Chapter 7- Thermochemistry Flashcards
First law of thermodynamics
Change in U = Q - W
U= change in internal energy of system (directly proportional to temperature) Q= heat added to system W= work done by system
Isothermal
Constant temperature
Adiabatic
No heat exchanged between system and environment
Isobaric
Pressure is constant of a system
Isovolumetric
Aka isochoric. Experience no change in volume (neither expand nor compress) no work is done.
Standard conditions
25C (298K), 1atm, 1M concentrations
*used for measuring standard S, H, G, and electrochemical cell voltage
Standard temperature and pressure (STP)
0C (273K) and pressure is 1atm
*used for gas law calculations
Sublimation
Solid to gas
Deposition
Gas to solid
Critical point
No distinction between phases for this temp and pressure. (Supercritical fluids)
Zeroth law of thermodynamics
Objects are in thermal equilibrium only when their temperatures are equal
Enthalpy
(H) equivalent of heat under constant pressure. State function so path doesn’t matter for value.
+ endothermic
- exothermic
Calorimetry
Process of measuring transferred heat
Equation if no work is done
Qsystem = -Qsurroundings
When does the temperature change with respect to a phase change
The temperature stays the same until the whole compound changes phase. No temp change during freezing, melting, condensation, or vaporization until the process is complete.
Heat still changes during phase changes even tho temp does not. How do you calculate the heat change if temp change is zero?
With enthalpy
q = mL
m-mass
L- latent heat (general for enthalpy)
Second law of thermodynamics
Energy spontaneously disperses from being localized to becoming spread out if it’s not hindered from doing so. (Entropy)
Entropy equation
(S) = Qrev / T
Qrev- heat gained or lost in reversible process
Entropy increase vs decrease
Increase- energy distributed into a system
Decrease- energy distributed out of a system
Gibbs free energy equation
🔺G = 🔺H - T🔺S
Toward equilibrium means lower Gibbs (goal is lowest Gibbs)
🔺G -, +, and 0
- spontaneous
+ nonspontaneous
0 state of equilibrium
Standard free energy change equation
🔺G = -RT ln(Keq)
The larger Keq the more spontaneous the reaction
Free energy change equation (not at standard state)
🔺G = RT ln(Q/Keq)
Hear transfer during phase change
q = mL
Spontaneous process moving in the forward direction
🔺GQ
Endergonic vs exergonic
They both describe Gibbs free energy.
Exergonic- release energy, spontaneous, 🔺G>0
