chem test 3 Flashcards
boyle’s law
volume of a gas is inversely proportional to its pressure at a constant temperature, PV=const T
charles law
volume of a gas is directly proportional to its temperature at constant pressure, V/T=const P
combined gas law
PV/T=const at const # moles, P1V1/T1=P2V2/T2
avogadro’s hypothesis
equal volume of gases at the same temperature and pressure will have an equal number of moles and molecules
ideal gas law
PV=nRT
R
.08206 Latm/Kmol
8.314 J/Kmol
daltons law
partial pressures, total pressure for a mixture of gases is the sum of the partial pressure of each gas, P=ΣPi
mole fraction
moles of i/total moles=mole fraction xi
no unites
sum =1
kinetic molecular theory of gases
gases made up of very small molecules
molecules are in continuous random motion
average kinetic energy is 1/2Mv^2=32RT
collisions with the walls and other molecules are perfectly elastic
root mean square velocity (average velocity)
U(rms)=[3RT/M]^(1/2)
grahams law
of effusion (no room for molecule to come in while another one leaves) rate of effusion of a gas is inversely proportional to the square root of the molecular weight of the gas
two reasons that real gases not ideal
real gases have attractions between the molecules, so collisions are not perfectly elastic
real gas molecules are small, but not infinitely small, they have volume
(P+n^2+a/v^2)(V-nb)=nRT
van der Waals equation
a is a measure of the attractive forces between the gas molecules
b is a measure of the size of the gas molecules
kinetic energy
energy due to motion
potential energy
energy due to position
thermal energy
energy due to temperature
first law of thermodynamics
energy can neither be created nor destroyed, ΔE=q+w
two kinds of heat
latent and change in temp
change in temp equation
q=mCΔT
exothermic
heat given off, ΔH
endothermic
heat is absorbed, ΔH>0
equation for work
w= -PΔV
enthalpy
heat involved in constant pressure process
ΔH
symbol for change in enthalpy
calorimeter
device used to measure heat
says enthalpies of reaction are additive
Hess’
ΔH^o f
symbol for standard enthalpy of formation
significance of ΔH
heat involved in a constant pressure process, and chemists do a lot of things at constant pressure
Hess’ law
law of constant heat summation, add up delta H’s
ΔH^o
standard=1 atm pressure and 25oC
standard enthalpy of formation
ΔH^o f, delta h for the formation of 1 mole of the substance from its elements in their standard state at 1 atm and 25oC, products-reactants
bond energy
average energy required to break a particular bond in the gas phase
bomb calorimeter
piece of equipment that is used to fine experimental values of standard enthalpies of combustion, by burning sample in high oxygen concentration all delta Hoc values are negative
coffee cup calorimeter
coffee cup calorimeter is a device used to measure delta Ho for reactions in solution
spontaneous change
change that takes place without the need to provide heat
thermodynamics
scientific study of heat, work, and energy
second law of thermodynamics
entropy of the universe for aspontaneous change always increases
ΩS(universe)>0
entropy
S is a measure of the randomness of the system
S=klnΩ (omega ways to arrange the system)
k=boltzmann’s constant=R/Na=1.38x10^-23 J/K
ΔS=ΔH/T
formula for ΔS
ΔSo
change in the entropy (products-reactants) for a reaction at a standard state
So
absolute entropy of a substance
NEVER A CHANGE
third law of thermodynamics
entropy of any perfectly cystalline substance at absolute 0K is zero
So0=0
So(0)=0
absolute entropies determined
So298=So0 + integral 0 to 298 C/T dt
another name for absolute entropies
third law entropies
reaction is more likely to occur if the energy (enthalpy) does what
enthalpy goes down (decreases,
reaction is more likely to occur if the entropy does what
goes up (increases, >0, endothermic)
Gibbs Free energy
combination of enthalpy and entropy, J or kJ/mol
ΔG=ΔH-TΔS
if delta G is negative, the reaction is spontaneous
driving force for spontaneity
what makes delta G
ΔGof
standard Gibbs free energy of formation
delta Go for the reaction forming 1 mole of the substance from its elements in their standard states
