Thermochemistry Flashcards
isolated system
cannot exchange energy (heat and work) or matter with the surroundings
closed
system can exchange energy (heat and work) but not matter with the surroundings
open
system can exchange both energy (heat and work) and matter with the surroundings
first law of thermodynamics
deltaU = Q - W
U: internal energy of the system
Q: heat added to the system
W: work done by system
isothermal process
- systems temp is constant
- when deltaU is 0, like this case, the
Q = W
adiabatic process
- occurs when no heat is exchanged between the system and the environment, thus thermal energy of the system is constant throughout the process
- common bc temp and pressure control are easy
- Q = 0
- deltaU = -W
isobaric process
- pressure of the system is constant
- common bc temp and pressure control are easy
isovolumetric (isochoric) process
- experience no change in volume
- W = 0
- deltaU = Q
critical point
boundary between liquid and gas phases
no distinction between the two
supercritical fluid
results from the passage of the critical point
endothermic
deltaQ > 0
exothermic
deltaQ < 0
conversion between cal and joule
1 cal = 4.184 J
enthalpy deltaH
- equivalent to Q heat under constant pressure
calculating heat absorbed or lost
q = mc • deltaT
specific heat
- the amount of energy requires to raise the temp of one gram of a substance by one degree
- water specific heat is 1 (cal/g•K)
heat capacities
mass • specific heat
constant-pressure calorimeter
an insulated container covered w a lid and filled with a solution in which a rxn or some physical process is occurring
bomb calorimeter (decomposition vessel)
- type of constant-volume calorimeter
- material is placed in steel decomp vessel which is then almost filled with pure oxygen gas
- then placed in an insulated container holding a known mass of water
- contents electrically ignited
- material combusts
- delta V = 0 and thus W = 0
bomb calorimeter thermodynamics
deltaUsys = -deltaUsurr
qsys = -qsurr
enthalpy (H)
change in enthalpy is equal to heat transferred into or out of rxn
deltaH = Hproducts - H reactants
positive, endothermic
neg, exothermic
standard enthalpy of formation
enthalpy required to produce one mole of a compound from its elements in their standard states
298K and 1 atm
Hess’s Law
deltaH = deltaH1 + deltaH2 + deltaH3
deltaH°rxn
deltaH°rxn = ξdeltaHbonds broken - ξdeltaHbonds formed
considering bond enthalpy
deltaS
deltaS = Qrev/T
measure of spontaneous dispersal of energy at specific temp and how much energy is spread out
deltaSuni = deltaSsys + deltaSsurr > 0
standard entropy change for a rxn
deltaS°rxn = ξdeltaS°fproducts - ξdeltaS°freactants
