{1}{C_{A0}} = kt$.
• $t = \dfrac{C_A - C_{A0}}{kC_AC_{A0}}$.
• $t_{1/2} = \dfrac{1}{kC_{A0}}$.

Multiple Reactions

• Multiple reactions include Series Reactions and Parallel Reactions.

Series Reactions

• Series reactions are consecutive, such as $A \rightarrow B \rightarrow C$.

Parallel Reactions

• Parallel reactions are competing, such as $A \rightarrow B$ and $A \rightarrow C$.