Kaplan Chemistry: Chapter 7 Thermochemistry Flashcards
Change in internal energy system
delaU = Q-W Q = heat W = work done BY system
what does U equal in an isothermal process.
isothermal process = constant temp, meaning that U is CONSTANT.
deltaU = 0 = Q-W
therefore, Q = W
what does the area in a P vs V graph signify
the work done by the system, and the heat that entered the system
in an adiabatic process, what is delta U equation?
adiabatic: no heat is exchanged. therefore, Q=0, meaning that deltaU=-W
in a P vs V graph, and adiabatic process appears to be:
hyperbolic
what does a P vs V graph look like in an isobaric process?
isobaric = pressure is constant. isobaric processes are horizontal lines.
what does a P vs V graph look like in an isochoric process?
isochoric = isovolumetric = constant volume. W =0. therefore, deltaU = Q –> change in interanl energy is equal to the heat added to the system.
- in a P vs V graph, an isovolumetric processes causes a VERTICAL LINE, meaning that the WORK is 0 because work is the area of a Pvs V graph.
state functions
Pressure, Density, temperature, volume, enthalpy, internal energy (U), free energy (G), and entropy (S)
standard conditions
25C (298K), 1atm pressure, 1M concentrations.
when are standard conditions used?
kinetics, equilibrium, and thermodynamic problems
STP conditions
0C (273K), 1 atm pressure.
when are STP conditions used?
used for ideal gas calculations.
entropy and enthalpy ____ with temperature
INCREASES with temperature
entropy and enthalpy ____ as a material changes phase from solid –> liquid –> gas
increases.
sublimation means
solid to gas, by passes liquid stage
deposition means
gas to solid, by passes the condensation to liquid stage.
true definition of enthalpy
heat (Q) under a constant pressure, which is an assumption that is usually made for thermodynamic problems.
equation for heat absorbed or released in a given process
Q = mcdeltaT
units for a newton
kgm/s^2
units for a joule
1J = Nm = (kgm^2)/s^2
heat of a substance when it is undergoing a phase change
q=mL
L= latent heat capacity.
temp remains constant as the compound is converted to the next phase. once the entire sample is converted, then the temperature begins to rise again.
enthalpy/heat changes at a constant pressure equation
delta H = H(products)-H(reactants)
enthalpy of formation of pure elements
0
what is the standard heat of reaction? formula?
the enthalpy change accompanying a reaction being carried out under standard conditions
deltaHrxn = sumHformation(products)- sumHformation(reactants)
Hess’s Law and equation
enthalpy changes of reactions are additive
delta Hrxn = HbondsBROKEN - Hbondsformed.
longer hydrocarbons produce more combustion products and release ____ heat.
release more heat. that is, longer hydrocarbon combustion is more exothermic.
Entropy formula in relation to Q and temperature
S = Q/T Q = heat that is gained or lost in a reversible process.
Gibbs free energy equation involving H, T and S
G = H - TS
if H is -, and S is +, the reaction is ____ (spon/nonspon)
spontaneous
if H is +, and S is -, the reaction is ____ (spon/nonspon)
NEVER spontaneous
if H is -, and S is -, the reaction is ____ (spon/nonspon)
spontaneous at LOW temp
if H is +, and S is +, the reaction is ____ (spon/nonspon)
spontaneous at HIGH TEMP
what does it mean when deltaG is 0
the reaction is in equilibrium.
equation for gibbs free energy when the reaction is not taking place under standard state.
G = Go + RTlnKeq
recall: Go = -RTlnKeq
The relative thermodynamic stability of isomeric organic compounds can be inferred from which of the following types of experimental data?
A.Boiling points
B.UV–visible absorption spectra
C.Mass spectroscopic fragmentation patterns
D.Heats of combustion
Heats of Combustion
The question stem is asking about thermodynamic stability, or chemical energy. This has to do with how stable the bonds are IN the molecule.
Boiling point only tells you how tightly the molecule “holds onto” other molecules of its kind. It is a physical, not a chemical, property. Boiling point is INTERmolecular, thermodynamic stability is INTRAmolecular.
The question is asking about the quality of the compounds themselves, so you shouldn’t be thinking about a property that requires more than one molecule (like boiling point).
