Gen Chem Class 3 Flashcards
T/F: a physical change affects only intermolecular forces but no intramolecular forces
true
T/F: all molecules experiencce intermolecular attraction
True, at least dispersion forces
the average kinetic energy of the molecules of a substance direcly affect its _________
phase (aka state)
the phases are solid, liquid, or gas
the higher the average kinetic energy of a substance, the ____\_higher/lower___ its entropy
higher
phase transitions occur most directly as a result of change in ______
temperature,
because temperature can break and form intermolecular interactions
what are the 3 phases in order from lowest to highest kinetic energy
solid, liquid, gas
T/F when enough energy (from heat) is absorbed for molecules to move around freely around one another, the solid becomes a liquid
true
the molecules in liquid state still make contact with one another but they have enough energy to escape fixed positions
T/F: all gases are free of intermolecular forces
false, only ideal gases
T/F: molecules in the gas phase move freely from one another and experience very little if any intermolecular interactions
true
in phase change, “fusion” secribes what process?
melting
T/F: phase changes that bring molecules closer together release heat and visa versa
true
changes that bring molecules closer together are: condensation, freezing, deposition*
changes that spread molecules farther apart: melting/fusion, vaporization, sublimation**
<em>*deposition=transition from gas to solid phase</em>
<em>** sublimation=transition from solid to gas phase</em>
specific heat capacity
the amount of heat required to raise the temperature of 1 mass unit of substance by 1 degree celcius
density of ice >/< ? density of water
density of ice<density>
</density>
what does the phase diagram for water look like and why?
slope is negative because H20 is a special liquid. Its solid form actually is lower pressure than its liquid form and adding pressure will turn it into a liquid
how do you identify the mp and bp on a phase diagram
it’s the intersection of the horizonal line representing 1 atm with the lines representing barriers between phases
what equation do we use to find:
- specific heat
- temperature change for a reaction
- mass of a sample undergoing phase change
- heat added or released by substance
- c= specific heat (in cal/g·°C)
- ΔT = temperature change (in cal/g or kJ/mol)
- m=mass of sample (in g or moles)
- q=heat added or released (in cal or kcal)
q=mcΔT
the fact that water typically has a higher specific heat than other substances is because of
The breaking and reforming of hydrogen bonds in liquid water can absorb a large amount of heat, making water resistant to temperature change.
*specific heat of water is 1 cal
how do you find the amount of heat absorbed or released by a phase change?
q=nΔHfusion or vaporization
where n=amount of the substance in moles or grams depending on the terms used for ΔH.. they cancel out)
q=mount of heat absorbed or released by a phase change. in cal.
T/F: when a substance absorbs or releases heat, either its temperature changes or it will undergo a phase change but no both at the same time
true
this is represented by the heating curve
T/F: the specific heat of a substance is the same no matter what phase its in
FALSE: it depends on phase e..g. the sp. heat of liquid water is different from that of ice
1 cal is #? Joules?
1 cal = 4.2 J
ΔT is inversely proportional to ______
specific heat
from rearranging q=mcΔT
molecules with strong intermolecular forces tend to have higher/lower specific heats
higher
How do you solve this problem and why do you solve it that way?
when calculating the total energy required to go from one phase to another where the temperature changes, you have to add the product of each of the phase change equations (q=nΔH + q=mcΔT)
you solve it this way because a substance independently changes because of temperature and because of phase change but not at the same time so they have to be added.
ideal gas law
PV=nRT
P=pressure of the contained gas in atm
V=volume of container *see below
n= number of moles of substance (22.4 of ideal gas under STP)
R= universal gas constant, 0.08 L-atm/K-mol because the constant is in L, you must convert all volumes into L
T=temperature of system in Kelvin
T (in K) =?
T (in °C) + 273
How do you solve this problem?
Argon at pressure of 2 atm, fills a 0.1 L vial at a temp of 0°C. what would the pressure of the argon be if we increase the volume to 0.5L, and the temperature is 100°C.
Since it’s asking about a change and 2 terms in the equation are constant throughout the change and also not given in the problem, we can relate the before and after with a proportionality equation:
P1V1/T1 = P2V2/T2
then solve for P2
1 atm = #? torr = #? Hg ~ #? kPa
1 atm = 760 torr = 760 Hg ~ 100kPa
average kinetic energy of the molecules of an ideal gas is directly proportional to the absolute temperature of a sample
what does this look like in equation form?
KEavg ∝T
T/F: total kinetic energy of gas in a container is the same after each molecule collision as before
true
T/F: If two equal-volume containers hold gas at the same pressure and temperature, then they contain the same number of particles regardless of the identity of the gas
true
(avogadro’s law)
R (from equation for pressure)= #?
0.08
a constant
T/F: the average kinetic energies of 2 gases are not equal if the mixture is of real and ideal gases
FALSE: they are still equal as long as the gases are at the same temperature
what are the conditions that maintain ideality (i.e. make real gases act more ideal)
high temperature
low pressure
*conversely, real gases deviate most from ideal behavior under conditions of high pressure and low temperature.
mnemonic: gases can’t be their ideal selves when they are under high pressure.
the more ideal the gas the greater/weaker the intermolecular force
weaker
the molecule with the greatest number of atoms (polyatomic molecule) will take up more volume. This means that it is more/less ideal (ideal gas).
less
a molecule with one atom will take up less volume and will be most ideal, which is how the ideal gases get their name (they are gases in their atomic state)
in contrast from O2 for example which is only a gas when it’s polyatomic
T/F: H-F can take part in hydrogen bonding
true, but flourine is the only halogen that can do so
Dalton’s law
Ptot = pA + pB + pC
ie the sum of the pressure is equal to the sum of each of the pressures of the individual gases
partial pressure of a gas is equal to
its mole fraction times the total pressure
*mole fraction=fancy way of saying the ratio of particles of that gas to the total number of particles of the mixture
total pressure= in atm
effusion refers to
the escape of a gas molecule througha tiny hole comparable in size to the particle size
for two gases in the same container (kinetic energy of gases is equal), the gas with the heavier molecule will have slower/faster velocity
slower
for two gases in the same container (kinetic energy of gases is equal), how can we compare the relative velocities of each gas?
by using KE=1/2mv2 and then setting their KE equal:
1/2m1v21 = 1/2m2v22
→ v22/v21 = m1/m2
→ √ v22/v21 = √m1/m2
→ v2/v1 = √m1/m2
this gives us the ration of velocities between the gases i.g. Graham’s Law of Effusion
Graham’s Law of Effusion
(taken from setting KE1 = KE2 )
v2/v1 = √m1/m2
T/F: the molecules of 2 different gases at the same temperature in the same compartment have the same average kinetic energy
True
ideal gases take up no molecular volume
true
real gases do have volume, so if you have a mix of ideal and real gas, the total volume available to the gases is less than the total volume of the flask, whereas if it were ideal gas, the total volume available to the gas is equal to the volume of the flask.
what is the relationship between ideality, mass and intermolecular forces?
↑ideal ↓m ↓IMF
T/F: partial pressure is determined by the number of moles of a gas and is not affected by the mass of the molecules.
true, so in this picturem the partial pressure of gas x will at some point equal the partial pressure of gas y as gas Y effuses out of the container because at some point the number of particles will be the same
