CHEM134 Midterm Study Guide

Lectures 1 to 6 on Gases, Intermolecular Forces (IMF), Solutions, Phase Diagrams, Chemical Kinetics, and Chemical Equilibrium.

Kinetic Molecular Theory (KMT)

Describes gas molecules in constant random motion with negligible volume and elastic collisions.

Standard Conditions (STP) for a Gas

Pressure of 1 atm, temperature of 273 K, amount of 1 mol, and volume of 22.4 L.

Ideal Gas Law Equation

PV = nRT, combining Boyle's, Charles's, and Avogadro's laws.

Real Gas Deviation

Occurs when particle volume and intermolecular forces can no longer be ignored.

Electronegativity Periodic Trend

Increases from left to right across a period and from bottom to top up a group.

Intermolecular Forces

Forces of attraction between different molecules.

Intermolecular Forces (Strength Order)

Ion-dipole > hydrogen bonding > dipole-dipole > London dispersion forces.

Ion-dipole

Occurs between an ion and a polar molecule, in which the opposite partial charge of the polar molecule is attracted to the ion.

Hydrogen Bonding

Occurs when hydrogen is covalently bonded to F, O, or N (FON).

Dipole-dipole

Occurs between polar molecules with permanent dipole, in which attraction is between opposite partial charges.

London Dispersion Forces

Universal IMFs caused by temporary electron cloud fluctuations, increasing with polarizability and surface contact.

FONClBrCSIPH

FONClBr - most electronegative atoms will form dipole-dipole with CSIPH - least electronegative atoms.

Effects of Stronger IMFs

Lead to higher viscosity, higher surface tension, and lower vapor pressure.

Miscible Solutions

Two liquids that mix into a homogenous mixture (like dissolves like, so both liquids are polar or nonpolar).

Immiscible Solutions

Two liquids that do not form a homogenous mixture, instead, they form a heterogenous mixture due to how one liquid is polar and the other is nonpolar.

Dynamic Equilibrium in Phase Changes

In a closed container, the rate of evaporation equals the rate of condensation.

Heating Curve Regions

A plot of temperature versus heat, in which sloped regions change phase temperature; flat regions represent constant-temperature phase changes.

Phase Diagram

A plot of pressure versus temperature, in which the plot shows which phase is most stable at a given temperature and pressure, and where phases coexist.

Chemical Kinetics

The study of reaction rates and the factors affecting how quickly reactions occur.

Reaction Rate

The change in concentration of reactants (or products) over time, it describes how quickly reactants disappear or products form and is always a positive value.

Four Factors Affecting Reaction Rate

Reactant concentration, temperature, physical state/surface area, and catalysts.

Stoichiometry - aA + bB —> cC + dD

Rate: -1/a(Δ[A]/Δt) = -1/b(Δ[B]/Δt) = +1/c(Δ[C]/Δt) = +1/d(Δ[D]/Δt)

Average Rate

Measured over a time interval, calculated using 2 points on a graph.

Initial Rate

The instantaneous rate measured at the start of the reaction.

Instantaneous Rate

The reaction rate at a specific moment, determined from the slope of a tangent line.

Rate Law Equation Variables

• aA + bB → products

• n and m are the orders with respect to each reactant

• Reaction is said to be (m + n)^th order overall

Zero-Order Reaction Rate Law

Rate = k; reaction rate does not depend on reactant concentration; Units - Rate = M/s = k.

First-Order Reaction Rate Law

Rate = k[A]; reaction rate is directly proportional to reactant concentration; Units - Rate = M/s, k = 1/s.

Second-Order Reaction Rate Law

Rate = k[A]²; reaction rate is proportional to the square of reactant concentration; Units - Rate = M/s, k = 1/M*s.

Determining the Rate Law with Multiple Reactants

In examining experimental data, differences in reaction rate are compared that differ only in the concentration of one reactant.

Arrhenius Equation Variables

T (temperature - Kelvin); R (gas constant - given in eqn sheet); Ea (activation energy - Joules); A - (frequency factor - depends on k units).

Activation Energy (Ea)

Minimum energy needed to convert reactants into the activated complex or transition state.

Activated Complex

A chemical species with partially broken and partially formed bonds.

Frequency Factor (A)

The number of molecules that begin to form the activated complex in a given period of time.

