Chemistry 1212 Exam #4 Lecture Notes/Mastering Concepts
spontaneity
(delta) G is a measure of_____
work
(delta)G is a measure of_____
zero
(delta)G of an element equals____
spontaneity
1st Law of Thermodynamics does NOT allow us to predict_______
not be suitable because ΔSuniv>0. *S is positive, making reaction spontaneous, and boiling would occur
A particular solvent with ΔS∘vap=112.9J/(K⋅mol) and ΔH∘vap=38.0kJ/mol is being considered for an experiment. In the experiment, which is to be run at 75 ∘C, the solvent must not boil. Based on the overall entropy change associated with the vaporization reaction, would this solvent be suitable and why or why not?
does NOT
A perfect crystal____ exist
postive (delta) S
All spontaneous processes will have a______
loses mass gains mass
Anode_____mass Cathode_____mass
SO3 > Cl2 > Kr
Arrange these gases in order of decreasing standard molar entropy: SO3 Kr Cl2
S (entropy) rises
As a molecule becomes more complex, ______rises
B. ΔG∘f=−33.30 kJ/mol D. ΔG∘f=−604.0 kJ/mol *Gf must be negative in order to be feasible
Based on the standard free energies of formation, which of the following reactions represent a feasible way to synthesize the product? A. ΔG∘f=102.6 kJ/mol B. ΔG∘f=−33.30 kJ/mol C. ΔG∘f=67.10 kJ/mol D. ΔG∘f=−604.0 kJ/mol
entropy and enthalpy
Both_____ and______ factor into the determination of a reactions spontaniety.
is the potential energy per unit charge that is characteristic of each half-cell reaction. It is measured in volts (V). 1 volt = 1 joule/coulomb (1 V = 1 J/C)
Cell potential:
spontaneity *only part of the spontaneous equation not the whole
Change in enthalpy (ΔH) of a process often seems to predict_______
(a) 1mol of SO3(g) - more atoms (b) 1mol of CO2(g) - gas > solid (e) 230C - higher temperature (f) CCl4 - larger mass
Choose the member with the higher entropy in each of the following pairs, and justify your choice [assume constant temperature, except in part (e)]: (a) 1mol of SO2(g) or 1mol of SO3(g) (b) 1mol of CO2(s) or 1mol of CO2(g) (e) Seawater in midwinter at 2 degrees Celsius or in midsummer at 23 degrees Celsius (f) 1mol of CF4(g) or 1mol of CCl4(g)
free energy change of a reaction according to the equation
Concentrations of reactants and products influence the_______
S(solid) < S(liquid) < S(gas) *S increases to less ordered phase
Describe entropy between phase changes
a single swing of a real pendulum - Irreversible solid melting infinitesimally slowly above its melting point - Irreversible liquid freezing below its freezing point - Irreversible gas condensing below its condensation point - Irreversible liquid vaporizing above its boiling point - Irreversible
Determine whether each of these processes is irreversible: 1) solid melting infinitesimally slowly at its melting point 2) a single swing of a real pendulum 3) gas condensing infinitesimally slowly at its condensation point 4) solid melting infinitesimally slowly above its melting point 5) liquid freezing below its freezing point 6) liquid freezing infinitesimally slowly at its freezing point 7) a single swing of a frictionless pendulum 8) liquid vaporizing infinitesimally slowly at its boiling point 9) gas condensing below its condensation point 10) liquid vaporizing above its boiling point
gas condensing infinitesimally slowly at its condensation point Solid melting infinitesimally slowly at its melting point liquid freezing infinitesimally slowly at its freezing point a single swing of a frictionless pendulum liquid vaporizing infinitesimally slowly at its boiling point
Determine whether each of these processes is reversible: 1) solid melting infinitesimally slowly at its melting point 2) a single swing of a real pendulum 3) gas condensing infinitesimally slowly at its condensation point 4) solid melting infinitesimally slowly above its melting point 5) liquid freezing below its freezing point 6) liquid freezing infinitesimally slowly at its freezing point 7) a single swing of a frictionless pendulum 8) liquid vaporizing infinitesimally slowly at its boiling point 9) gas condensing below its condensation point 10) liquid vaporizing above its boiling point
ΔG become more positive as the temperature increases. *Since the value of ΔS is negative, increasing the temperature of the reaction results in a more positive value of ΔG.
