Chapter 16 Thermodynamics Textbook Flashcards
A spontaneous process
one that occurs naturally under certain conditions
A nonspontaneous process will not take place unless
will not take place unless it is “driven” by the continual input of energy from an external source
A process that is spontaneous in one direction under a particular set of conditions is —- in the reverse direction
nonspontaneous
The spontaneity of a process is not correlated to the —-
speed of the process.
A spontaneous change may be so rapid that it is essentially instantaneous or so slow that it cannot be observed over any practical period of time.
kinetically stable+ex
If the activation energy is high, the reaction is kinetically stable.
If it is not able to change forms in a short time (Ex: Dimonds to graphite takes long time so its kinectically stable.
thermodynamically unstable
There exists a state where the system will have lower energy than it currently has. (spontaneous)
When two objects at different temperatures come in contact, heat spontaneously flows from
the hotter to the colder object.
graphitization
The conversion of carbon from the diamond allotrope to the graphite allotrope
The phase diagram indicates that
graphite is the stable form of this element under ambient atmospheric pressure, while diamond is the stable allotrope at very high pressures, such as those present during its geologic formation.
Diamonds are said to be
diamonds are said to be thermodynamically unstable but kinetically stable under ambient conditions.
Two flask connected by a closed valve, tell me about the work, heat, internal energy, and what is sponetatey not a consequence of? (4)
- The work is 0 because pressure in a vaccum is zero.
- The heat is 0 since the system is isolated
- The first law of thermodynamics confirms that there has been no change in the system’s internal energy as a result of this process.
- The spontaneity of this process is therefore not a consequence of any change in energy that accompanies the process.
What is the driving force of the spontaneity of the 2 valve process? (2)
Initially…..
- greater, more uniform dispersal of matter that results when the gas is allowed to expand
- Initially, the system was comprised of one flask containing matter and another flask containing nothing. After the spontaneous expansion took place, the matter was distributed both more widely (occupying twice its original volume) and more uniformly (present in equal amounts in each flask).
an important factor in determining the spontaneity of a process is—— for example——
- the extent to which it changes the dispersal or distribution of matter and/or energy
- a spontaneous process took place resulted in a more uniform distribution of matter or energy.
reversible process
one that takes place at such a slow rate that it is always at equilibrium and its direction can be changed (it can be “reversed”) by an infinitesimally small change in some condition.
entropy (S)+formula with heat+what it is (3)
-State function
-Engery. unable to do work
*heat divided by temperature
Low entropy
energy is concentrated
High entropy
Energy is spread out
microstate (2)
a specific configuration of all the locations and energies of the atoms or molecules that make up a system
The arrangement of each molecule in the system at a single instant.
The relation between a system’s entropy and the number of possible microstates is
where k is the Boltzmann constant, 1.38 10^−23 J/K.
The most probable distribution is the one with
*Not entropy
the most mircostates
CHANGE in entropy formula
When entropy increases what happens to final/initial/microstates/ΔS ?
For processes involving an increase in the number of microstates, Wf > Wi, the entropy of the system increases and ΔS > 0.
Conversely, processes that reduce the number of microstates, Wf < Wi, yield a
decrease in system entropy, ΔS < 0
Processes that reduce the number of microstates Wf < Wi, yield a
yield a decrease in system entropy, ΔS < 0
The most probable distribution is therefore the
one of greatest entropy.
The probability that a system will exist with its components in a given distribution is
proportional to the number of microstates within the distribution
As you add more particles to the system, the number of possible microstates increase
exponentially (2^N)
Why increase in temp means more microstates?
At higher temperature, the wider range of accessible kinetic energies leads to more microstates for the system.
The reason systems tend toward higher entropy states is simply that… (2)
- those states are more probable
- more likely to exist from the myriad of possible states. These states contain distributions of molecules and energies that are the most probable. What distributions are the most probable? The ones with the greatest number of microstates. A microstate is a specific way in which we can arrange the energy of the system. Many microstates are indistinguishable from each other. The more indistinguishable microstates, the higher the entropy.
*Imagine all the gas molecules in the room you are sitting in. Now in your mind divide the room into two sides (left and right). Each molecule (which is carrying some amount of energy) could be anywhere in that room. Each molecule has a 50/50 chance of being either on the right side or the left side of the room. What are the odds that all of the molecules (and there are a whole lot of them) are on the right side of the room. The chances are not just small. They are so small that we don’t have to worry about this ever happening. What are the odds that the molecules are essentially evenly distributed between both sides of the room. The odds are astronomically large. So large that we can be assured that this is how we will find the molecules. That is the essence of the microscopic view of entropy. There are fewer ways to arrange the molecules and have them all on one side of the room. Fewer microstates = low entropy. There are more ways to arrange the molecules and have them evenly distributed. More microstate = more entropy.
