CHEM 135 EXAM 3
• Calculate the Hrxn from constant pressure (i.e., "coffee-cup") calorimeterdata: 1)qsoln=
msoln x ”Tsoln x Csoln
2) qsoln=-qrxn
3) ”Hrxn=qrxn/(moles of the sample in the reaction)
Use molar mass and given mass to solve for the number of moles in the denominator4)final unit
should be in J
• If a chemical equation is multiplied by some factor: ”Hrxn is also multipliedby the same
factor.
• If a chemical equation is reversed: ”Hrxn changes sign.
• If a chemical equation can be expressed as the sum of a series of steps: ”-Hrxn for the
overall equation is the sum of the heats of reactions for each step.
• For a Pure Compound: The standard enthalpy of formation is the change in enthalpy
when 1 mole of the compound forms from its constituent elements in theirstandard states.
• For a Pure Element in Its Standard State: ”Hf°=0
• ”Hf° units: kJ/mol
• dispersion force: -The one intermolecular force present in all molecules andatoms
-A larger electron cloud results in a greater dispersion force because the electronsare held less
tightly by the nucleus and can therefore polarize more easily.
• Dipole-dipole: A molecule has dipole-dipole forces if it is polar.
• Hydrogen bonding: -Polar molecules containing hydrogen atoms bonded di- rectly to
small electronegative atoms—most importantly fluorine, oxygen, or nitrogen
-The result is a strong attraction between the hydrogen in each of these moleculesand the F, O,
or N on its neighboring molecule, an attraction called a hydrogen bond
• Ion-dipole: -occurs when an ionic compound is mixed with a polar compound
-ion-dipole forces are the strongest of the types of intermolecular forces
-responsible for the ability of ionic substances to form solutions with water
• Intermolecular force strength:
• As the boiling/melting point increases: the strength of the intermolecularforces increase
• As the molecular polarity increases: the strength of the intermolecular forcesincrease
• Enthalpy increases as the: strength of intermolecular forces increase
, • Vapor Pressure increases as the: strength of intermolecular forces decreases
• Vapor pressure: The partial pressure of a vapor in dynamic equilibrium with itsliquid.
• Heat of vaporization: The amount of heat required to vaporize one mole of aliquid to a
gas.
• Normal boiling point: The temperature at which the vapor pressure of a liquidequals 1
atm.
• Actual boiling point: The temperature at which the vapor pressure of a liquidequals the
external pressure.
• Fusion: -Phase transition from solid to liquidH2O (s)+Heat’ H2O (l)
”Hrxna”Hfusion
• Deposition: -The phase transition from gas to solid.
H2O (g)’ H2O (s) + Heat
”Hrxna”Hdeposition ”Hrxna”H
- sublimation
• Vaporization: -The phase transition from liquid to gas.H2O (l)+Heat’ H2O (g)
”Hrxna”Hvaporization
• Condensation: The phase transition from gas to liquid.
H2O (g)’ H2O (l)+Heat
”Hrxna”Hcondensation ”Hrxna”H
- vaporization
• Sublimation: -The phase transition from solid to gas.H2O (s)+ Heat’ H2O (g)
”Hrxna”Hsublimation
• Crystallization: -The phase transition from liquid to solidH2O (l)’ H2O (s)+Heat
”Hrxna”HCrystalization ”Hrxna”H
- fusion
• When the graph plateaus that represents a (blank) at the given tempera-ture: phase change
• vapor pressure increases with: increasing temperatures
• Clausius-Clapeyron equation for a line: ln Pvap=(”Hvap/R)(1/T)+ln ²
-Pvap: vapor pressure(torr)
-’:constant that depends on gas
-”Hvap:heat of vaporization(J/mol)
-R: gas constant 8.314
• Clausius-Clapeyron equation two point:
• Calculate the Hrxn from constant pressure (i.e., "coffee-cup") calorimeterdata: 1)qsoln=
msoln x ”Tsoln x Csoln
2) qsoln=-qrxn
3) ”Hrxn=qrxn/(moles of the sample in the reaction)
Use molar mass and given mass to solve for the number of moles in the denominator4)final unit
should be in J
• If a chemical equation is multiplied by some factor: ”Hrxn is also multipliedby the same
factor.
• If a chemical equation is reversed: ”Hrxn changes sign.
• If a chemical equation can be expressed as the sum of a series of steps: ”-Hrxn for the
overall equation is the sum of the heats of reactions for each step.
• For a Pure Compound: The standard enthalpy of formation is the change in enthalpy
when 1 mole of the compound forms from its constituent elements in theirstandard states.
• For a Pure Element in Its Standard State: ”Hf°=0
• ”Hf° units: kJ/mol
• dispersion force: -The one intermolecular force present in all molecules andatoms
-A larger electron cloud results in a greater dispersion force because the electronsare held less
tightly by the nucleus and can therefore polarize more easily.
• Dipole-dipole: A molecule has dipole-dipole forces if it is polar.
• Hydrogen bonding: -Polar molecules containing hydrogen atoms bonded di- rectly to
small electronegative atoms—most importantly fluorine, oxygen, or nitrogen
-The result is a strong attraction between the hydrogen in each of these moleculesand the F, O,
or N on its neighboring molecule, an attraction called a hydrogen bond
• Ion-dipole: -occurs when an ionic compound is mixed with a polar compound
-ion-dipole forces are the strongest of the types of intermolecular forces
-responsible for the ability of ionic substances to form solutions with water
• Intermolecular force strength:
• As the boiling/melting point increases: the strength of the intermolecularforces increase
• As the molecular polarity increases: the strength of the intermolecular forcesincrease
• Enthalpy increases as the: strength of intermolecular forces increase
, • Vapor Pressure increases as the: strength of intermolecular forces decreases
• Vapor pressure: The partial pressure of a vapor in dynamic equilibrium with itsliquid.
• Heat of vaporization: The amount of heat required to vaporize one mole of aliquid to a
gas.
• Normal boiling point: The temperature at which the vapor pressure of a liquidequals 1
atm.
• Actual boiling point: The temperature at which the vapor pressure of a liquidequals the
external pressure.
• Fusion: -Phase transition from solid to liquidH2O (s)+Heat’ H2O (l)
”Hrxna”Hfusion
• Deposition: -The phase transition from gas to solid.
H2O (g)’ H2O (s) + Heat
”Hrxna”Hdeposition ”Hrxna”H
- sublimation
• Vaporization: -The phase transition from liquid to gas.H2O (l)+Heat’ H2O (g)
”Hrxna”Hvaporization
• Condensation: The phase transition from gas to liquid.
H2O (g)’ H2O (l)+Heat
”Hrxna”Hcondensation ”Hrxna”H
- vaporization
• Sublimation: -The phase transition from solid to gas.H2O (s)+ Heat’ H2O (g)
”Hrxna”Hsublimation
• Crystallization: -The phase transition from liquid to solidH2O (l)’ H2O (s)+Heat
”Hrxna”HCrystalization ”Hrxna”H
- fusion
• When the graph plateaus that represents a (blank) at the given tempera-ture: phase change
• vapor pressure increases with: increasing temperatures
• Clausius-Clapeyron equation for a line: ln Pvap=(”Hvap/R)(1/T)+ln ²
-Pvap: vapor pressure(torr)
-’:constant that depends on gas
-”Hvap:heat of vaporization(J/mol)
-R: gas constant 8.314
• Clausius-Clapeyron equation two point:
