Exam 2 Flashcards
What is an Intramolecular Force?
They are chemical bonds; hold together the atoms within a molecule
What is an Intermolecular Force?
Attractive forces between molecules; responsible for bulk properties (e.g. boiling point, melting point)
What are Dipole-Dipole Interactions?
Attractive forces between polar molecules
What are Ion-Dipole Forces?
Attractive force between an ion and a neutral molecule that has a dipole (e.g. CsCl in H2O)
What are Dipole-Induced Dipole interactions?
Occurs when nonpolar molecules are mixed with polar molecules. It results when a polar molecule induces a dipole in a nonpolar molecule by disturbing the arrangement of electrons in the nonpolar molecule
What are Ion-Induced Dipole interactions?
Occurs when nonpolar molecules are mixed with ions. It results when the ion induces a dipole in the nonpolar molecule by disturbing the arrangement of electrons in the nonpolar molecule
What are Dispersion forces? (aka Van der Waals, London)
Attractive forces that exist between all molecules or atoms/ions. They play an important role in the attraction between nonpolar substances (e.g. noble gases)
What is polarizability?
The ease with which the electron distribution around an atom or molecule can be distorted; as the volume of the electron cloud increases, the polarizability increases
Do larger or smaller molecules have higher dispersion forces?
Large and heavier atoms and molecules exhibit stronger dispersion forces than smaller and lighter ones
For molecules containing the same elements, do dispersion forces increase or decrease with an increased number of atoms?
Increase
Does n-pentane or neopentane have a higher boiling point?
N-pentane has a higher boiling point. N-pentane (liquid) is chainlike -> larger surface area -> stronger dispersion forces -> higher boiling point
Neopentane (gas) is spherical shaped (compact) -> small surface area -> weaker dispersion forces -> lower boiling point
What are Hydrogen Bonds?
Attractive force between a hydrogen atom covalently bonded to a F, O, or N atom and another very electronegative atom
List the Intermolecular Forces from strongest to weakest.
Ion-dipole > H-bond > Dipole-Dipole > Ion-induce dipole > Dipole-induced dipole > Dispersion
Define Cohesive Forces
Intermolecular forces between like molecules
Define Adhesive Forces
Intermolecular forces between unlike molecules
When do concave shaped meniscus occur?
When adhesive > cohesive; when the liquid is more attracted to the wall than its neighbors (e.g. water)
When do convex shaped meniscus occur?
When cohesive > adhesive; the cohesive force of the liquid is stronger than the adhesive force of the liquid to the wall (e.g. Mercury, Hg)
What is viscosity?
The measure of a fluid’s resistance to flow; decreases as temperature increases; liquids with stronger IMF’s have higher viscosity
What are the factors that affect the rate of evaporation?
Surface area, temperature, and strength of IMF’s; high surface area -> high rate of evaporation -> high vapor pressure
How does temperature affect evaporation?
Increased temperature = greater evaporation
How do Intermolecular Forces affect evaporation?
Weak IMF’s -> high rate of evaporation -> high vapor pressure
How does temperature affect vapor pressure?
VP increases as temperature increases
How do IMF’s affect vapor pressure?
VP decreases as the strength of IMF’s increase
How are vapor pressure and volatility related?
Increased vapor pressure = more volatile
Equation for the enthalpy of vaporization at a given temperature (delta Hvap)
ln p = ( /\Hvap / R) * (1/T) + C
Equation for the enthalpy of vaporization at two different temperatures
ln (P2/P1) = ( - /\ Hvap / R) x [ (1/T2) - (1/T1)]
What is the equation for the molar heat of fusion?
q = n x delta Hfus (where q=heat or energy and n=#ofmols)
What is the equation for the molar heat of vaporization?
q = n x delta Hvap
What is the triple point?
The point at which all three phases are in equilibrium. Below the triple point the substance cannot exist in the liquid state
What is the critical point?
It is where the critical temperature and the critical pressure meet. Above the critical point, it is no longer possible to distinguish between the gas and liquid phases (aka supercritical fluid)
Why is solid CO2 known as “dry ice”?
Because the triple point is well above atmospheric pressure. You cannot have liquid carbon dioxide at pressures less that 5.11 atm. So at 1 atm carbon dioxide will go from a solid to a gas (no liquid stage)
Phase going from a solid to a gas is known as?
Sublimation
Phase going from a gas to a solid is known as?
Deposition
For liquids, as the strength of Intermolecular Forces increase, what does the boiling point, surface tension, heat of vaporization, viscosity, critical temperature, rate of evaporation, and vapor pressure do?
