Ch. 20 CHEM II, Ch 20 Part 1, Ch 20 Thermodynamics
Calculate the free energy change for the reaction Cu2O(s0--> Cu(s)+ 1/2O2(g) at 375k if deltaH=168 kJ/mol and deltaS=-9.63J/Kmol?
+172kJ/mol
Which of the following options correctly describe entropy? Select all that apply.
- Entropy is a measure of the energy dispersal of a system - The greater the freedom of motion of particles in a system, the greater the entropy of the system.
the entropy of the surroundings decreases in an ________ reaction
endothermic
Which of the following changes would result in an increase in the entropy of the system?
- A crystal of sodium chloride is heated from 275K to 290K -An ice cube melts at 273K - A tire is punctured, releasing the gas trapped inside
examples of spontaneous exothermic proccesses
-freezing and condensation at low temps -combustion reactions -oxidation of iron and other metals
what correctly describes entropy?
-the greater the freedom of motion of particles in a system, the greater the entropy of the system -entropy is a measure of the energy dispersal of the system
Which of the following is a correct description of the third law of thermodynamics?
The entropy of a perfect crystalline substance is 0 at 0 K.
The third law of thermodynamics states that a perfect of a pure solid substance has entropy at a temperature of 0 K.
crystal, zero
delta s universe =
delta s system + delta s surroundings, must be pos for a spontaneous proccess
The Gibbs ___ energy change (symbolized by thetha) is a measure of the spntaneity of a process and of the useful energy available from it.
free, G
In an endothermic reaction
heat is absorbed from the surroundings
The entropy of the surroundings decreases
in an endothermic reaction
if a given reversible reaction has posistive values for both delta H and delta S, the value of delta G will become ______ negative as temp increases, and the formation of the ______ will be increasingly favored
more, products
delta g is the amount of
useful work the system can do during a spontaneous reaction at constant temperature and pressure
Which of the conditions described below will result in a spontaneous reaction? Select all that apply. Multiple select question.
ΔSsys = 30 J/K; ΔSsurr = 10 J/K ΔSsys = -20 J/K; ΔSsurr = 25 J/K
under what conditions will the reaction of graphite shown below be spontaneous? C(s) + 2Cl2(g) -> CCl4(g); deltaH=-106.7kJ
- spontaneous only at low T
In the expression delta G = RTln(Q/K), delta G = 0 when Q is equal to K, ie when Q/K=
1
A process that can occur without a continuous input of energy is a(n) ___ process.
Spontaneous
A process that can occur without a continuous input of energy is a(n) _____ process. Multiple choice question.
Spontaneous
The entropy of the surroundings increases
in an exothermic reaction
As the temperature of a system increases, the entropy _____ due to a(n) _____ in the number of available energy states and thus a(n) _____ in the number of possible arrangements of molecules within those energy states. Multiple choice question.
increase, increase, increase
The dissolution of a molecular solute in a polar solvent (e.g, sugar dissolving in water) typically results in a(n)___ in entropy because both the molecules in the system and their energies are dispersed in a ___ volume.
increase; larger
what does the sign of Delta G indicate about whether the reactants or products are favored?
pos = reactant favored neg= product favored
Dissolving a solid or a liquid and entropy
the entropy of a dissolved solid or liquid is always greater than the entropy of the pure substance.
Which of the following options correctly describe entropy?
- Entropy is a measure of the energy dispersal of a system - The greater the freedom of motion of particles in a system, the greater the entropy of the system.
C(s) +O2(g) ---> CO2(g) N2(g) + O2(g) --> 2NO(g) pos/neg/=0 entropy?
=0 (1-1) = 0 (2-2) =0
according to the first law of thermodynamics what is delta E equal to?
q + w (heat plus work)
A particular process results in a decrease in the entropy of the system. If this process is spontaneous, what must be true about the entropy change of the surroundings?
ΔSsurr > -ΔSsys
Which of the following reactions are predicted to have a positive value for ΔSrxn? Select all that apply. Multiple select question.
H2CO3 (aq) → H2O (l) + CO2 (g) N2O4 (g) → 2NO2 (g)
A process that can occur only if the surroundings continuously supplies the system with an input of energy is called?
Nonspontaneous proccess
Spontaneous process
Occurs under specified conditions without a continuous input of energy
TEST Q: a reaction is proceeding toward equilibrium at a carttain stage the concentrations of reactants and products are such that delta G = delta G rxn. What conclusion can be reasonably drawn about the reaction at this time?
