Ch 11 Chemistry
Terms in this set (59)
Order the Rate of Diffusion from slowest to fastest
Solid, liquid, gas
Is virtually incompressible
liquid and solid
solids and liquids, particles are fairly close together compared with that of a gas.
Is the density of a substance in liquid state closer to density in gaseous state or solid state?
Density of a liquid is much closer to a solid than a gas
What does the state of a substance depend on?
balance between the kinetic energies of the particles and the interparticle energies of attraction
What happens when the temperature of a gas decreases?
the avg. kinetic energy of its particles decrease, allowing the attractions between the particles to first draw the particles closer together, forming a liquid, then lock them into place, forming a solid.
When Pressure of a gas increases?
brings molecules closer together, making IMFs more effective, can drive phase changes
Strengths of intra/inter molecular forces
Intra are usually stronger (covalent, ionic, metallic bonds). Less energy is require to break intermolecular forces and vaporize a liquid or melt a solid. When phase change happens, molecules usually stay intact
reflect strength of intermolecular forces, molecules must overcome their attractive forces in order to separate and form a vapor.
Why are intermolecular so much weaker than intramolecular?
charges responsible for intermolecular are smaller, dipole moment of HCl, +.718 and -.718 from hydrogen to chlorine ends of molecule. Also greater distance. Lesser charge and greater distance = weaker forces
How do electrically neutral, nonpolar atoms and/or molecules form attractions between each other?
Dispersion forces. Motion of electrons in an atom or molecule can create an instantaneous or momentary dipole.
How are helium atoms attracted to one another?
the average distribution of electrons is spherically symmetrical, no permanent dipole moment. Instantaneous distribution of the electrons can be different from the avg. distribution, the motions of an electron in one atom influence the neighboring atom.
the ease with which the charge distribution is distorted in a molecule. "squashiness" of electron cloud.
More polarizable molecules have:
larger dispersion forces.
When do dispersion forces increase?
increase in strength with increasing molecular weight, hence number of electrons and atomic/molecular size.
Order strength of LDF forces: F2, I2, Cl2, Br2
F2, Cl2, Br2, I2
the presence of a permanent dipole moment in polar molecules. Originate from electrostatic attractions between partially positive end of one molecule and partially negative end of a neighboring molecule. Repulsions can also occur.
When are dipole-dipole forces effective?
when molecules are very close together. Repulsive and attractive interactions, more attractive than repulsive, attractive spend more time near each other.
For molecules of approx. equal mass and size, strength of intermolecular forces increases with:
increasing polarity. Dipole-dipole
the strong intermolecular attractions in HF, H2O, NH3 result from this. Special type of intermolec. attraction between the H atom in a polar bond ( particularly H-F, H-O, H-N) and non bonding electron pair on a nearby small electronegative atom or ion usually F, O, N (in another molecule).
Type of dipole-dipole interaction
hydrogen bonds. Because of the electronegativity of H, F, and N.
Why is hydrogen different?
It has no inner electrons. Positive side of the dipole has the concentrated charge of the nearly bare hydrogen nucleus. Positive charge is attracted to the negative charge of an electronegative atom in a nearby molecule. Electron poor hydrogen is so small, can approach an electroneg. atom and interact strongly with it.
What forces are generally stronger than london dispersion or dipole-dipole forces?
What forces are generally stronger than london dispersion or dipole-dipole forces?
When does the magnitude of attraction increase for a ion-dipole force?
as ionic charge or dipole moment increases.
If ions are present, polar molecules are present, and no H atoms bonded to F, N, O atoms
Dipole - dipole forces and dispersion forces
If polar molecules arent present?
dispersion forces only, CH4, Br2.
When molecules have comparable molecular weights and shapes?
dispersion forces are approx. equal in the 2 substances. Difference in the magnitude of intermolecular forces is due to strengths of dipole-dipole attractions.
When molecules have very different molecular weights...
dispersion forces tend to determine which substance has stronger intermolecular attractions.
resistance of a liquid to flow, the greater the viscosity, the more slowly it flows. Decreases with increasing temperature and increases with increasing molecular weight.
Related to the ease with which molecules of a liquid can move relative to one another
A measure of the net inward force that must be overcome to expand the surface area of a liquid
given by surface tension
the energy required to increase the surface area of a liquid by a unit amount
intermolecular forces that bind a substance to a surface
adhesive forces , H20, concave, smiley meniscus
intermolec. forces that bind similar molecules to each other
cohesive ( Mg) convex, frowny meniscus
small-diameter glass tube in liquid, the rise of liquid up very narrow tubes.
How does capillary action work?
adhesive forces between the liquid and the walls of the tube increase the surface area of the liquid, the surface tension tends to reduce the area, pulling liquid up the tube.
exist between an ion and a polar molecule. Cations are attracted to the negative end of a dipole, anions attracted to the positive end.
phase change of gas to a solid
phase change of a gas to a liquid
heat of fusion
a measure of the increased freedom of motion of the particles, solid to a liquid.
as the temperature of a liquid increases, the particles move with increasing energy. A way to measure this energy, the concentration of gas-phase particles above the liquid surface, exert a pressure.
Vapor pressure ________ with increasing temperature until it ____ the external pressure above the liquid, typically atmospheric pressure.
Heat of fusion + heat of vaporization
heat of sublimation (solid to a gas) endothermic
Heat of condensation is ______ in magnitude to heat of vaporization and has _______ sign.
In a heating curve, the temperature of the system increases only when:
all ice becomes liquid, or all liquid becomes gas
Why is temperature constant between the phase changes in the heating curve of water?
the added energy is used to overcome the attractive forces between molecules rather than to increase their average kinetic energy.
the highest temperature at which a distinct liquid can form
the pressure required to bring about liquefaction at critical temp.
temp exceeds critical temp and pressure exceeds critical pressure
when evaporation and condensation occur at equal rates
when a liquid and its vapor are in dynamic equilibrium.
substances with high vapor pressure, evaporate readily, gasoline.
as temperature increases, the rate of molecules escaping into the gas phase :
increase, the molecules have more kinetic energy, the vapor pressure increases.
Which is more volatile, CCl4 or CBr4?
CCl4, both are non polar, only dispersion forces. Dispersion forces are stronger for heavier CBr4, has a lower vapor pressure than CCl4. The substance w a larger vapor pressure is more volatile.
The_____the intermolecular forces in a liquid, the more _____ the molecules can escape and the _____ the vapor pressure at a given temperature,
weaker, easily, higher
A liquid boils when:
its vapor pressure equals the external pressure acting on the liquid surface. Bubbles of vapor form within the liquid.
The temp. at which a liquid boils _____ with increasing external pressure
graphic way to summarize the conditions under which equilibria exist btw the different states of matter. 3 important curves, represents the pressure and temperature at which the various phases can coexist.
If the pressure exerted on a liquid is increased, while temp is held constant, what type of phase transition will eventaully occur?
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