Exponential Factor in Arrhenius Equation

Between 0 and 1; the fraction of that are successful in surmounting the activation barrier and forming products, it increases with increasing temperature but decreases with increasing activation energy.

Reaction Mechanism

The series of individual chemical steps or reactions (elementary steps) that occurs to produce the overall observed reaction.

Molecularity

The number of reactant particles in an elementary step.

Rate-Determining Step

The slowest step in a reaction mechanism that dictates the overall reaction rate.

Catalysts

Substances that speed up reactions without being consumed by lowering the activation energy of a chemical reaction; consumed in an early mechanism step and then made in a later step.

Enzymes

Protein molecules that catalyze biological reactions, form enzyme-substrate complex.

Reversible Processes

Processes that proceed in both the forward and reverse directions.

Dynamic Equilibrium

The condition wherein the rates of the forward and reverse reactions are equal, however, equal rates do NOT imply equal amounts (concentrations).

Law of Mass Action

The relationship between the chemical equation and the concentrations of reactants and products.

Equilibrium Constant (K) Extreme K Values

When K >> 1 , many more product molecules present than reactant molecules at equilibrium (forward reaction > reverse reaction); When K << 1, many more reactant molecules present than product molecules at equilibrium (reverse reaction > forward reaction).

Equilibruim Constant (K) Moderate K Values

When K > 1, favors product; When K < 1, favors reactants; When K is around 1, neither direction is favored, forward reaction proceeds about halfway.

Different Relationships between K and Chemical Equations

Kforward = 1/Kreverse

K1 = (K2)^n

K3 = K1 x K2

Kc

Concentration equilibrium constant.

Kp

Pressure equilibrium constant.

Are pure liquids and pure solids included in an equilibrium constant expression?

NO, only aqueous solutions and gaseous molecules/atoms are.

Reaction Quotient (Q)

The concentration ratio of the products (raised to the power of their coefficients) to the reactants (raised to the power of their coefficients).

Reaction Quotient (Q) vs. K

If Q > K shifts left; if Q < K shifts right; if Q = K at equilibrium.

Le Châtelier's Principle

A system at equilibrium shifts in a direction that minimizes applied disturbances.

Equilibrium Shifts

Equilibrium shifts away from the side with added chemicals or toward the side with removed chemicals.

Effect of Adding a Gas to a Gas Phase Reaction at Equilibrium

Adding a gaseous reactant increases its partial pressure, equilibrium shifts to the right (towards products), though it does not affect other gases partial pressures.

Effect of Adding an Inert Gas to a Gas Phase Reaction at Equilibrium

Adding an inert gas has no effect on equilibrium.

Effect of Temperature on Exothermic Equilibrium

Adding heat shifts equilibrium left (toward reactants) and decreases the value of K.

Effect of Temperature on Endothermic Equilibrium

Adding heat shifts equilibrium right (toward products) and increases the value of K.

Effect of Catalysts on Equilibrium.

Catalysts have no effect on equilibrium.

ICE Tables

Initial concentration, Change in concentration to reach equilibrium, Equilibrium concentration.

A more electronegative atom is partially ____, while a less electronegative atom is partially ____.

Negative, positive.

Which statement best describes the role of intermolecular forces in determining whether two substances will form a solution?

Solution formation is generally favored when solute-solvent interactions are sufficiently favorable relative to solute-solute and solvent-solvent interactions.

What is a solvent?

A substance that dissolves a solute (the material being dissolved) to form a homogeneous mixture called a solution.

What is a solute?

A substance that dissolves into another substance (called a solvent) to form a homogeneous mixture known as a solution.

What is an example of a solute-solvent interaction?

Salt (solute) dissolving in water (solvent) to form salt water (solution).

What is the main difference between intermediates and catalysts in a reaction mechanism?

Intermediates are a product of an earlier step but a reactant in a later step, meaning that they are consumed through the reaction mechanisms. Catalysts are a reactant of an earlier step but a product of a later step, meaning that they are regenerated through the reaction mechanism. Both essentially “cancel out”, but differ on their chronological order of being a reactant or a product.

Does the equilibrium constant (K) predict the speed of the reaction?

No, it only describes the final composition of the reaction, for example, if the reactants are favored, if the products are favored, or if neither are favored.