Q= 1
Select which phase change, melting or vaporization, will have a greater increase in entropy for a given substance. In addition, select the statement(s) that explain(s) why.
Vaporization of a substance The mobility of the particles increases much more when this phase change occurs.
Which of the following symbols denotes a standard free energy change?>
deltaG degree
The second law of thermodynamics states that the total _____ of the universe will _____ for any spontaneous process. Multiple choice question.
entropy, increase
Any spontaneous process is ________ because there is a net release of energy when it proceeds in that direction.
irreversible for example: a new car eventually rusts a spontaneous process, it cannot go back to being new
the different possible ways for arranging the particles of a system are called _________. The greater the number of microstates, the _______ the entropy of the system.
microstates, larger -each quantized state of the system is referred to as a microstate -at any instant, the total energy of the system is dispersed throughout one microstate, in the next instant it is dispersed throughout a different microstate
In an exothermic reaction, heat is _____ the surroundings. The particles of the surroundings have _____ freedom of motion and ΔSsurr therefore _____.
released to to; greater; increases
non spontaneous process
requires a continuous input of energy specified conditions
TEST Q: if the delta G > 0 and Q> K the reaction is proceeding in what direction
reverse direction
at a given set of conditions, each microstate has the _____ total energy as any other.
same -therefore each microstate is therefore equally likely -the number of microstates= the number of ways it can disperse its kinetic energy among the various motions of its particles
Select which phase change, melting or vaporization, will have a greater increase in entropy for a given substance? in addition, select the statements(s) that explain(s) why.
- the mobility of the particles increases much more when this phase change occurs - Vaporization of a substance
Which of the following statements correctly describe the general trends in standard entropy? Select all that apply.
-For two monatomic species, the one with the larger molar mass will have a higher standard entropy. -For elements with two allotropic forms, the one that is more mobile will have a greater value for standard entropy.
Which of the following conditions are specified by standard state conditions? Select all that apply.
-Solutions are at a concentration of 1 M. -Gases are at a pressure of 1 atm. -The standard state of an element is its most stable allotropic form at standard state temperature and pressure.
Which statements correctly describe the entropy changes that occur when an ionic solid dissolves in water? Select all that apply. Multiple select question.
-The hydration of highly charged ions generally results in a decrease in the entropy of the system. -The mobility of H2O molecules in such a solution is reduced since they are arranged in a specific way around the dissolved ions. -The dissociation of an ionic solute in water causes the entropy of the system to increase.
Match each type of chemical reaction with the energy and entropy changes it will cause in the surroundings. Instructions
-endothermic reaction: heat absorbed from surroundings -exothermic: heat is released to the surroundings -entropy of surrounding increases: exothermic -entropy of surrounding decreases: endothermic
Conditions specified as standard state conditions
-for thermodynamic calculations a reaction is carried out at 25 degrees celcius or 298 K (NOTE: not 0 degrees celcius or 273 like in gas law calc) -gases are at a pressure of 1 atm -solutions are at a concentration of 1M -the standard state of an element is its most stable allotropic form at standard state temperature and pressure
Match each state of matter with the appropriate characteristics at standard state.
-gases: pressure of 1 atm -solutions: 1 M concentration -solids or liquids: pure substance in its most stable form
do spontaneity (spontaneous or nonspontaneous) of a reaction and the sign of delta H have a correlation
-it is possible for an exothermic process to be non spontaneous -an endothermic process may be spontaneous under one set of conditions, but non spontaneous at a different temperature and pressure
examples of spontaneous endothermic proccesses
-melting and vaporization at higher temps -ice will spontaneously melt above 0 degrees celcius -dissolution of sodium chloride in water -dissolving of most soluble salts -crystalline solid + liquid = ions in solution -crystalline solid = gases + ions in solution
what factors increasing entropy?
-raising the temperature -phase changes from solid, liquid, to gas -entropy larger for a large monoatomic substance vs. a small one (larger for larger molecules) -allotropes with more atoms vs. fewer -a more complex substance vs. a more simple substance in the same phase, if their molar masses are similar -more moles= more entropy
The standard free energy change for a reaction is the free energy change for the reaction under standard state conditions which are
1 atm of pressure and concentration of 1 M
If we know that the entropy change for a reaction is x J/K and the system absorbed y kJ of heat during that reaction, what is the temperature at which this occurred (in K)?
1000y / x
If we know that the enetropy chnage for a reaction is x J/K and the system absorbed y KJ of heat during that reaction, what is the temperature at which this occured in K?
1000y/x
TEST Q: which of the following is true 1) the standard molar entropy of a pure compound increases with increasing temperature 2) the standard molar entropy for elements in their elemental forms at standard state is zero
2 is WRONG
TEST Q: A certain proccess has delta H > 0, delta S < 0, and delta G < 0. The values of delta H and delta S do not depend on temperature. which of the following is a correct conclusion about this proccess? A)It is spontaneous at low T B) It is nonspontaneous at all T C) None of these choices are correct D) It is spontaneous at high T E) It is spontaneous at alllT
B) It is non spontaneous at all T +G = +H-(-S) no matter what t you put, you get, two negatives make a pos, and since g will pos, the reaction will be non spontaneous
TEST Q: is the following proccess spontaneous? picture of a solid going to a gas A) No because - H B) Yes because +H C) Yes because +S D) No because -S e) it is impossible to know without knowing the temperature of the system
E) the calculation of delta G is how we tell whether a reaction is spontaneous or not, the sign of delta S or H on its own cannot tell us the spontaneity of the system
Which of the following correctly describes the first law of thermodynamics?
Energy can be converted from one form to another, but it cannot be created or destroyed.
Which of the following options correctly reflect the relationships between ΔSsurr, ΔHsys, and T (at constant pressure so qsys = ΔHsys)? Select all that apply. Multiple select question.
If ΔHsys is negative, ΔSsurr will be positive. ΔSsurr is inversely proportional to temperature.
The combustion of glucose, represented by the equation C6H12O6 (s) + 6O2 (g) → 6CO2 (g) + 6H2O (g), is an exothermic reaction. Does this reaction cause an increase or decrease in entropy for the system and its surroundings? Multiple select question. Increase in ΔSsurr
Increase in ΔSsurr Increase in ΔSsys
Since entropy is typically tabulated in units of __/K and standard enthalpies are typically tabulated in units of ___/mol, it is usually necessary to perform a unit conversion when calculating Gibbs free energy.
J; kJ
What effect does increasing the temperature of a gas have on its entropy, and why? Select all that apply
The entropy of a system increases as the temperature increases. As the temperature of a system is increased, all types of kinetic energies increase.
The formation of water from its elements is exothermic (ΔHsys = -572 kJ/mol) and spontaneous although the reaction results in a large decrease in the entropy of the system: 2H2(g) + O2(g) → 2H2O(ℓ) ΔSsys = -327 J/K Which of the following is the best explanation how this process is able to obey the second law of thermodynamics that all spontaneous processes increase the entropy of the universe?
The reaction is highly exothermic and the surroundings increase in entropy.
Physical States and Changes of State and entropy
as the freedom of motion of the substance increases, the entropy increases. The size of the entropy change is such that ΔS°vap is much greater than ΔS°fus .
the third law of thermodynamics states that a perfect _______ of a pure solid substance has _______ entropy at temperature of 0 K or at absolute zero.
crystal, zero
TEST Q: identify the compound with the standard free energy of formation equal to zero KBr(s), NO(g), O3(g), H2(g), it is hard to determine
d) H2
Which of the following values must be known in order to calculate the change in Gibbs free energy using the Gibbs equation?
delta G sys = delta H sys - T(delta S sys)
TEST Q: given thermodynamic data like delta g, delta h, delta s. how do you find boiling point?
delta H(j) / delta S(j)
what are the two things that make up delta S universe and what does it have to be to be spontaneous
delta S surroundings + delta S system Must be positive (delta S universe > 0)
for any reaction qsys ____ -qsurr. the heat transderred is specific for the reaction and is the same regardless of the temp of the surroundings.
delta S surroundings = - delta S system
A particular process results in a decrease in the entropy of the system. If the process is spontaneous, what must be true about the entropy change of the surroundings?
delta S surroundings > - delta S system
If "q" joules of heat are released reversibly when a substance is at a temperature T, what equation represents the change in entropy, delta S system during this process?
delta S sys = - q/T
TEST Q: Which of the following is true for a system at equilibrium?
delta S system = -delta S surroundings not: delta s system = delta s surr = 0 delta s universe is > 0 (it should be equal to 0) delta s universe = delta s system
TEST Q: to calculate delta G for any condition (standard or non standard)
delta g = delta g rxn + RTln(Q) dont forget to convert kj to j
TEST Q: finding equilibirum constant when given delta g reaction
delta g reaction = -RTlnQ Because R is in joules the anwser will be in joules so you have to convert back to kj
TEST Q: which one is always pos for a spontaneous procces? delta s system, surroundings, universe, delta s universe or surroundings
delta s universe
he first law of thermodynamics states that _____ is always conserved.
energy
the ______ of a system, symbolized by the letter S, is related to the number of possible ways that energy of a system can be dispersed.
entropy (the greater the freedom of motion of particles in a sustem, the greater the entropy of the system)
The second law of thermodynamics states that the total ___ of the universe will ___ for any spontaneous process.
entropy; increase
The first law of thermodynamics states only that the total energy change of the universe is __. However, the first law of thermodynamics __ account for the direction of spontaneous change.
equal to zero; cannot
Since entropy is a state function, the total entropy change for a process is given by S _____ - S _____.
final , initial
A key factor that influences reaction spontaneity is changes in the of motion of the particles in the system, i.e. the of the energy of motion of the particles.
freedom, dispersal
The two key factors that influence reaction spontaneity are changes in the ___ of motion of the particles in the system and ___ of the energy of motion of the particles.
freedom, dispersal
H2O (l) ----> H2O (s) delta S sys = -22 J/K why does this process obey the second law of thermodynamics?
freezing is exothermic, the surroundings increase in entropy (the addition of heat causes a much greater increase in entropy when the temp is low (S=q/t) this is why water freezes only at low temperatures
Without doing a calculation predict the sign of delta S for the following reactions: (a) H2S(g) + 1/2 O2(g) ---> 1/8 S8 (s) + H2O(g) (b) HCl(aq) +NaOH(aq) ---> NaCl(aq) + H2O(l) (c) 2NO2(g) ---> N2O4(g)
from a solid liquid to gas randomness increases -look for number of moles of gas' decreasing aq counts too (products - reactants) (a) neg (1-1.5) = neg (b) neg (1 aq- 2 aq) = neg (c) neg (1-2) neg
each state of matter and its most appropriate standard state Gases Solutions Solids or Liquids for standard molar entropies, and in what unit
gases = pressure of 1 atm solutions= 1 M concentration Solids and liquids = Pure substance in its most stable form usally at 298K J/mol.K
The dissolution of a molecular solute in a polar solvent (e.g., sugar dissolving in water) typically results in a(n) _____ in entropy because both the molecules in the system and their energies are dispersed in a _____ volume.
increase, larger
TEST Q: Give the name of the reaction that does not achieve the theoretical limits with respect to free energy in thermodynamics?
irreversible reaction
TEST Q: a certain proccess has delta S univ > 0 at 25 degrees celicus, what does one know about the proccess?
it is spontaneous at 25 degrees celcius
TEST Q: Which of the following statements is true about the equilibirum constant for a reaction if delta G is negative? k=0, k=1, k>1, k<1, k< 10^-10
k>1 -RTln(K)
When Q < K Q > K Q = K What is the sign for delta G
less than zero more than zero equal to zero
in an exothermic reaction heat is
lost to the surroundings
few microstates (smaller W) = higher or lower entropy? more microstates (larger W) has higher or lower entropy?
lower higher
The different possible ways for arranging the particles of a system are called _____. The greater the number of these states, the _____ the entropy of the system
microstates, larger
Does a spontaneous process mean fast or slow?
no, it means that in a given time, the process will occur on its own -ex: graphite is more stable than diamond, so the conversion of diamond into graphite is spontaneous. however its so slow that it will not occur in your lifetime or many generations afterwards
Finding delta S for a reaction
products - reactants (despite whether they are solid liquid or gas) always multiply the entropy of each product and or reactant by its stoichiometric coefficients
The __ molar entropy has the symbol S and is defined as the entropy of 1 mole of the substance at a pressure of ___ atm.
standard, 1
Entropy is a _______ function and the change in entropy for a process therefore depends only on the ________ between the final and initial rates, not on the path taken for the process.
