chem121test3 Flashcards
energy
the ability to do work or transfer heat
thermodynamics
the study of energy and its transformations
thermochemistry
he study of chemical reactions and the energy changes that involve heat
first law of thermodynamics
Energy can be converted from one form to another, but it is neither created nor destroyed
system
The portion of the universe that we single out to study
surroundings
everything else
Open System
a region of the universe being studied that can exchange heat AND mass with its surroundings
Closed System
a region of the universe being studied that can ONLY exchange
heat with its surroundings
Isolated System
a region of the universe that can NOT exchange heat or mass with its surroundings
internal energy
the sum of all kinetic and potential energies of all components of the system; we use E to represent it
change in internal energy
ΔE = Efinal − Einitial
if ΔE negative
loss of energy
if ΔE positive
gain of energy
heat
q
work
w
change in internal energy type 2
ΔE = q + w
exothermic
releases energy to the environment
endothermic
absorbs energy from the environment
state functions
an absolute variable that doesn’t require comparison
w =
PΔV
enthalpy
the internal energy plus the product of pressure and volume
enthalpy equation
H = E + PV
enthalpy of reaction
The change in enthalpy, ΔH, is the enthalpy of the products minus the enthalpy of the reactants
enthalpy is
an extensive propertythe
calorimetry
the measurement of heat flow
calorimeter
the instrument used to measure heat flow
heat capacity
the amount of energy required to raise the temperature of a substance by 1K(1 C)
specific heat
the amount of 1 gram of a substance heated by 1K
molar heat capacity
the amount of 1 mole of a substance heated by 1K
specific heat of water
4.184 J/g-K
calorimeter equation
qsoln = Cs × msoln × ΔT = –qrxn
bomb calorimeter equation
qrxn = – Ccal × ΔT
Hess’s law
a state function that says that if it takes multiples steps to get to a point then the enthalpy will be an addition of both
enthalpy of formation
the enthalpy change for the reaction in which 1 mole of a compound is made from its constituent elements in their elemental forms
standard of formation
25 C and 1 atm
Hess’s Law Equation
ΔH = ΣnΔHf°,products – ΣmΔHf°,reactants
Bond enthalpy
The enthalpy associated with breaking one mole of a particular bond in a gaseous substance.
Characteristics of gases
Physical properties of gases are all similar.
Composed mainly of nonmetallic elements with simple formulas and low molar masses.
Unlike liquids and solids, gases
expand to fill their containers.
are highly compressible.
have extremely low densities.
Two or more gases form a homogeneous mixture.
Pressure
the amount of force applied to an area
Units of preasure
Pascals, bars, mm Hg, atm
pressure conversions
1 atm = 760. torr = 760. mm Hg = 101.325 kPa = 1.10325 bar
Barometer
measures the atm pressure by measuring how far the mercury goes up a defined tube
manometer
used to measure the difference in pressure between atmospheric pressure and that of a gas in a vessel
STP
1 atm, 760 torr (760 mm Hg), 101.325, 0 C or 273.15 K
Boyle’s law
The volume of a fixed quantity of gas at constant temperature is inversely proportional to the pressure
Boyle’s law equation
P1V1 = P2V2
Charles’ law
The volume of a fixed amount of gas at constant pressure is directly proportional to its absolute temperature.
Charles’ law equation
V1/T1 = V2/T2
Combined gas law
P1V1/T1=P2V2/T2
Gay-Lussac’s Law of
Combining Volumes`
At a given temperature and pressure, the volume of gases that react with each other is in small whole numbers
avogadro’s law
The volume of a gas at constant temperature and pressure is directly proportional to the number of moles of the gas
at stp one mole of any gas occupies
22.4 L
avogadro’s law equation
V1/n1 = V2/n2
l-atm/mol-K
0.08206
J/mol-K
8.314
density of gas equation
d = MM*P/RT
molar mass of gas quation
MM = mRT/PV
Dalton’s Law of Partial Pressures
If two gases that don’t react are combined in a container, they act as if they are alone in the container.
The total pressure of a mixture of gases equals the sum of the pressures that each would exert if it were present alone.
mole fraction
ratio of moles of a substance to total moles
Main Tenets of Kinetic-Molecular Theory
Gases consist of large numbers of molecules that are in continuous, random motion.
The combined volume of all the molecules of the gas is negligible relative to the total volume in which the gas is contained.
Attractive and repulsive forces between gas molecules are negligible
Energy can be transferred between molecules during collisions, but the average kinetic energy of the molecules does not change with time, as long as the temperature of the gas remains constant.
The average kinetic energy of the molecules is proportional to the absolute temperature
the lighter gas
moves faster at a constant temperature
effusion
the escape of gas molecules through a tiny hole into an evacuated space
diffusion
the spread of one substance throughout a space or a second substance
Graham’s Law
The “lighter” gas always has a faster rate of speed
Deviations from Ideal Behavior
The assumptions made in the kinetic-molecular model (negligible volume of gas molecules themselves, no attractive forces between gas molecules, etc.) break down at high pressure and/or low temperature
The van der Waals Equation
corrects the behavior that real gases exert
