thermodynamics Flashcards
what is Boyles law?
The volume of gas is inversely proportional to the pressure at constant temperature.
what is Charles law ?
the volume of an ideal gas at constant pressure is directly proportional to the temperature.
what is avogadros principle?
equal volumes of gases under the same conditions contain the same number of molecules.
what is the ideal gas equation?
pV = nRT
what is the gas constant ? including units
8.3145 J Mol-1 K-1
what is 1 bar in pascals?
1 x 10^5 Pa
what is the partial pressures equation?
pi = xi . ptotal
what is the definition for heat?
The transfer of energy as a result of the temperature difference between the system and its surroundings.
what is the definition for work ?
This is the mode of transfer of energy that achieves or utilizes uniform motion of atoms in the surroundings.
what is a diathermic wall?
it permits the passage of energy as heat
what is an adiabatic wall?
its doesn’t permit the passage of heat as energy, even if there is a temperature diofference across the wall.
what is irreversible work ?
when a gas expands against a constant external pressure.
what is the equation for irreversible work?
- on equation sheet
work = -pex . deltaT
a system in ______ does maximum expansion work
mechanical equilibrium
what is reversible work?
when pex = pgas
what is the equation for reversible work?
- on equation sheet
work = -nRT . ln(v2/v1)
what is the internal energy (U)?
the sum of all the kinetic and potential contributions to the energy of all the atoms, ions, and molecules in the system.
total energy of a system
when there is a change in volume how do you calculate the change in internal energy
- on equation sheet
deltaU = q + w
for an isolated system q and w =
0 , therefore the internal energy of an isolated system is constant
when there is constant volume how do you measure the change in internal energy
deltaU = q
what is the equation for a change in enthalpy, in terms of internal energy.
- on equation sheet
deltaH = deltaU + p . deltaV
what is the enthalpy of vaporisation ?
the energy that must be supplied as heat at constant pressure to convert 1 mole of liquid into the gaseous phase
what is the equation for the enthalpy of vaporisation, for a non constant pressure?
deltavapH = qp/n
deltaH = ? at constant pressure
q (heat)
what is the enthalpy of fusion?
the energy that must be supplied as heat at constant pressure to convert 1 moles of a solid to the liquid phase.
what is sublimation
the direct conversion of a solid to a vapour
enthalpy of sublimation =
enthalpy of fusion + enthalpy of vaporisation
what is combustion
when a substance reacts with oxygen
what is Hess’s Law
the total enthalpy change during the complete course of a chemical reaction is independent of the sequence of steps taken.
what’s the equation for entropy change ?
deltaS = q(rev) / T
what the equation of entropy change accompanying reversible expansion?
- on equation sheet
deltaS = nR ln(v1/v2)
what is the equation for entropy change accompanying a phase transition, when you have the enthalpy change.
deltaS = deltaHtr / Ttr
tr = the transition of interest
- we use delta H as when at constant pressure qrev = deltaH
what does Troutons rule show us
that the change in entropy accompanying vaporisation is the same for all liquids at their boiling temperatures.
this is around +85 J K-1 mol-1
if a compound has _____ bonding then it becomes an exception to Troutons rule
hydrogen
what is the equation for entropy when there is a change in temperature.
- on equation sheet
deltaS = C ln (T2/T1)
where C is the heat capacity of the substance of interest
for entropy of mixing we note that each gas has performed an ______ expansion.
isothermal, reversible
what is the equation for the entropy of mixing
- on eqaution sheet
= -R , sum(xi . ln(xi))
what is the equation for Gibbs energy change
deltaG = deltaH - TdeltaS
what is the difference between deltaGstandard and deltaG ?
The change in Gibbs free energy is under the conditions of the reactants. Whereas the change in Gibbs free energy of pure, unmixed products and reactants under standard conditions, is at the specified temperature and the pressure of one bar.
what’s the equation for finding the change in Gibbs energy at a given point during a reaction? (when mixing is occurring)
- on equation sheet
deltarG = deltarGstandard + RT ln(Q)
where Q is the reaction quotient
a system comes to equilibrium when it reaches ____
its minimum Gibbs energy
at equilibrium deltaG =
0
therefore 0 = deltarGstandard + RT ln(K)
(swapping Q for K as its at equilibrium.)
how do you convert cm^3 to m^3
x10^-6
what unit should the v be in when dealing with the ideal gas equation
m^3
how do you calculate the enthalpy of vaporisation at a constant pressure
q/n
- remove p from the equation
- only include p when your measure a specific pressure when the pressure changes.
combine work and the ideal gas equation
w = -nRT
what unit is entropy measured in
J K-1
what K should you add to celsius to covert it
273.15
how to convert 1 atm to pa
1 atm = 101325 pa
for a isothermal process (constant temperature) the change in internal energy is …
0, this means that 0 = q + w