state, difference
Gibbs free energy change definition
symbolized by delta G -is a measure of the spontaneity of a process, and of the useful energy available from it
the reaction that results in an overall increase in the number of gas molecules has a pos sign for delta S rxn. Why?
the entropy of a substance in the gas phase is much higher than its entropy in the liquid or solid phase
Atomic size and entropy
the entropy of atoms generally increases down a group since the number of microstates increases. ex: HBr(g) > HCl(g) Ba(s) > Ca(s) > Mg(s)
Molecular complexity and entropy
the entropy of molecules increases as they become more complex and the number of atoms increases. ex: N2O4(g) > NO2(g) ex 2: S2F10 > SF6 > SF4 ex 3: CH3CH2OH(l) CH3OCH3(l) both have the same number of bonds but the first one forms a hydrogen bond and the other does not, hydrogen bond the freedom f motion is seized that is why the second one is greater than the first CH3CH2OH(l) < CH3OCH3(l)
TEST Q:If delta G rxn < 0 and Q < K the reaction is proceeding in what direction
the reaction is proceeding in the foward direction to reach equilibirum
Find the formation of 1 mole of PCl5 (g) from its elements
the reaction is: 1/4 P(s) + 5/2 Cl2(g) ---> PCl5 (g) delta S (reaction) = [353]- [(1/4)(41.1) + (5/2)(223)] = -214.775
Endothermic changes
the system gains heat from the surroundings. This heat lost by the surroundings decreases the freedom of motion of the particles which decreases the entropy of the suroundings. Therefore qsys > 0, qsurr < 0, and ΔSsurr < 0.
Exothermic changes
the system loses heat to the surroundings. The heat gained by the surroundings increases the freedom of motion of the particles which increases the entropy of the suroundings. Therefore qsys < 0, qsurr > 0, and ΔSsurr > 0.
The second law of thermodynamics states that
the total entropy of the universe will increase for any spontaneous process, all real proccesses occur spontaneously in the direction that increases the entropy of the univserse
when Q and K are very similar, the reaction releases or absorbs
very little energy
At a certain temperature, the change in entropy of the system is calculated to be ΔSsys. If the system is at equilibrium, what is the value of ΔSsurr under these conditions?
ΔSsurr = -ΔSsys
predict the sign of delta S for each proccess below (a) O2(g) (1.0 L at 1 atm) --> 02(g) (0.10L at 10atm) (b) Cu(s) (350C and 2.5 atm) ---> Cu(s) (450C and 2.5 atm) (c) Cl2(g) (100C and 1 atm) ---> Cl2(g) (10C and 1 atm)
(a) neg (b) pos (c) neg
Calculate the standard entropy change for the following reaction at 25oC. Use the values provided in the table below. 2CO (g) + O2 (g) → 2CO2 (g)
-173.6 J/mol⋅K
Examples of spontaneous proccesses
-a spark to ignite gasoline -a push to knock a book off a desk -roll a ball down a slope -a match continues to burn after being lit -a soluble salt dissolves when it is mixed with water -iron rusts when exposed to salty air -a satellite falls to earth -average car prices increase
examples of factors that increase the likelihood of a reaction will be spontaneous
-energy is released in the form of heat -a gas is generated from a liquid -a liquid is generated from a solid
Solutions
1 M concentration
Which of the following factors increase the likelihood that a reaction will be spontaneous? Select all that apply.
A gas is generated from a liquid. Energy is released in the form of heat. A liquid is generated from a solid.
The first law of thermodynamics states that __ is always conserved
Energy
TEST Q: if K< 1 is the reaction spontaneous or non spontaneous, what about K > 1
K < 1 = nonspontaneous ex: -8.314(298)ln(.45) = pos delta g K > 1 = spontaneous ex: -8.314(298)ln(2) = neg delta g
Given the balanced chemical equation CH4 (g) + 2O2 (g) → CO2 (g) + 2H2O (g), which of the following equations should be used to calculate the total entropy change for this reaction? (States of matter have been omitted for simplification.) Multiple choice question.