Microstates in which all the particles are in a single box are the most ordered, thus possessing the — entropy
least
Microstates in which the particles are more evenly distributed among the boxes are more disordered, possessing —- entropy.
greater
Tell me about microstates of solids and liquids
+Whats the equality/inequality statement?
In the solid phase, the atoms or molecules are restricted to nearly fixed positions with respect to each other and are capable of only modest oscillations about these positions. With essentially fixed locations for the system’s component particles, the number of microstates is relatively small. In the liquid phase, the atoms or molecules are free to move over and around each other, though they remain in relatively close proximity to one another. This increased freedom of motion results in a greater variation in possible particle locations, so the number of microstates is correspondingly greater than for the solid.
freezing exhibits a —— in entropy,
decrease
ΔS < 0.
Why entropy of gas so big?
Each atom or molecule can be found in many more locations, corresponding to a much greater number of microstates
According to kinetic-molecular theory, the temperature of a substance is proportional to the
average kinetic energy of its particles.
Why does temperature increase entropy? (2)
Raising the temperature of a substance will result in more extensive vibrations of the particles in solids and more rapid translations of the particles in liquids and gases. At higher temperatures, the distribution of kinetic energies among the atoms or molecules of the substance is also broader (more dispersed) than at lower temperatures. Thus, the entropy for any substance increases with temperature
The higher the temperature the more thermal energy the system has; the more thermal energy the system has, the more ways there are to distribute that energy; the more ways there are to distribute that energy, the higher the entropy. Increasing the temperature will increase the entropy.
heavier atoms possess —– entropy at a given temperature than lighter atoms bc……
greater
Molecules with more “parts,” such as electrons, protons, and other atoms bonded, have more possible orientations and vibrations than simpler molecules. This means they have more entropy.
Compared to a pure substance, in which all particles are identical, the entropy of a mixture of two or more different particle types is —. This is because of the….
- greater
- additional orientations and interactions that are possible in a system comprised of nonidentical components
In thermodynamic models, the system and surroundings comprise everything, that is, the universe, and so the following is true:
Second law of thermodynamic
all spontaneous changes cause an increase in the entropy of the universe.
For a process at constant T and constant P we can rewrite the equation for Gibbs free energy in terms of
When
ΔG<0 (2)
+What is the process called and what will happen to the reaction?
the process is exergonic and will proceed spontaneously in the forward direction to form more products.
When
ΔG>0
+What is the process called and what will happen to the reaction?
the process is endergonic and not spontaneous in the forward direction. Instead, it will proceed spontaneously in the reverse direction to make more starting materials.
When
ΔG=0
+What is the process called and what will happen to the reaction?
the system is in equilibrium and the concentrations of the products and reactants will remain constant.
the reaction is…
spontaneous
The reaction is
nonspontanous
*spontaneous in opposite direction
The reaction is
at equilibrium
The entropy of a pure, perfectly crystalline solid possessing no kinetic energy (that is, at a temperature of absolute zero, 0 K is:may be described by …… the entropy of this system is
- a single microstate
- zero
Third law of thermodynamics
the entropy of a pure, perfect crystalline substance at 0 K is zero.
Standard entropies
The entropy for one mole of substance under standard conditions (a pressure of 1 bar and a temperature of 298.15 K)
Equations for entropy: (2)
1. Boltzmann equation. 2. Heat
S=q/T
The standard entropy change (ΔS°) for a reaction may be computed by…
not ln one or q
Where v=stoichiometric coefficients in the balanced equation
One of the challenges of using the second law of thermodynamics to determine if a process is spontaneous is that it
requires measurements of the entropy change for the system and the entropy change for the surroundings.