Boiling point increases Surface tension increases Heat of vaporization increases Viscosity increases Critical temperature increases Rate of evaporation decreases Vapor pressure decreases
Equation for volume percent
(volume of solute/volume of solution) x 100
Equation for mass percent
(mass of solute/mass of solution) x 100
Equation for mass/volume percent (%w/v)
(mass of solute in g/volume of solution in mL) x 100
Equation for mole fraction, X
(moles of solute/moles of solution)
Equation for molarity, M
Moles of solute/Liters of solution
temperature dependent
Equation for molality, m
Moles of solute/ kg of solvent
Equation for boiling point elevation
delta Tb = Kb x m x i
Equation for freezing point depression
delta Tf = Kf x m x i
Equation for osmotic pressure
pi = MRT
What is a solute?
The part of the solution that is dissolved or is the least abundant component
What is a solvent?
The dissolving agent of the solution or is the most abundant component
What three types of intermolecular forces exist in a solution?
Solute-solvent interactions, solvent-solvent interactions, and solute-solute interaction
What does “like dissolves like” imply?
Polar solutes dissolve in polar solvents; nonpolar solutes dissolve in nonpolar solvents; solutes and solvents of comparable IMF’s are soluble in each other
Define dissociation
When an ionic substance is dissolved in water and the ions that are tighty packed together in the solid become separated
Define entropy (S)
It is the measure of randomness and is directly related to the number of ways a system can disperse its energy, which is closely related to the freedom of motion of the particles; Sgas > Sliquid > Ssolid
What determines solution formation?
The relative magnitudes of delta Hsol and delta Ssoln; changes toward a state of lower enthalpy (exothermic); changes toward a state of higher entropy (more disorganized)
Describe the effect of temperature on the solubility of solids and gases.
The solubility of solids in liquids generally increases with temperature. The solubility of gases in liquids almost always decreases as temperature increases
What is Henry’s Law?
It states that the solubility of a gas, Sgas, is directly proportional to the partial pressure of the gas, Pgas, above the solution: Sgas = kH x Pgas
aka the solubility increases as the pressure increases
What causes decompression sickness (the bends)?
Scuba divers air tanks contain both nitrogen and oxygen (high concentrations of pure oxygen is toxic). As a result, high concentration of N2 is dissolved in the diver’s blood. If a diver ascends too quickly (a fast change from high pressure (where gas is soluble) to low pressure (where gas is less soluble)) the Nitrogen will separate out from the blood and form bubbles in the tissue or blood. These Nitrogen bubbles affect nerve impulses, joints, and bones and is very painful.
Define Saturated
A saturated solution is a solution that is in equilibrium with undissolved solute; additional solute will not dissolve if added to a saturated solution
Define solubility
It is the amount of solute needed to form a saturated solution in a given quantity of solvent
Define unsaturated solution
A solution that contains less solute than the amount needed to form a saturated solution
Define supersaturated solution
A solution that contains more solute that the amount needed to form a saturated solution and is unstable relative to the saturated solution
Describe the solubility of alcohols
The solubility of alcohol in polar solvents (water) decreases; the solubility of alcohol in nonpolar solvents increases (hexane, C6H14)
What is the solubility of Vitamins A, C and K3?
Vitamin A is water insoluble and fat soluble; Vitamin C is water soluble and fat insoluble; Vitamin K3 is water insoluble and fat soluble
Define miscible liquid
Pairs of liquids that mix in all proportions
Define immiscible lquid
Pairs of liquids that do not dissolve in one another
List both equations for parts per million (1 ppm)
1 ppm = (1 ug of solute)/(1 g of solution)
1 ppm = (1 mg of solute)/(1 L of solution)
What are the two types of physical properties?
Extensive (mass and volume) depend on the size of the sample; and intensive (density and temperature) do not
Define colligative property and list the properties
A colligative property of a solution is one that depends on the concentration of a solute particles and does not depend on the identity of the solute. They are: vapor pressure lowering, boiling point elevation, freezing point depression, and osmotic pressure
Equation for vapor pressure lowering (Raoult’s Law)
Psolvent = Xsolvent x P*solvent
think of it like after taxes = tax rate x before taxes
What happens when a nonvolatile solute is added to a solvent to form a solution?
The VP decreases, boiling point increases, freezing point decreases, and osmotic pressure increases
Why does the presence of nonvolatile solute particles in a liquid solvent decrease the vapor pressure above the liquid?
When a solute is added to the solvent, some of the solute molecules occupy the space near the surface of the liquid. As a result, the number of solvent molecules near the surface decreases that is, the rate at which the solvent molecules in the liquid can escape into the gas phase decreases. As a result, the vapor pressure of the solvent escaping from a solution should be smaller than the vapor pressure of the pure solvent
Define: strong electrolyte
Ions dissociate completely; soluble salts, strong acids, and strong bases
Define: weak electrolyte
Ions only partially dissociate; weak acids and weak bases
Define: nonelectrolyte
Do not dissociate into ions at all; e.g sugar