S[CO2] + 2(S[H2O]) - S[CH4] - 2(S[O2])
in an endothermic reaction heat is
absorbed from surroundings
In an endothermic proccess, the surroudnings provides the heat ______ by the system, and S surr ______.
absorbed, decreases qsys >0 qsurr <0 and delta s surr <0
In an exothermic prooccess, the surroundings ____ the heat released by the system and S surroundings _______.
absorbs, increase qsys < 0 qsurr >0 and delta s surr >0
the standard state of an element is its most stable _____ form at standard temperature and pressure.
allotropic
When Q and K are very different, the reaction releases or absorbs
alot of energy
A particular process results in a decrease in the entropy of the system. If this process is spontaneous, what must be true about the entropy change of the surroundings?
deltaSsurr > -deltaSsys
TEST Q: the thermodynamic qyanity that expresses the extent of randomness or disorder is
entropy
for a system at equilibrium delta G ______ 0
equal
The dissolution of a molecular solute in a polar solvent typically results in a ______ in entropy because both the molecules in the system and their energies are dispersed in a ________ volume.
increase, larger
As W increases entropy _____
increases
the larger the equilibrium constant K the more _____ the value of delta g reaction and the more the _____ are favored at equilibrium.
negative, products
2C(s) + O2(g) --> 2CO(g) pos/neg/=0 entropy?
pos (2-1) = 1
For a chemical reaction, ∆S°rxn = ΣnS°....
products, reactants
Entropy is a ___ function and the change in entropy for a process therefore depends only on the ___ between the final and initial states, not on the path taken for the process.
state, difference
Entropy is a function, and the change in entropy for a process therefore depends only on the between the final and initial states, not on the path taken for the process.
state, difference
For a chemical reaction delta S is equal to the
sum entropy of products - sum entropy of reactants
In which cases do the substances(s) on the left have a higher entropy than the substance(s) on the right?
- 2NO2(g) vs. N2O4(g) -C3H8(g)vs. C2H6(g)
Match each symbol in the equation S = k ln W correctly with its meaning.
-S: entropy -k: constant -ln: natural logarithm -W: number of microstates
In the expression deltaG=RT Ln(Q/K), deltaG=__ when Q is equal to K, i.e., when Q/K= ___.
0,1
for a nonspontaneous proccess delta G _____ 0
greater than
for a spontaneous proccess delta G ______ 0
less than
In all spontaneous endothermic proccesses exhibit an increase in entropy
true
Calculate the entropy change of the surroundings in J/mol⋅K when 30 kJ of heat is released by the system at 27oC.
+100
definition of thermodynamics
branch of physics concerned with heat and temp and their relation to energy and work
as temperature increases delta S surroundings _______.
decreases
Gases
pressure of 1 atm
Calculate ΔSuniv and identify the process CO2 (g) → CO2 (aq) as spontaneous, nonspontaneous, or at equilibrium at 25oC. Use the values provided in the table below.
ΔSuniv = -27.2 J/mol⋅K The reaction is nonspontaneous at this temperature.
What effect does increasing the temperature of a gas have on its entropy, and why?
- The entropy of a system increases as temperature increases -as the temperature of a system is increases, all types of kinetic energies increase
Calculate the standard entropy change for the reaction 2A + 3B → 2C.
-8
the effect on entropy of increasing the temperature of a gas
-as temperature of a system is increased, all kinetic energies increase, along with entropy
A system is in a state of when ΔSuniv = 0.
equilibrium
without doing calculate predict sign of delta S (a) Ag+ (aq) + Cl- (aq) ---> AgCl (s) (b) KBr(s) ---> KBr(aq) (c)CH3=CH2(g) ---> H2C-H2C-CH2(g)
(a) neg (0-2) = -2 (b) pos (1-0) =1 (c) becomes less complex loses entropy neg (chains are less complex)
delta s surroundings = ? wha tis delta s surroundings equal to for a process at constant P?
-qsys / T -delta h sys/ T
3H2(g) + n2(g) ---> 2NH3(g) N2(g) + 2O2(g) --> N2O4(g) 2H2(g) + O2(g) ---> 2H2O(g) all of these reactions have neg/pos/=0 entropy?
neg (2-3) = -1 (1-3) = -2 (2-3) = -1
predict the sign of delta S sys for each of the following proccesses (a) Gasoline vapors mix with air in a car engine. (b) Hot air expands. (c) Humidity condenses in cold air. (d) A pond freezes in the winter. (e) Atmospheric Co2 dissolves in the ocean. (f) An apple tree bears fruit.
