7. Thermodynamics Flashcards
Know to find solid, liquid, gas, sublimation/deposition, melting/freezing, condensation/vaporization in phase diagram. What’s the triple point vs critical point?
phase change on lines, states of matter on spaces (left to right: solid, liq, gas)
all phases simul vs no distinction between phases: liquid evap at super fast rate –> density of liq and gas = same => supercritical fluid
temp on x axis and pressure on y axis
Know how to read a heating curve
phases on slants, phase changes on flat lines (all phase changes = isothermal ie. no temp change at all), y-axis = temp, x-axis = heat added
What are the 0th vs 1st vs 2nd laws of thermodynamics?
transitive property with thermal equil; heat transfers from hot to cold vs energy cannot be created nor destroyed vs entropy inc spontaneously
High vapor pressure means…
It REALLY wants to evaporate (ex: CO2; Fe has low vapor pressure)
usually lighter molec, high KE
How does inc/dec temp affect exothermic rxns?
Inc temp shifts to left, dec temp shifts to right
How do you know if there’s more entropy in a rxn?
Look at phase changes or moles; look to see if products are MORE ORDERLY (ex: dimer formation = dec in entropy)
What does system do w/ heat for endothermic vs exothermic?
system absorbs heat vs system releases heat
Isothermal vs adiabatic vs isobaric vs isovolumetric/isochoric
Temp of system is constant (looks like a shallow curve on P-V graph) vs no heat exchange occurs (looks hyperbolic or deeper curve on a P-V graph) vs pressure of system is constant vs volume of system is constant
Bond enthalpy formula
DeltaH0rxn = sum(deltaH) for bonds broken minus sum(deltaH) for bonds formed
Bond dissociation energy aka bond enthalpy
THE ENERGY IT TAKES TO BREAK SPECIFC BONDS IN A GAS PHASE; NEEDING ENERGY TO BREAK A BOND IS ENDOTHERMIC. BDE ITSELF = ALWAYS A POS VALUE! (So don’t confuse BDE with DeltaH0rxn b/c DeltaH0rxn could be neg if you calculate it)
This means forming a bond releases energy —> exothermic
Entropy of univ formula
DeltaS for universe = deltaS for system + deltaS for surroundings > 0
Entropy of system can dec if entropy of surroundings inc by same amount. In an isolated system, entropy always inc
If deltaG = 0, system in in equil. What does it mean for deltaH and TdeltaS?
DeltaH = TdeltaS
Relationship with deltaU = Q - W. And know the relations in adiabatic, isothermal and isovolumetric processes
pos deltaU = inc temp; neg deltaU = dec temp
pos Q = heat flows into system; neg Q = heat flows out of system
pos W = work is done by system => expansion; neg W = work is done on system => compression
State functions vs process functions
Describes a system in equil state (ex: pressure, density, temp, vol, heat/enthalpy, internal energy, Gibbs free energy, entropy) vs describes how a systems reached equil quantitatively (ex: Q and W)
Standard conditions vs STP
1 M, 1 atm, 25°C aka 298 K vs 0°C aka 273 K, 1 atm
What’s enthalpy?
deltaH, pos = endothermic and neg = exothermic. Same thing as Q but under constant pressure
What’s the specific heat capacity? What’s its value for water?
1 cal/gK or 4.184 J/gK
Amount of heat required to raise temp of one mass unit by 1 degree C or 1 K. INVERSE TO DELTAT
Examples of constant-pressure calorimeter vs constant-volume calorimeter
Coffee cup vs bomb calorimeter/decomposition vessel
Calorimeter is suppose to be an isolated system but when it’s not sealed correctly, it’ll be an open system
How to find heat energy during a phase change?
q = mL
L - in cal/g; heat of transformation or latent heat of substance; represents enthalpy of isothermal process
Enthalpy of fusion vs vaporization
Enthalpy at solid/liquid change vs liq/gas change
Standard heat of formation formula
DeltaH0 = sumn(deltaHf0) of products - sumn(deltaHf0) of reactants
n = mol DeltaHf0 = standard enthalpy of formation (amount of heat lost or gained in a rxn); usually given, but know that standard enthalpy of formation for any element in standard state = zero
Entropy formula of a reversible process
DeltaS = Qrev/T
DeltaS=change in entropy
Qrev=heat that’s gained or lost in a reversible process
T=temp in K
DeltaG for anabolic vs catabolic rxns
> 0 vs < 0
Hess’ Law
Enthalpy change = same for a rxn consisting of a single step or multiple steps. 2 ways to manipulate to match the rxn you’re looking for: flip rxn (you also have to flip sign of given deltaH) or multiply by constant (you also have to multiply that same constant to given deltaH)
Most NEG change in enthalpy and entropy means?
Least change
Why is temp necessary for phase change?
To overcome intermolecular forces
Kinetic vs thermodynamic product
Lower Ea needed —> forms faster, get it at low temps, ends with higher deltaG compared to thermodynamic product —> less stable product; IRREVERSIBLE vs high Ea needed —> forms slower, get it at high temps, ends with lower deltaG than kinetic product —> more stable product; REVERSIBLE
The most neg rate of combustion means…?
Reactants have more energy than products —> less stable
What kind of rxn vessel is best to do rxns?
low thermal conductivity (we want rxn vessel to be insulating), low thermal expansion (we don’t want rxn vessel to expand and break under high temps), high melting pt (we want rxn vessel to w/stand lots of heat if a rxn = exothermic)
