Gen Chem II Final Exam

Disperson Forces

• Present in all molecules, weakest IMF

• Attractive interactions between the induced partial positive with the induced partial negative dipoles

• Increase in valence electrons, greater surface area means greater boiling point

Dipole-Dipole Forces

• Attractive forces between polar molecules (partial positive and partial negatives), stronger than dispersion forces

• Greater polarity means greater dipole-dipole forces (and boiling/melting points)

• Greater electronegativity, greater dipole-dipole forces

Hydrogen Bonding

• Electrostatic attraction between a partial positive and a partial negative on a N,O,F and has the strongest dipole-dipole interactions

When there is an O-H or N-H functional group or lone pairs on the O and N atoms

When does H bond with H2O (in terms of H-bonding IMF)

When there is an H attached to O,N,F

When does H bond with only itself (in terms of H-bonding IMF)

False: Gas formation is an indicator of a non-homogenous mixture and therefore, not a solution

True or False: When there are bubbles, the gas is a solution

1. Homogenous

2. Uniformly distributed

3. Spontaneous process (meaning no energy, like stirring is required)

Perameters for something to be considered a solution

Exothermic (decrease in internal energy) and increase in the dispersion of matter

When is a solution favored

“Like dissolves like”

1. Solute-solute and solvent-solvent forces must be overcome

2. Solute-solvent forces are established

3. Relative energies determine if dissolution occurs

Describe IMF in solutions

Ionic compounds that are able to dissolve in water and generate a solution with ions, concentration can be measured by conductivity

Electrolytes

Describe weak vs strong electrolytes

Strong: High percentage/lots of dissociation of ions

Weak: Few ions

Molarity (M)

moles / Total volume (L)

Molality (m)

moles of solute / kilograms of solvent

Mole Fraction

moles of A / total moles

What perameter do colligative properties of a solution depend on?

Concentrations of solute

1. Vapor Pressure

2. Freezing Point

3. Boiling Point

4. Osmotic Pressure

Four kinds of colligative properties

• Dissolving a non-volatile substance in something that easily evaporates results in a lower vapor pressure

• Solute molecules decrease the surface area and hinders vaporization and lowers the vapor pressure above the liquid

Describe vapor pressure lowering as a colligative property

• Solute molecules disrupt solvent molecule’s ability to form well ordered crystal structures, so, the freezing point decreases

Describe freezing point depression as a colligative property

• Temperature at which vapor pressure equals atmospheric pressure since vapor pressure is lowered when volatile solutes are present

Describe boiling point elevation as a colligative property

• A diffusion driven transfer of solvent molecules

• As pressure increases, solubility also increases because it increases the particle collisions

Describe osmotic pressure as a colligative property

Van’t Hoff Factor

Number of particles introduced per formula unit

• Solid in liquid: direct relationship

• Gas in liquid: indirect relationship, higher temperatures gives gas molecules more of a chance to escape the liquid

Describe temperature and solubility

Reaction Rate

Change in concentration of a reactant or product with time (M/s) (+ also think loss of reactants over time)

Proportional

The rate of a reaction is proportional/disproportional to the concentration of the reactants

Proportionality/rate constant (k)

Proportionality constant that does not depend on the concentration

Zero order reactions (integrated)

[A]t = =kt + [A]0

First order reactions (integrated)

ln([A]t/[A]0) = -kt

Second order reaction (integrated)

1/[A]t = kt + 1/[A]0

Graph of zero order reaction

[A] vs t
- negative k value (slope)

Graph of first order reaction

ln[A] vs t
- Negative k value (slope)

Graph of second order reaction

1/[A] vs t
- Positive k value (slope)

Zero order half life

t(1/2)=1/k x [A]/2

First order half life

t(1/2) = 1/k x 0.693

Second order half life

t(1/2) = 1/k x 1/[A]

Concentration
Temperature
Activation energy
Catalysts

Four factors that affect reaction rates

Increasing concentrations of reactants, increase rates of reaction

How does concentration affect reaction rates

Increasing temperatures, increases the rate of reactions

How does temperature affect reaction rates

More activation energy required means a lower reaction rate (indirect relationship)

How does activation affect reaction rates

Catalysts lower the activation energy so, this would increase the reaction rate

How does a catalyst affect reaction rates

Arrhenius Equation

Equation that describes the dependence of the rate constant (k) on temperature and on the activation energy

• As temperature increase, EF will also increase (same as when temperature decreases, EF will also decrease)

• As activation energy decrease, EF will increase

Describe the mathematical relationships in the exponential factor of the Arrhenius Equation

Transition State

A temporary species formed by the reactant molecules as a result of their collision before they form a product

Exothermic

On a reaction energy diagram, when the energy of the products are negative in comparison to the reactants, is this exothermic or endothermic?

Endothermic

On a reaction energy diagram, when the energy of the products are postive in comparison to the reactants, is this exothermic or endothermic?

