Chemical Kinetics Quiz

Chemical Kinetics

• Chemical Kinetics studies the rates of chemical reactions.
• Rate of reaction: The change in concentration of reactant or product per unit time.
• Elementary reaction: A reaction that occurs in a single step.
• Complex reaction: A reaction that occurs in more than one step.
• Rate laws describe the relationship between the rate of a reaction and the concentration of reactants.
• Order of reaction is determined experimentally, and represents the sum of the exponents of the concentration terms in the rate law.
• Rate constant (k) is a proportionality constant relating the rate of the reaction to the reactant concentrations.
• The units of the rate constant depend on the overall order of the reaction.
• Measuring reaction rates is important for understanding kinetics.

Rate of Reaction

• Rate of reaction is proportional to active masses of reactants raised to their stoichiometric coefficients.
• Rate law is determined experimentally.
• Rate = k[A]^m[B]ⁿ
• k = rate constant
• m and n = orders with respect to A and B respectively

Zero Order Reaction

• Rate of reaction is independent of reactant concentrations.
• Rate = k

First Order Reaction

• Rate is directly proportional to the concentration of one reactant.
• Rate = k[A]

Half-life (t_1/2)

• Time required for the concentration of a reactant to decrease to half its initial value.
• First Order: t_1/2 = 0.693 / k
• Zero Order: t_1/2 = [A]₀ / 2k

Collision Theory

• Chemical reactions occur when reactant molecules collide with sufficient energy and proper orientation.
• Rate depends on: Collision frequency, Fraction of collisions with sufficient energy, Proper orientation of colliding molecules

Factors Affecting Reaction Rate

• Temperature: Increased temperature increases the rate.
• Concentration: Increased concentration increases the rate.
• Catalysts: Catalysts increase the rate without being consumed.
• Surface area: Increased surface area increases the rate (for heterogeneous reactions).

Arrhenius Equation

• Relates the rate constant (k) to temperature (T) and activation energy (Ea).
• k = Ae^-Ea/RT
• A = pre-exponential factor
• R = ideal gas constant

Catalysts

• Substances that increase the rate of a reaction without being consumed.
• Provide an alternative reaction pathway with a lower activation energy.

Molecularity

• Total number of reactant molecules participating in a single step of a reaction.
• For elementary reactions, molecularity corresponds to order.

Solutions

• Homogeneous mixtures of two or more components.
• Components: Solute (dissolved substance) and solvent (the dissolving medium).

Concentration of Solution

• Molarity (M): Moles of solute per liter of solution.
• Molality (m): Moles of solute per kilogram of solvent.
• Mole fraction (X): The ratio of moles of a component to the total moles of solution.

Colligative Properties

• Properties of solutions that depend only on the number of solute particles, not on their identity.
• Examples: Vapor pressure lowering, boiling point elevation, freezing point depression, osmotic pressure.

Colligative Properties: Vapor Pressure Lowering

• Vapor pressure of a solution is lower than the vapor pressure of the pure solvent.
• Vapor pressure lowering is directly proportional to the mole fraction of the solute.
• Ratio of vapor pressure of the solution to that of the pure solvent is equal to mole fraction of the solute,

Colligative Properties: Boiling Point Elevation

• Boiling point of a solution is higher than the boiling point of the pure solvent.
• Boiling point elevation is directly proportional to the molality of the solute.

Colligative Properties: Freezing Point Depression

• Freezing point of a solution is lower than the freezing point of the pure solvent.
• Freezing point depression is directly proportional to the molality of the solute.

Colligative Properties: Osmotic Pressure

• Osmotic pressure is the pressure required to prevent the flow of solvent across a semipermeable membrane.
• Osmotic pressure is directly proportional to the molarity of the solute.
• Increased concentration, higher osmotic pressure.

Electrochemistry

• The branch of chemistry that deals with the relationship between electricity and chemical reactions.
• Electrolytes: Substances that conduct electricity in solution or molten state.
• Non-electrolytes: Substances that do not conduct electricity in solution or molten state.
• Types of electrolytes: Strong and weak.
• Conductivity and Conductance: The ability of a solution to conduct electricity.
• Specific conductance (K): Conductance of a solution of 1cm length and 1 sq. cm cross-section area
• Molar Conductivity (∧m): Conductance of a solution in which the volume contains one mole of electrolyte.
• Kohlrausch's Law: At infinite dilution, the molar conductivity of an electrolyte is the sum of the ionic conductivities of the cation and the anion.

Electrolysis

• Electrochemical process where an electric current is passed through an ionic compound to cause a chemical reaction.
• Faraday's Laws: Relationship between amount of substance deposited/liberated at an electrode and quantity of charge passed.
• Electrolytic Cells: Cell in which electrolysis is carried out.
• Batteries: Electrochemical devices that convert chemical energy into electrical energy.
• Primary cells (non-rechargeable) and Secondary cells (rechargeable).

Electrode Potentials

• Potential difference between electrode and electrolyte.
• Standard Electrode Potential (E⁰): Electrode potential under standard conditions.
• Nernst Equation: Relates electrode potential to concentration of ion under nonstandard conditions.

Oxidation and Reduction

• Oxidation: Loss of electrons.
• Reduction: Gain of electrons.
• Redox reactions are coupled reactions, oxidation taking place at one electrode, and reduction at the other electrode.