Ch. 7: Thermochemistry Flashcards
Classification of Systems:
Isolated Systems
Closed Systems
Open Systems
Isolated: Exchange neither matter nor energy w the environment
Closed: Can exchange energy but not matter w the environment
Closed: Can exchange both energy and matter w the environment
Characterization of process based on single constant property
Isothermal: occur at a constatnt temp
Adiabatic: exchange no heat w the environment
Isobaric: occur @ constant pressure
Isovolumetric (isochoric): occur at a constant volume
State functions
Describe the physical properties of an equilibrium state; they are pathway independent and include pressure, density, temp, volume, enthalpy, internal energy, Gibbs free energy, and entropy
Standard conditions
Defined as 298 K, 1 atm, and 1 M concentrations
Standard State
Of an element is its most prevalent form under standard conditions
- Standard enthalpy, standard entropy, and standard free energy are all calculated under standard conditions
Phase Changes:
Exist at characteristic temps and pressures
Fusion and Freezing
Fusion (melting) and Freezing (crystallization or solidification) occur at the boundary between the solid and liquid phases
Vaporization and Condensation
Vaporization (evaporation or boiling) and condensation occur at the boundary between the liquid and the gas phases
Sublimation and Deposition
Occur at the boundary between solid and gas phases
Critical Point
At temps above the critical point the liquid and gas phases are indistinguishable
Triple Point
All three phases of matter exist in equilibrium
Phase diagram
For a sys graphs the phases and phase equilibria as a function of temp and pressure
Temperature
Scaled measure of avg kinetic energy of a substance
Heat
Transfer of energy that results from differences of temp between two substances
Heat content of a system
Undergoing heating cooling, or phase changes is the sum of all of the respective energy changes
Enthalpy
Measure of the potential energy of a system found in intermolecular attractions and chemical bonds
Hess’s law
States that the total change in potential energy of a system is equal to the changes of potential energies of the individual steps of the process
Enthalpy calculation
Can be calculated using heats of formation, heats of combustion, or bond dissociation energies
Entropy
Measure of the degree to which energy has been spread throughout a syste or between a system and its surroundings
- Ratio of heat transferred per mole per unit kelvin
- Maximized at equilibrium
Gibbs Free Energy
Derived from both enthalpy and entropy values for a given system
Change in Gibbs Free Energy
Determines whether a process is spontaneous or nonspontaneous
🔺G < 0; reaction proceeds in forward direction (spontaneous)
🔺G = 0; reaction is in dynamic equilibrium
🔺G > 0; reaction proceeds in reverse direction (nonspontaneous)
Temperature Dependence
Gibbs free energy depends on temperature; temperature-dependent processes change between spontaneous or nonspontaneous, depending on the temp
