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)
