Flashcards in General Chemistry-Thermochemistry Deck (190)
How do you determine if a process will be spontaneous or nonspontaneous?
Calculating the change in the Gibbs free energy (/\G) for a process, such as a chemical reaction.
What are temperature dependent processes?
The process will be temperature dependent, that is spontaneous at some temperatures and nonspontaneous at others.
What is a common method for supplying energy for nonspontaneous reactions?
Coupling nonspontaneous reactions to spontaneous ones.
What are macroscopic properties?
Properties that describe the system in an equilibrium state.
What is another name for macroscopic properties?
What can macroscopic properties not describe?
The process of the system; that is, how the system got to its current equilibrium.
Macroscopic properties can compare what?
One equilibrium state to another
What are process functions?
The pathway taken from one equilibrium state to another
What are the most important process functions?
State function include what?
Internal energy (U)
Gibbs Free Energy (G)
When do state functions change?
When the state of a system changes from one equilibrium to another
Are state function independent of one another?
Not necessarilly, For example Gibbs free energy is related to enthalpy, temperature, and entropy
What are the standard conditions of systems with various temperatures, pressures, and equilibrium states?
25 degrees C. (298 K)
1 atm Pressure
1 M concentration
Is standard conditions the same as standard temperature and pressure?
What is standard temperature and pressure (STP)?
The temperature is 0 Degrees C (273 K)
1 atm Pressure
When are standard conditions used and when are STP conditions used?
Standard conditions are used for kinetics, equilibrium, and thermodynamics
STP are used for ideal gas calculations
What is standard state of a substance?
Under standard conditions, it is the most stable form a substance.
What is the standard state of important elements at standard conditions?
C (s, graphite)
When is it important to know the standard state of an element?
For thermochemical calculations, such as heats of reactions and heats of formation.
What are the names of the changes in enthalpy, entropy, and free energy that occur when a reaction take place under standard conditions? Symbols?
The Standard enthalpy (/\H degree)
Standard Entropy (/\S degree)
Standard Free energy changes (/\G degree)
What does the degree sign represent in the symbols of standard enthalpy, entropy and free energy changes?
Zero, as the standard state is used as the "zero point" for all thermodyamic calculations.
What are phase diagrams?
Graphs that show the standard and nonstandard states of matter for a given substance in an isolated system, as determined by temperature and pressure.
What are phase changes?
(Solid Liquid Gas)
What is important to know about phase changes?
They are reversible and an equilibrium of phases will eventually be reached at any given combination of temperature and pressure
What happens to H2O at 0 Degrees C and 1 atm?
Ice and water exist in equilibrium
How much water vapor is present when H2O reaches equilibrium in liquid and gas state?
3% water vapor by mass
Phase equilibrium is analogous to what?
The dynamic equilibria of reversible chemical reaction: the concentrations of reactants and products are constant because the rate of the forward and reverse reactions are equal.
Temerpature of a substance in any phase is related to what?
The average kinetic energy of the molecules that make up a substance
What is evaporation?
Some of the molecules near the surface of the liquid may have enough kinetic energy to leave the liquid phase and escape into the gaseous phase.