Chapter 17: Thermodynamics Flashcards
What is the spontaneity of the process when the change in entropy of the system is greater than 0 and the change in entropy of the surroundings is greater than one?
The process is always spontaneous
Both positive no worry
What is the spontaneity of the process when the change in entropy of the system is less than 0 and the change in entropy of the surroundings is greater than one?
Spontaneous if the absolute value of the change in entropy of the system is less than the absolute value of the change in entropy of the surrounding
Non-spontaneous if the absolute value of the change in entropy of the system is greater than the change in entropy of the surroundings
* Temperature of surrounding is greater than that of the system in an exothermic process (freezing)
water put in freezer
What is the spontaneity of the process when the change in entropy of the system is greater than 0 and the change in entropy of the surroundings is less than one?
Spontaneous if the absolute change in entropy of the system is greater than the absolute change in entropy of the surroundings
Non-spontaneous if the absolute value of the change in entropy of the system is less than that of the surroundings.
*temperature of surrounding is greater than that of system in an endothermic process (melting)
What is the spontaneity of the process when the change in entropy of the system is less than 0 and the change in entropy of the surroundings is less than one?
The process is always non-spontaneous
Both negative there is nothing you can do
What is a spontaneous process?
A process that occurs without external intervention (air out of tire)
Disorder of energy
What is a non-spontaneous process?
A process that only occurs if energy is continually added to the system (air into tire)
Order of energy
What does spontaneity depend on?
The dispersion of energy, the entropy, that occurs during a process.
What is the molecular motion across the phases? How does the increase or decrease of molecular motion relate to kinetic energy and entropy?
Solid: vibrational motion (not much motion)
Liquid: translational
Gas: translational & rotational
As molecular motion increases so does kinetic energy and entropy
Define entropy:
The measure of how dispersed energy is in a system at a specific temperature.
The energy distribution affected by molecular motion and volume.
What is the second law of thermodynamics?
The total entropy of the universe increases in any spontaneous energy.
Change in entropy of universe = change in entropy of system + change in entropy of surroundings.
What is an isothermal process?
Reversible process{ a process that can be run in reverse and no net energy has flowed to system or surroundings. (ie flow of heat, q)
What is the difference between H and q?
There is no difference between H and q. H is q for a certain process (i.e. melting or freezing)
What is q rev and how does it relate to entropy?
It is the flow of heat in a reversible reaction. Change in entropy = q rev / Temperature
At what temperature does all molecular motion cease and entropy equal zero?
At absolute zero
What is the third law of thermodynamics?
The entropy of a perfect crystal is zero at absolute zero.
What is the standard molar entropy?
S*, the absolute entropy of one mole of a substance in its standard state at 298K and one bar of pressure.
Calculated from measurement of molar heat capacities as a function of temperature
How does entropy relate to the structure of a molecule?
Entropy increases with increasing complexity of structure.
(more bonds more opportunities for internal motion)
CH4–> CH3CH3 –> CH3CH2CH2CH3
How do you calculate the entropy change for the system?
Change in standard molar entropy of a rxn = the sum of n products * molar entropy products - sum of n reactants * molar entropy reactants.
What is Gibbs Free Energy?
(G) the Maximum energy released by a process occurring at constant temperature and pressure that is available to do useful work.
How is G calculated from the change in entropy of the universe?
ASuni = ASsys + ASsurr
ASuni = ASsys - AHsys/T
-TASuni = - TASsys + AHsys
AG = AH - TAS
The change in Gibbs Free energy equals the negative temperature times the change in entropy of the universe.
What are the driving forces that contribute to spontaneity?
The system experiences an increase in entropy: ASrxn > 0
The process is exothermic: AHrxn < 0
What does the Gibbs free energy reaction relate?
It relates enthalpy, entropy, and temperature for a process.
How is the change in standard molar Gibbs free energy calculated?
The change in standard molar Gibbs free energy of a reaction = the sum of the n product * the change in standard molar Gibbs free energy products - the sum of the n reactant * change in standard molar Gibbs free energy reactants
What is free energy?
Energy available to do useful work
What can the change in internal energy of a system be used for?
It can be used to perform work: AE = q + w
How can thermodynamic efficiency be calculated?
(Work done) / (energy produced)
What is the change in enthalpy is negative and the change in entropy is positive what is the change in G and what is the spontaneity of the system?
The change in G will always be less than zero and the reaction will be always spontaneous
What is the change in enthalpy is negative and the change in entropy is negative what is the change in G and what is the spontaneity of the system?
The change in G will be less than zero at lower temperatures and the process will be spontaneous at lower temperatures–ice freezes at lower temperatures
What is the change in enthalpy is positive and the change in entropy is positive what is the change in G and what is the spontaneity of the system?
The change in G will be less than zero at higher temperatures and the process will be spontaneous at higher temperatures. (Ice melt at higher temperatures)
What is the change in enthalpy is positive and the change in entropy is negative what is the change in G and what is the spontaneity of the system?
The change in G will always be greater than zero. Process will never be spontaneous
How is Q verses K related to AG?
Q=K AGrxn = 0, system is at equilibrium
Q<K AGrxn < 0 the system will proceed spontaneously in the forward direction
Q>K AGrxn > 0 the system will proceed spontaneously in the revers direction
How are AG and K related?
AG < 0; K is large, favors products
AG slightly < 0; K slightly favors products
AG > 0; K «_space;1, favors reactants
May not be true in standard conditions
What will the slope of a reaction be if the reaction is exothermic, is endothermic?
Exothermic: positive slope (b/c AH -)
Endothermic: negative slope (b/c AH +)
What is the equation
ln(K2/K1)=-AH*/R(1/T2-1/T1) used for?
To find initial and final temperatures.
What does the degree symbol mean?
Standard conditions 298.15K