(a) pos (b) pos (c) neg (d) neg (e) neg (f) neg
Calculate the entropy change of the surroundings in J/mol when 30 kJ of heat is released from the system at 27 degrees celcius
+100 this is the result of -(30,000 J/300 K)
Which statements correctly describe the entropy changes that occur when an ionic solid dissolves in water?
- The dissociation of an ionic solute in water causes the entropy of the system to increase - The mobility of H2O molecules in such a solution is reduced since they are arranged in a specific way around the dissolved ions - The hydration of highly charged ions generally results in a decrease in the entropy of the system
Which of the following statements correctly explain in the increase in entropy that occurs when a substance changes from a solid to liquid, or liquid to gas?
- The energy of the particles increases during theses phase changes. -The freedom of movement of the particles increases in the change solid --> liquid --> gas
Consider the chemical reaction 2SO3(g) --> O2(g)+2SO2(g), for which deltaH= +198.4kJ and deltaS=+187.9J/K. Which of the following statements correctly describe the effect of temperature on the spontaneity of this reaction?
- The reaction is spontaneous only at higher temperartures - The reaction will become more spontaneous as the temperature increases
The third law of thermodynamics states that a perfect ___ of a pure solid substance has ___ entropy at a temperature of 0 K.
- crystal - zero
the relationship between delta S surroundings / delta H system and T (at constant pressure so that q system = delta H system)
- delta H / T = delta S surroundings furthermore: -if delta h is negative, delta s will be pos -delta s surroundings is directly proportional to temperature
A reaction is found to be spontaneous only at high temperatures. Which of the following must be true?
- deltaSrxn > 0 -deltaHrxn>0
Which of the following options correctly reflect the relationships between deltaSsurr, deltaHsys, and T(at constant pressure so qsys=deltaHsys)?
- if deltaHsys is negative, deltaSsurr will be positive -deltaSsur is inversely proportional to temperature
The combustion of glucose, represented by the equation C6H12O6(s)+6CO2(g) --> 6CO2(g)+6H2O(g) is an exothermic reaction. Does this reaction cause an increase or decrease in entropy for the system and surrounding?
- increase in Ssurr - Increase in Ssys
A reaction taking place at 100°C has an entropy change of 200J/K and an enthalpy change of -20kJ. Which of the following expressions would be used to calculate deltaG under these conditions?
-20,000-(373)(200)
In which of the following options does the first species of each pair have a greater standard entropy? Select all that apply. Multiple select question.
-A more complex substance vs. a simpler substance in the same phase if their molar masses are similar -A gas at 250°C vs. the same gas at 100°C
Which of the following statements correctly reflect the relationship between the spontaneity of a reaction and the sign of ΔH? Select all that apply.
-An endothermic process may be spontaneous under one set of conditions but nonspontaneous at a different temperature and pressure. -It is possible for an exothermic process to be nonspontaneous.
Rank the following compounds in order of decreasing standard molar entropies. Place the compound with the highest entropy at the top of the list. Instructions
-C3H8 -CH4 (g) -CH4 (l)
Which of the following statements correctly explain the increase in entropy that occurs when a substance changes from a solid to a liquid, or from a liquid to a gas? Select all that apply
-The energy of the particles increases during these phase changes. -The freedom of movement of the particles increases in the change solid → liquid → gas.
examples of changes that would result in an increase in entropy
-an icecube melts at 273K (solid to liquid) -a crystal of sodium chloride is heated from 275K to 290K (increasing temperature) -a tire is punctured releasing the gas trapped inside or opening a stopcock with a gas trapped inside (increasing the volume increases the number of translational energy levels the particles can occupy as they move from one location to another) -mixing a pure solid and pure liquid to form a solution
two key factors that influence reaction spontaneity
-freedom of motion of the particles in the system -dispersal of energy of motion of particles
A reaction is known to have deltaH equal to -5kJ and deltaS equal to -100J/K. What is the temperature (in K) at which is the reaction becomes spontaneous?
50K
What is a spontaneous process?
A process that occurs under specified conditions without a continuous input of energy
Which of the following statements correctly describe the general trends in standard entropy? Select all that apply
For elements with two allotropic forms, the one that is more mobile will have a greater value for standard entropy. For two monatomic species, the one with the larger molar mass will have a higher standard entropy.
H2O (l) → H2O (s); ΔSsys = -22 J/K The process shown above is spontaneous at temperatures below 0oC, even though the entropy of the system is decreasing. Which of the following is the best explanation for the way in which this process obeys the second law of thermodynamics? Multiple choice question.