Reaction mechanism

The sequence of elementary steps that leads to product formation

Elementary Step

Process that occurs in a single event or step - simple reactions that are part of a larger series.

INtermediate

A compound that is both produced and consumed in elementary steps, never show up in the overall balanced chemical equation

Molecularity

Number of molecules reacting in an elementary step

• Each peak is associated with an activation energy so, this equals to the number of steps in the mechanism

• Intermediates are shown in the valleys

On a reaction energy diagram, what do the peaks and valley’s describe?

Equilibrium

State at which the forward and reverse reactions proceed at the same rate; concentrations of reactants and products remain the same

Products > Reactants

If K>1 at equilibrium

Products = Reactants

If K=1 at equilbrium

Products < Reactants

If K<1 at equilibrium

Le Chatelier’s Principle

If an external stress is applied to a system (like change in concentration, pressure, volume, temperature) at equilibrium, the system adjusts in such a ways that the stress is partially offset as the system reaches a new equilibrium position

• If an amount of taken away, the system will shift in the direction to make more of it

• Is an amount is added, the system will shift in the direction to “make less” (or not make anymore)

Describe what happens when the concentration is changed at equilibrium

• Increasing the pressure will lead the system to shift in favor of the side that has less moles

• Decreasing the pressure will lead the system to shift in favor of the side that has more moles

Describe what happens when the pressure is changed at equilibrium

• “Adding” heat as a reactant describes an endothermic process

• “Producing” heat as a product describes an exothermic process

Describe what happens when the temperature is changed at equilibrium

Bronsted-Lowry acid

Donating a proton

Bronsted-Lowry base

Accepting a proton

Conjugate base

One fewer H atom and one more negative charge than the formula of the corresponding acid

Conjugate acid

One more H atom and one more positive charge than the formula of the corresponding acid

Autoionization of Water

Kw = 1×10^-14 at 25ºC

Strong acid

Acid that completely ionizes in water

Weak acid

Acid that partially ionizes in water

Strong base

Base that completely dissociates in water

Weak base

Base that partially dissociates in water

Stronger weak acid

Larger Ka values means…?

Weaker weak acid

Smaller Ka values means…"?

Because they completely dissociate at equilibrium

Why don’t strong acids have Ka values?

Solubility Equilibrium Expression

Equilibrium expression that describes how soluble the compound is, typically expressed in terms of only the products

The compound is not very soluble

What does this tell us about the solubility of the ion is the Ksp value is very small?

Molar Solubility

Number of moles of solute per 1L of a saturated solution

AA precipitate forms (and if there are two possible precipitates, the one with the smallest Ksp precipitates first)

Q > Ksp

Donate electrons

Lewis Acids

Accept electrons

Lewis Bases

True! Think about the exchange in protons…

True or False: Lewis Bases are also Bronstead-Lowry Bases…and Lewis Acids are also Bronstead-Lowry Acids

Exothermic

ΔHrxn < 0

Endothermic

ΔHrxn > 0

Entropy (S)

The measure of different ways a system can disperse its energy (essentially, the amount of “chaos”)

Entropy increases

Will entropy increase or decrease if the temperature increases and it is exothermic

Always spontaneous

ΔH is negative, ΔS is positive

Spontaneous at low temperatures

ΔH and ΔS are both negative

Spontaneous at high temperatures

ΔH is positive, ΔS is positive

Never spontaneous

ΔH is positive, ΔS is negative

Gibbs Free Energy

Thermodynamic value that describes the total energy change for the system

Spontaneous

When Gibb’s Free Energy is negative

Non-spontaneous

When Gibb’s Free Energy is positive

Spontaneity of a Reaction

A reaction that, once started, will proceed on its own without needing continuous external energy input. However, this doesn’t mean it will proceed quickly or explosively.

Standard-state conditions of Gibb’s Free Energy

A reaction occurring at 25ºC, 1atm of pressure, and 1M concentration

Nonstandard-state conditions of Gibb’s Free Energy

A reaction that is more representative of conditions we are usually dealing with (changes in temperature and varying concentrations)

Anode to cathode: since the anode is the element being oxidized, it is losing electrons so the cathode/reduced element is willing to accept it which generates electricity

In an electrochemical cell, which way do the electrons flow and why?

Standard reduction potential, Eº

The voltage associated with a reduction reaction at an electrode when all solutes are 1M and all gases are at 1 atm

Standard reduction potentials of the reduction half-reactions describing the redox reaction

What do standard cell potentials depend on?

True

True or False: Standard reduction potentials are intensive properties so they are independent of the stoichiometry applied with balancing a redox reaction

The more positive value = Eºcathode

How to determine the Eºcathode value when given the voltage for each half-reaction

Spontaneous

Eºcell > 0

Non-spontaneous

Eºcell < 0

Working with nuclear reactions/chemistry

Elements in the form of isotopes, elementary particles, release/absorptions of large amounts of energy, and reaction rates not being affected external factors are typical of what kind of reaction…

+2

Charge of an alpha particle

-1

Charge of a beta particle