Ch. 7: Thermochemistry Flashcards
Can an Isolated System exchange energy or matter with the surroundings
no exchange of energy (heat or work) with surroundings
ex: insulated bomb calorimeter
Can a Closed System exchange energy or matter with the surroundings
exchange of energy (heat or work) but not matter with surroundings
ex: steam radiator
Can an Open System exchange energy or matter with the surroundings
exchange of energy (heat or work) and matter with surroundings
ex: pot of boiling water
what is a process
changing in one of the properties of a system
equation for delta U
delta U = Q - W
change in internal energy of a system = heat added - work done by system
FIRST LAW OF THERMO
what occurs in an isothermal process
- temperature is constant
- U (total internal energy) is constant, delta U = 0
- Q = W
what occurs in an adiabatic process
- no heat is exchanged between system and environment (temperature can change)
- Q = 0
- delta U = - W (change in internal energy = work done on the system)
what occurs in an isobaric process
- pressure is constant
- delta U = Q - W
what occurs in an isovolumetric (isochoric) process
- volume is constant
- no change in volume = W = 0
- delta U = Q
how is a spontaneous process driven
occurs internally WITHOUT drive by outside energy source
what is accomplished by coupling
energy for nonspontaneous rxns is supplied by linking them with spontaneous rxns
state functions
properties of a system at equilibrium
- pressure (P)
- density (p)
- temperature (T)
- volume (V)
- enthalpy (H)
- internal energy (U)
- Gibbs free energy (G)
- entropy (S)
process functions
properties of a system in flux
- work (W)
- heat (Q)
standard condition
- 25 degrees C (298K)
- 1 atm
- 1 M con’c
used for kinetics, e’q, and thermo, measuring H, G, S
standard temperature and pressure
- 0 degrees C (273K)
- 1 atm
used for ideal gas calculations
what is the standard state of a substance
the most stable state of the substance under standard conditions
evaporation/vaporization
liquid to gas phase change
molecules near the surface of liquid have enough kinetic energy to escape into the gas phase
condensation
gas to liquid phase change
molecules are forced by a lower temperature or higher pressure back into the liquid phase
fusion/melting
solid to liquid phase change
molecules in the solid absorb enough energy to break into liquid phase
solidification/crystallization/freezing
liquid to solid phase change
sublimation
solid to gas phase change
deposition
gas to solid phase change
triple point
point at which three boundaries meet on a phase diagram
critical point
point at which the phase boundary for liquid and gas terminate
(no distinction between the phases at this point)
what does temperature measure
average kinetic energy of particles of a substance
what does heat measure
transfer of energy from one substance to another as a result of difference in temperature
endothermic process delta Q
delta Q > 0
system absorbs heat
exothermic process delta Q
delta Q < 0
system releases heat
calorimetry
the process of measuring transferred heat
equation for heat absorbed/released in a process
q = mcdelta T
heat = mass * specific heat * change in temperature
specific heat (c)
amount of energy required to raise the temperature of one gram of substance by one degree C or K
equation for heat capacity
m*c
equation for heat absorbed/released during a phase change
q = m*L
heat = mass * latent heat
latent heat
enthalpy of an isothermal process
what does changes in enthalpy represent for a reaction
changes in heat at constant pressure
equation for delta H of a reaction
delta H rxn = H products - H reactants
endothermic process delta H
positive
products have more heat than reactants
heat is absorbed in reaction
exothermic process delta H
negative
products have less heat than reactants
heat is expressed in reaction
standard element of formation
enthalpy required to produce one mole of a compound from its elements in their standard states
standard enthalpy of a reaction
enthalpy change accompanying a rxn being carried out under standard conditions.
delta H rxn at standard conditions
Hess’s Law
state function changes of a reaction are additive
ENTHALPY, ENERGY, GIBBS FREE ENERGY
bond dissociation energy
average energy that is required to break a particular bond type
standard heat of combustion
enthalpy change associated with the combustion of a fuel
what does changes in entropy measure
spontaneous dispersal of energy at specific temperature
equation for entropy
delta S = Qrev / T
change in entropy = heat gained/lost in reversible process / T in kelvin
units of entropy
J / mol * K
units of enthalpy
J * mol
what does Gibbs free energy measure
maximum amount of energy released by a process occurring at a constant temp and pressure that is available to perform work
equation for Gibbs free energy
delta G = delta H - [T*delta S]
free energy = enthalpy - temp * entropy
goldfish are horrible without tartar sauce
exergonic reactions
- move toward eq’ position
- decrease in free energy
- releases energy
- spontaneous
endergonic reactions
- move away from eq’ position
- increase in free energy
- absorb energy
- non spontaneous
negative delta G
spontaneous
positive delta G
nonspontaneous
zero delta G
equilibrium
delta H = T*delta S
when is delta G temperature dependent
when delta S and delta H have the same sign