Gibbs free energy (G)
+formula only
Free energy is a
state function
Free energy at constant temp and pressure can be expressed as:
Relating to the second law of thermodynamics equation, Gibbs free energy can be expressed as:
The relationship between this system property and the spontaneity of a process may be understood by recalling the previously derived second law expression:
The first law requires that qsurr = −qsys, and at constant pressure qsys = ΔH, so this expression may be rewritten as:
Multiplying both sides of this equation by −T, and rearranging yields the following:
Gibbs free energy (G) is more convient because it , allows us to
avoid calculating the entropy of the surroundings
So what exactly is free energy?
the amount of useful energy present in a thermodynamic system that can be utilised to perform some work
When we do Gproduct-Greactant,
we are measuring if the product had less energy then the reactants. Since life favours lower energy state having neg means its “natural” or spontaneous
Chemists normally measure energy (both enthalpy and Gibbs free energy) in…. but entropy in…..
kJ mol^-1 (kilojoules per mole) but measure entropy in J K^1 mol-1 (joules per kelvin per mole)
crossover point is when ΔG is zero, how do we find when this is?
When we calculate the enthalpy of a reaction given the individual moleculae one how do we do this?
Aside from entropy and enthalpy, standard free energy change for a reaction may also be calculated from
standard free energy of formation ΔGf° values of the reactants and products involved in the reaction.
standard free energy of formation ΔGf° (4)
+What it is+conditions+elemental+formula
- the free energy change that accompanies the formation of one mole of a substance from its **elements **
-Standard Gibbs free energy of formation is the change in Gibbs free energy when elements in their standard states combine to form a product also in its standard state. - in their standard states
- Similar to the standard enthalpy of formation, is by definition zero for elemental substances in their standard states.
When can we use the individual atom/molecule to compute the reaction’s overall value?
Entropy, Enthalpy and free energy bc they are state functions
The free energy change for the sum reaction is
the sum of free energy changes for the two added reactions
Coupled reaction for free energy why is this important? +ex
a nonspontaneous reaction is enabled by coupling it to a spontaneous reaction
To illustrate, the production of elemental zinc from zinc sulfide is thermodynamically unfavorable, as indicated by a positive value for ΔG°. By coupling this decomposition reaction to the thermodynamically favorable oxidation of sulfur, we can produce zinc!
The coupled reaction exhibits a negative free energy change and is spontaneous:
If I want the change in Gibbs’s free energy for the reverse reaction, I….
Multiply by neg sign
Both ΔH and ΔS are positive
+Explain whats happening+is this spontaneous or not
- This condition describes an endothermic process that involves an increase in system entropy. In this case, ΔG will be negative if the magnitude of the TΔS term is greater than ΔH. If the TΔS term is less than ΔH, the free energy change will be positive. Such a process is spontaneous at high temperatures and nonspontaneous at low temperatures.
Both ΔH and ΔS are negative.
+Explain whats happening+is this spontaneous or not
This condition describes an exothermic process that involves a decrease in system entropy. In this case, ΔG will be negative if the magnitude of the TΔS term is less than ΔH. If the TΔS term’s magnitude is greater than ΔH, the free energy change will be positive. Such a process is spontaneous at low temperatures and nonspontaneous at high temperatures.
ΔH is positive and ΔS is negative
+Explain whats happening+is this spontaneous or not
This condition describes an endothermic process that involves a decrease in system entropy. In this case, ΔG will be positive regardless of the temperature. Such a process is nonspontaneous at all temperatures.
ΔH is negative and ΔS is positive
+Explain whats happening+is this spontaneous or not
This condition describes an exothermic process that involves an increase in system entropy. In this case, ΔG will be negative regardless of the temperature. Such a process is spontaneous at all temperatures.
So, saying a process is spontaneous at “high” or “low” temperatures means the temperature is above or below, respectively, that temperature at which ΔG for the process is
zero
So, saying a process is spontaneous at “high” or “low” temperatures means the temperature is above or below, respectively, that temperature at which ΔG for the process is
zero
The formula for the temperature point that dictates if a reaction is spontaneous or not
These plots show the variation in ΔG with temperature for the four possible combinations of arithmetic sign for ΔH and ΔS.
When When ΔG is zero (2)
drivinf force, what is happenening?
- the forward and reverse driving forces are equal
- The process occurs in both directions at the same rate (the system is at equilibrium).
What is the conditions to use this equation?
The free energy change for a process taking place with reactants and products present under nonstandard conditions (pressures other than 1 bar; concentrations other than 1 M
For a system at equilibrium, the free energy cant be calculate by ….. and is….
In this case,…
Composition of an Equilibrium Mixture….
Products are more abundant
When you have an equilibrium equation, and they ask for the free energy of solubility for agcl
isnt just the product’s free energy you find in the book. You see what its asking you to find (ex: the solubility constant of the a salt that dissociate into ions and back again) and calculate free energy by product-reactant