Does ΔG become more negative or more positive as the temperature increases?
use electrical energy to drive non-spontaneous rxt (Δ G > 0) *Surroundings do work on system *Lower energy reactants + electrical energy ---> higher energy products *Usually the chemical reaction is desired outcome
Electrolytic cells:
is the electrical driving force that "pushes" electrons from the oxidation half-cell to the reduction half-cell.
Electromotive force or emf (E) :
Eo ( cathode) - Eo ( anode)
Eo cell =
0; Keq **(delta)G degrees calculated from the data in Appendix G, can be used to calculate the value of the equilibrium constant.
For a system at equilibrium, (delta)G =____, and Q =_____
The molar entropy of a substance increases with increasing temperatures.
How does the molar entropy of a substance change with increasing temperature?
spontaneous
IF E cell is greater than 0:
(delta)S is positive! *(delta)G can be spontaneous when H is positive and S is positive
If (delta) Hrxn = +62.3 kJ and is spontaneous, is (delta)S negative or positive?
negative!
If G is negative and S is negative then what would H be?
By itself, no But reaction can occur if energy is supplied from another reaction
If a reaction is non-spontaneous will it ever occur?
G = 0 lnK=0 K=1
If there are equal amounts of products reactants in a mixture, what will G, K, and lnK be?
G < 0 lnK > 0 K > 1
If there are more products than reactants in a mixture, what will G, K, and lnK be?
G > 0 lnK < 0 K < 1
If there are more reactants than products in a mixture, what will G, K, and lnK be?
oxidation; reduction
In a half-reaction, either the_____ or _______ part of a redox reaction is given, showing the electrons explicitly.
Ecell is positive and E∘cell is negative.
In an electrochemical cell, Q = 0.0010 and K = 0.10. What can you conclude about Ecell and E∘cell?
conditions *goal is to predict spontaneity
In chemical systems direction depends on______
the left half-cell will decrease in concentration; and the right half-cell will increase in concentration.
Indicate what happens to the concentration of Pb2+(cathode) in each cell.
(Δ°Hrxn)--Exothermic (gives off 74.6 kJ of heat) (Δ°Grxn)--Max amount of energy available for work is 50.5 kJ (Gibbs) (Δ°Srxn)--Entropy of the system is negative Reaction is spontaneous Emitted heat increases entropy of surroundings enough to make net entropy of universe positive Gibbs is what remains after accounting for heat loss
Interpret this data: C(s, graphite) + 2 H2(g) ----> CH4(g) Δ°Hrxn = -74.6 kJ Δ°Srxn = -80.8 J/K Δ°Grxn = -50.5 kJ
reversible; spontaneously
Many chemical and physical processes are _______, but tend to proceed in one direction ______
lowest
Mechanical systems tend toward______potential energy
Exothermic *some are not
Most spontaneous reactions are (exothermic/endothermic)?
spontaneity
Negative values of (delta) H and positive values of (delta)S favor______
work; at least ∆G amount of work
Non-spontaneous reactions require_____ in order to occur. Each non-spontaneous reaction requires_____
added energy *does not mean it is impossible
Nonspontaneous requires______
*boiling of water is change from liquid to gas so entropy will increase; S is positive *gas to solid so entropy will decrease; S is negative * solid to gas so entropy will increase; S is positive
Predict the (delta)S for each process: boiling water I2(g)---> I2(s) CaCO3(s)----> CaO(s) + CO2(g)
*endothermic reaction-increase in entropy (+S),High temp for spontaneity *solid to gas increase in entropy (+S). High temp for spontaneity. *gas to liquid decrease in entropy (-S). Low Temp for spontaneity *bond breaking into more particles, increase entropy (+S), High Temp for spontaneity
Predict the conditions (high temperature, low temperature) in order to be spontaneous endothermic reaction solid to gas gas to liquid H2(g)--->2H(g)
increases
S (entropy)_______ as Temperature rises
quick *Catalysts can increase reaction rates *Nonspontaneous reactions cannot become spontaneous with a catalyst
Spontaneous does not necessarily mean_____
work; ∆G
Spontaneous reactions can do_____. The most work a reaction can do equals_____
is the cell potential when each species in the reaction is present in its standard state.
