Chapter 11: Liquids and Intermolecular Forces Flashcards
What does the state of a substance depend on?
the balance between the KE of particles and the attraction energies between particles
Which one is weaker: intermolecular forces or intramolecular forces?
intermolecular forces
What are the 4 types of intermolecular forces?
dispersion forces | dipole-dipole interactions | ion-dipole | hydrogen bonding
What are van der Waals forces?
dispersion forces and dipole-dipole interactions
Who discovered dispersion forces?
Fritz London
What are (London) dispersion forces?
one atom’s movement of electrons influence that of its neighbor atoms SO = an INSTANTANEOUS dipole on one atom can induce an instantaneous dipole on an adjacent atom
What does the strength of the dispersion force depend on?
the polarizability of a molecule
What is the polarizability of a molecule?
how charge distribution is manipulated to induce the instantaneous dipole
What does an increase in the polarizability of a molecule indicate?
easier the electron cloud could be manipulated to give an instantaneous dipole
What is the relationship between dispersion forces and molecular weight and its affect on boiling point?
dispersion forces are stronger as MW increases = increases boiling point
What are dipole-dipole interactions due to?
permanent dipole moments in polar molecules
When are dipole-dipole and dispersion interactions effective?
when the molecules are very close to each other
What is hydrogen bonding?
an attraction between the H (of an -OH, -NH, or -FH) and a nearby electronegative atom in another molecule/compound
What are ion-dipole forces?
exists between an ion and a polar molecule (ie: NaCl in H2O)
In what substances are dispersion forces found?
ALL substances
Order the 4 intermolecular forces from strongest to weakest.
ion-dipole > H-bonding > dipole-dipole > dispersion
What is viscosity?
resistance of a liquid to flow | how easily do molecules flow past each other
What does an increase in viscosity indicate?
slow flow
What does a decrease in viscosity indicate?
fast flow (like water)
What does viscosity depend on?
attractive forces between the molecules
What is the SI unit for viscosity?
kg/ms
How does a increase in temperature affect viscosity?
decrease in viscosity
What is surface tension?
molecules at the surface experience a net inward force that pulls them closer to the middle = decrease in surface area
What is surface tension due to?
the imbalance of intermolecular forces at the surface of the liquid
What is the unit for surface tension?
J/m^2
What is capillary action?
crawl of liquids up a very narrow tube
What is cohesive forces?
intermolecular forces that bind similar molecules to one another
What is adhesive forces?
intermolecular forces that bind a substance to a surface
What causes the convex meniscus of water? (cohesion adhesion relationship)
cohesion forces H2O < adhesion forces H2O
What causes the concave meniscus of Hg? (cohesion adhesion relationship)
cohesion forces Hg > adhesion forces Hg
What are phase changes?
state changes of a substance | transformations
What is sublimation?
solid changes directly to gas
What is fusion?
melting
What is heat of fusion?
(∆Hfus) energy that allows increased freedom of motion particles
What is vapor pressure?
pressure exerted by the vapor of a liquid when the liquid and vapor are in dynamic equilibrium
How does an increase in temperature affect vapor pressure of a gas in solution?
increases vapor pressure until vapor pressure equals the external pressure above the liquid
What is heat of vaporization?
(∆Hvap) energy needed for a quantity of liquid to change into vapor (gas)
What is heat of sublimation?
(∆Hsub) energy needed for solid to directly change into gas
What is the relationship between the heat of sublimation, heat of vaporization and heat of fusion?
∆Hsub = ∆Hvap + ∆Hfus
What is the opposite of sublimation?
deposition
What is the opposite of vaporization?
condensation
What is the opposite of fusion?
freezing
What is critical temperature?
highest temperature at which a distinct liquid phase can form and liquid can exist at
What is critical pressure?
pressure needed to bring about the liquefaction at the critical temperature
How does an increase in intermolecular forces strength affect critical temp/pressure?
increases critical temp/pressure
What is supercritical fluid?
when temperature > critical temp and pressure > critical pressure BUT liquid and gas phases are indistinguishable from each other
What state is supercritical fluid in?
gas/liquid = can expand to fill container but molecules are still close to each other
What is dynamic equilibrium?
condition where 2 opposing processes occur at the same time at equal rates
What is volatile?
describes liquids that readily evaporate
How does intermolecular forces and vapor pressure affect how volatile a liquid can be?
liquid with weak intermolecular forces and high vapor pressure = highly volatile (compare with strong IMForces and low vapor pressure)
What is a boiling point?
temperature at which its vapor pressure equals the external pressure acting on the liquid’s surface
What is a normal boiling point?
boiling point of a liquid at 1 atm
What are the 3 curves on a phase diagram (temp vs pressure)?
vapor pressure curve | sublimation curve | melting curve
What does the vapor pressure curve represent?
equilibrium between liquid and gas phases
What is the critical point?
critical temperature and critical pressure
What does the sublimation curve represent?
change in vapor pressure of the solid as it sublimes at different temperature | curve is the equilibrium between solid and gas phases
What does the melting curve represent?
change in melting point of a solid as pressure changes | curve is the equilibrium between solid and liquid phases
What is the normal melting point?
melting point at 1 atm
What is the triple point?
where all 3 phases are in equilibrium as their curves all intersect at this point