Freezing is exothermic; the surroundings increase in entropy.
Which of the following options correctly reflect the relationships between ΔSsurr, ΔHsys, and T (at constant pressure so qsys = ΔHsys)? Select all that apply.
If ΔHsys is negative, ΔSsurr will be positive. ΔSsurr is inversely proportional to temperature.
When a reaction is at equilibrium, the reaction quotient Q is always equal to ___ and deltaG is equal to ___.
K, 0
reactions predicted to have a positive value for delta S
N2O4 (g) ----> 2NO2 (g) (In the decomposition of N2O4, the product molecules are less complex, but the moles of gas have increased) H2CO3 (aq) -----> H2O (l) + CO2(g) (in the decomposition of carbonic acid, the number of gas moles increases, there fore the total entropy of the system increases)
Solids or liquids
Pure substance in its most stable form
Select the definition of entropy in terms of the number of microstates over which the energy of a system can be dispersed. Multiple choice question.
S = k ln W
what do all the symbols in S = k ln W mean?
S= entropy k=Boltzman constant 1.38 x 10^-23 J/K ln= natural log W= number of microstates
Two unknown reactions (A and B) are analyzed. It is found that reaction A is exothermic, while reaction B is endothermic. Which of these reactions is spontaneous?
Spontaneity can not be determined from the information given
Two unknown reactions (A and B) are analyzed. It is found that reaction A is exothermic, while reaction B is endothermic. Which of these reactions is spontaneous?
Spontaneity cannot be determined from the given information.
A process that can occur without a continuous input of energy is a called a?
Spontaneous process -all chemical processes require energy (activation energy) to take lace, but once a spontaneous process has begun no further input of energy is needed
Which of the following is an application of the second law of thermodynamics?
a gas expands because matter tends to spread out
calculating K given delta G?
delta G = -(8.314)(298K)(lnK)
enthalpy vs entropy symbol
delta H vs. Delta S
the first law of thermodynamics states that _____ is always conserved.
energy, it is neither created nor destroyed, but is transferred in the form of heat and or work -it is always constant, so the energy of the universe is zero
The ___ of a system, symbolized by the letter S, is related to the number of different possible ways the energy of a system can be dispersed.
entropy
The of a system, symbolized by the letter S, is related to the number of different possible ways the energy of a system can be dispersed.
entropy
the entropy of the surroundings increases in a _______ reaction
exothermic
temperature changes and entropy
for a given substance, S° increases as the temperature increases.
In an exothermic reaction
heat is lost to the surroundings
if a given process proceeds spontaneously toward the products, the value of the reaction quotient Q is ___ the equilibirum constant K, and thetaG for the reaction will be ___.
less than; negative
How is the number of microstates in a system, W, related to the entropy of the system, S?
ln W = S
An atom of hydroden is bonded to a metal surface (but free to move accross it) with 10 possible microsites of attachment. What would be the effect of increasing the size of the metal surface to 20 possible sites?
ln(20)/ln(10) = 1.3 the entropy would increase, but it would be less than double the original entropy
If a reaction is spontaneous is one direction, is it spontaneous in the reverse direction under the same conditions?
no it is not -it would be non spontaneous in the reverse direction
a chemical reaction that is procceeding toward equilibirum is _______ in that direction.
spontaneous
water freezes at -20 degrees and delta s system <0, spontaneous or no? what about the condensing of water?
spontaneous also spontaneous
The standard free energy change for a reaction is the free energy change for the reaction under ___ state conditions, which assumes that all gases are at ___ atm of pressure and all solutions have a concentration of ___ M.
standard, 1, 1
TEST Q: with thermodynamics one cannot determine?
the speed (or rate of reaction)
find delta g for a reaction given delta H final and S values
use delta G = delta H- Tdelta S assume T= 298 K
Dissolving a gas and entropy
when a gas dissolves in a liquid, the entropy always decreases but when dissolved in another gas it increases.
the first law of thermodynamics states only that the total energy of the universe is _____. However, ______ account for the direction of spontaneous change.
zero, cannot
When heat is transferred from the system to the surroundings, the amount of energy that is dispersed is greater when the temperature is low. Which of the following reflect this relationship (at constant pressure)?
ΔSsurr = - ΔHsys/T ΔSsurr = - qsys/T