Standard potential, Ecell:
Spontaneous at low temperatures.
The condensation of water has a negative ΔH and a negative ΔS. What can you conclude about the spontaneity of the process?
from the T*(delta)S term
The dependence of (delta)G on Temperature arises mainly________
more easier reduction to occur/most favored
The more positive E knot cell:
ΔG∘rxn>0
The reaction A(g)⇌B(g) has an equilibrium constant that is less than one.What can you conclude about ΔG∘rxn for the reaction?
positive; less than 1
The standard cell potential, E∘, of a reaction is found to be −0.11 V. For this reaction, the value of ΔG∘ is expected to be _____ and that of K is expected to be ______. positive; less than 1 positive; greater than 1 negative; greater than 1 negative; less than 1 Provide Feedback
constant
The total energy of the universe is always_____
entropy
Thermodynamics relates spontaneity to a state function called________
use spontaneous redox rxt (ΔG < 0) to generate electricity * System does work on surroundings *Higher energy reactants----> lower energy products + electrical energy *Creating electricity is the desired outcome
Voltaic (aka galvanic) cells:
J/mol*K
What are the units for Entropy?
spontaneous in the reverse direction at all temperatures.
What can be said about an endothermic reaction with a negative entropy change?
spontaneous at low temperatures.
What can be said about an exothermic reaction with a negative entropy change?
combines system's entropy and enthalpy
What does Gibbs Free energy combine?
one reactant loses electrons, reducing agent is oxidized, oxidation number increases
What happens during oxidation?
Study of relationship between chemical change and electrical work Practical applications of thermodynamics
What is Electrochemistry?
96,485J/V mole (e-)
What is Faraday constant?
is one that occurs without ongoing outside intervention (such as performance of work by external force - you use a pulley to raise weight) *self-perpetuating at initial "spark" if any
What is a spontaneous process?
negative delta H; this means that a system released heat
What is an endothermic reaction related to (delta H)
positive delta H; this means that a system absorbed heat
What is an exothermic reaction related to (delta H)?
the study of energetics of chemical reactions
What is chemical thermodynamics?
recognized by the symbol (delta H) heat absorbed/lost during a chemical/physical change at constant P
What is enthalpy change?
is the thermodynamic state function that describes the amount of randomness (disorder) *A large value for entropy means a high degree of randomness. *An increase in entropy is a driving force for many changes.
What is the definition of entropy?
(delta)Gsystem = (delta)Hsystem-Temp*(delta)Ssystem
What is the equation for (delta) G system?
(delta) Ssys = q/T *q is heat transfered(H) *T is temperature
What is the equation for Ssystem?
n(S products) - n(S reactants) *where n = coefficients
What is the equation for Ssystem?
(delta)S universe = (delta)S system + (delta)S surrounding
What is the equation for entropy?
(delta)G = (delta)G degrees + RT lnQ *where Q is the reaction quotient (unitless) R is 8.314 J/molK (kJJ)
What is the equation for free energy?
E(universe)= E(system)+E(surroundings)
What is the equation for the first law of thermodynamics?
relationship between heat and energy and how it cannot be destroyed
What is the first law of thermodynamics?
states that processes occur spontaneously in the direction that increases entropy of universe
What is the second law of thermodynamics?
states that the entropy of a perfect crystal of a substance at absolute zero is equal to 0.
What is the third law of thermodynamics?
system is able to do more work
When (delta)G is large and negative_____
(delta) G is negative and spontaneous at all temperatures *slope is negative
When (delta)H is negative and (delta)S is positive?
(delta)G is positive and nonspontaneous at all temperatures *slope is positive
When (delta)H is positive and (delta)S is negative?
(delta) G can be negative or positive positive: spontaneous at higher temperatures negative: nonspontaneous at lower temperatures *slope is negative
When (delta)H is positive and (delta)S is positive?
greater than zero----> change occurs spontaneously less than zero----> reverse change occurs spontaneously equal to zero---->change is not spontaneous in either direction (the process is at equilibrium).
