enthalpy Flashcards
core definitions, heat capacity, enthalpy and gas expansion
work definition
transfer of energy to ordered motion
heat definition
chaotic transfer of energy
internal energy definition
the sum of all kinetic and potential energy of a species
relationship between Cp and Cv
Cp = Cv + R
Equipartition theory values
translation = 1.5R
rotation = 1.5/1 R
vibration = R mol-1
What is the sum of the equipartition values
heat capacity per mole
enthalpy change with volume definition
dH = dU + pdV OR
dH = dU + dnRT
when is enthalpy change and its relation to pressure relevant
For gases, for liquids and solids there is little change in volume with changes in enthalpy
what is enthalpy change at constant pressure
q (heat)
isothermal conditions
systems can exchange heat with their surroundings (constant temperature)
isothermal work equation
w = p*dV
instantaneous isothermal expansion
instantaneous inherently means that pressure is constant
w = -pdV
work done by infinitely slow (reversible)
isothermal expansion
w = - RTln(Vf/Vi)
dU for a perfect gas
dU = q + w (balance between work done and heat exchanged)
adiabatic conditions
cannot exchange heat with their surroundings
what is lamda
Cp/Cv
what is pressure proportional to under adiabatic conditions
1/V^lamda
c definition
Cv,m/R (molar Cv/R)
Temperature change under adiabatic conditions
Tf = Ti(Vi/Vf)^1/c
Finding enthalpy given Cp and T under adiabatic conditions
The area under a plot of Cp against T
Final enthalpy under adiabatic conditions
H2 = H1 + integral(Cp(T))
The Kirchhoff equation
(dH/dT) = dCp
Calculating Cv from a calorimeter
E = IVt
IV = W and I is the current and V is the voltage
t is time in s
then E = qv = CvdT
Converting internal energy to enthalpy of a gas
dH = dU + dnRT
where dn is the change in the number of moles of a gas during chemical reaction
Internal energy from a calorimeter
dU = CvdT
pressure and volume after irreversible isothermal or adiabatic expansion
isothermal : p1V1 = p2V2
adiabatic: p1V1^lamda = p2V2^lamda