When (delta)S universe > 0 _________ When (delta)S universe < 0 _________ When (delta)S universe = 0 _________
spontaneous (negative) nonspontaneous (positive) at equillibrium * if spontaneous in one direction, not spontaneous in other
When G < 0______ When G > 0______ When G = 0______
E cell > E knot cell Ecell = E knot cell Ecell < E knot cell Ecell = zero5
When Q is less than 1, E cell____ When Q equals 1, E cell___ When Q is greater than 1_______ When Q equals K_____
(delta)G can be negative or positive positive: spontaneous at lower temperatures negative: nonspontaneous at higher temperatures *slope is positive
When is (delta)H is negative and (delta)S is negative?
increases decreases
When reactant concentration increase, potential_____ When product concentrations increase, potential_____
negative because the entropy has decreased
When the number of molecules in the product side is less than that of the molecules on the reactant side, S will be_____
Zinc metal can react with strong acids
Which metal will produce H2 gas when added to a solution containing a strong acid? View Available Hint(s) Which metal will produce gas when added to a solution containing a strong acid? Ag(s) Zn(s) Cu(s) Au(s)
• Liquid vaporising below its boiling point. • Liquid freezing above its freezing point liquid vaporizing above its boiling point. • Solid meting below its melting point • Gas condensing above its condensation point.
Which of the following is a nonspontaneous process? 1.Solid melting above its melting point. 2.Liquid freezing below its freezing point. 3.Gas condensing above its condensation point. 4.Liquid vaporising below its boiling point. 5.Solid meting below its melting point 6.Solid and liquid together at the melting point with no net freezing or melting. 7.Gas condensing below its condensation point 8.Liquid and gas together at the boiling point with no net condensation or vaporisation 9.Liquid freezing above its freezing point liquid vaporizing above its boiling point.
Solid melting above its melting point. Liquid freezing below its freezing point. Gas condensing below its condensation point. Liquid vaporising above its boiling point.
Which of the following is a spontaneous process? 1.Solid melting above its melting point. 2.Liquid freezing below its freezing point. 3.Gas condensing above its condensation point. 4.Liquid vaporising below its boiling point. 5.Solid meting below its melting point 6.Solid and liquid together at the melting point with no net freezing or melting. 7.Gas condensing below its condensation point 8.Liquid and gas together at the boiling point with no net condensation or vaporisation 9.Liquid freezing above its freezing point liquid vaporizing above its boiling point.
• Solid and liquid together at the melting point with no net freezing or melting. • Liquid and gas together at the boiling point with no net condensation or vaporisation.
Which of the following is at equilibrium? 1.Solid melting above its melting point. 2.Liquid freezing below its freezing point. 3.Gas condensing above its condensation point. 4.Liquid vaporising below its boiling point. 5.Solid meting below its melting point 6.Solid and liquid together at the melting point with no net freezing or melting. 7.Gas condensing below its condensation point 8.Liquid and gas together at the boiling point with no net condensation or vaporisation 9.Liquid freezing above its freezing point liquid vaporizing above its boiling point.
Decomposition of N2O4 gas to NO2 gas * N2O4(g) → 2NO2(g) involves an increase in entropy since there is only one mole of gaseous reactant vs. two moles of gaseous product.
Which process is expected to have an increase in entropy? A.)Formation of liquid water from hydrogen and oxygen gas. B.)Decomposition of N2O4 gas to NO2 gas C.)Iron rusting D.)Precipitation of BaSO4 from mixing solutions of BaCl2 and Na2SO4
b/c differ capacity for reaction
Why does a voltaic cell work spontaneously?
Chloromethane has a higher molar mass than hydrogen. Chloromethane experiences dipole-dipole interactions.
You just calculated that the heat of fusion for chloromethane is 6400 J/mol. The heat of fusion for hydrogen is 120 J/mol. What accounts for this difference?
arranges half-reactions in order of decreasing potential.
activity series :
nonspontaneous, make E cell negative
electrolitic =
sign of (delta)S at high Temp
sign of (delta)G is dominated by________at high temp
sign of (delta)H at low Temp
sign of (delta)G is dominated by_______at low temp
