Exam 2

What are the three ways we are able to predict the sign of the entropy change by examining the system on a molecular level, an increase in the entropy of a system. if there is n increase in... ?

(a) in volume (or a decrease in pressure; this increases the number of locations of the particles in space), (b) temperature (this increases the total energy of the system) (c) the number of independently moving particles (this increases the number of ways both energy and position can be distributed in the system).

Consider the reaction between nitrogen and hydrogen to yield ammonia. The equilibrium concentrations of NH3, N2, and H2 were determined at 472°C to be [H2] = 0.1207 M, [N2] = 0.0402 M, [NH3] = 0.00272 M. What is the value of Kc? (HINT: Look at the solved problem in the margin!) N2(g) + 3 H2(g) ⇌ 2 NH3(g)

0.105

the activity of a solvent in dilute solution is ________

1

Standard state is the most stable form of pure solids. liquid, or gas at P=________ and __________K

1 atm, 298K

At 800 ºC, Keq = 0.0100 for the following reaction: 2SO2(g) + O2(g) ⇄ 2SO3(g) What is the numerical value for the equilibrium constant for this reaction: 4SO3(g) ⇄ 4SO2(g) + 2O2(g)

10000

Consider a reaction in which 1.00 mole of SO2 (g) and 1.00 mole of O2 (g) are added to a 1.00 L container at 1000 K and allowed to react until equilibrium is achieved. At equilibrium, the container has 0.919 moles of SO3 (g). What is the value of Kc?

238

The number of vibrational modes (different types of vibrations) in a molecule is ___________ for linear molecules

3N-5 (N= number of atoms)

The number of vibrational modes (different types of vibrations) in a molecule is for nonlinear molecules

3N-6

A mixture of 1.374 g of H2 and 70.31 g of Br2 is heated in a 2.00-L flask at 700 K. The following equilibrium is established: H2(g) + Br2(g) ⇄ 2HBr(g) At equilibrium the vessel is found to contain 0.566 g of H2.What is Kp for this reaction?

58.2

What is the value of Kc for the following reaction at 400 K? (Find the simulator...) N2 (g) + 3 H2 (g) ⇌ 2 NH3 (g) A) 5.06×104 B) 1.0 C) 0.0219 D) 4.03 E) 3.43

A) 5.06×104

2Ag(s) + Zn2+(aq) ⇄ 2Ag+(aq) + Zn(s) Which is the correct equilibrium constant for the reaction above? A) K = [Ag+]2/[Zn2+] B) K = 2[Ag+]/[Zn2+] C) K = [Ag+]/2[Zn2+] D) K = [Zn2+]/[Ag+]2 E) K = [Ag+]2/[Zn2+]2

A) K = [Ag+]2/[Zn2+]

What is the equilibrium constant expression for the following reaction? CH3COOH(aq) → H+(aq) + CH3COO−(aq) A) Keq =[H+][CH3COO−]/[CH3COOH] B) Keq[CH3COOH] = Kp[H+][CH3COO−] C) Keq =[H+]2[CH3COO−]/[CH3COOH] D) Keq =[CH3COOH]/[H+][CH3COO−] E) Keq =[H+][CH3COO−]

A) Keq =[H+][CH3COO−]/[CH3COOH]

What is the equilibrium constant expression for the following reaction? H2(g) + I2(g) ⇌ 2 HI(g) A) Kp = P2HI/PH2PI2 B) Kp = PHI/PH2PI2 C) Kp = [HI]2/[H2][I2] D) Kp = P2HI/P2H2P2I2 E) Kp = PH2PI2/P2HI

A) Kp = P2HI/PH2PI2

What is equilibrium? A) The point at which there is no net change in the amounts of reactants and products over time. B) The point at which all of the limiting reactant has been used up. C) The point at which a reaction stops taking place. D) The point at which the moles of reactants equals the moles of products. E) The point when the reverse reaction has become faster than the forward reaction.

A) The point at which there is no net change in the amounts of reactants and products over time.

If Q < Keq, what does that say about the relationship of the system to equilibrium? A) The system is not at equilibrium and will produce more products to reach equilibrium (shift to the right). B) The system is at equilibrium. C) There is no relationship between Q and Keq. D) The system will produce both more reactants and more products to reach equilibrium. E) The system is not at equilibrium and will produce more reactants to reach equilibrium (shift to the left).

A) The system is not at equilibrium and will produce more products to reach equilibrium (shift to the right).

In an exothermic equilibrium reaction, increasing the reaction temperature favors the formation of reactants. A) True B) False

A) True

The number obtained by substituting starting reactant and product concentrations into an equilibrium-constant expression is known as the reaction quotient. A) True B) False

A) True

True or False: Adding more product to a system at equilibrium causes a shift toward the reactants. A) True B) False

A) True

At a certain temperature, 0.300 moles of NO, 0.200 moles of Cl2, and 0.500 moles of ClNO were placed in a 25.0 L vessel and allowed to reach equilibrium: 2 NO(g) + Cl2(g) ⇄ 2 ClNO(g). At equilibrium, 0.600 moles of ClNO were present. The number of moles of Cl2 present at equilibrium is A) 0.100 mol B) 0.150 mol C) 0.200 mol D) 0.250 mol E) 0.300 mol

B) 0.150 mol

Which of the following statements is true? 1. The equilibrium-constant expression depends on the stoichiometry of the reaction. 2. The value of the equilibrium constant varies with temperature. 3. The value of the equilibrium constant depends on the initial amounts of the reactants and products. A) 2 and 3 B) 1 and 2 C) 2 only D) 1 only E) 3 only

B) 1 and 2

The effect of a catalyst on a chemical reaction is to react with product, effectively removing it and shifting the equilibrium to the right. A) True B) False

B) False

True or False: Conducting an endothermic reaction at a lower temperature will produce more products. A) True B) False

B) False

Which of the following represents the equilibrium constant for the following general reaction? j A + k B ⇌ p R + q S (Lowercase letters represent stoichiometric coefficients, while uppercase letters represent chemical compounds.) A) Kc = ([p R][q S])/([j A][k B]) B) Kc = ([R]p[S]q)/([A]j[B]k) C) Kc =([A]j[B]k)/([R]p[S]q) D) Kc = (pq)/(jk) E) Kc = P(R)pP(S)q/P(A)jP(B)k F) Kc = [R][S]/[A][B]

B) Kc = ([R]p[S]q)/([A]j[B]k)

Given the following reaction and equilibrium constant, which statement is false? HF (aq) ⇄ H+ (aq) + F- (aq) Kc = 6.8 × 10-4 A) At equilibrium, there is more HF in solution than its ion. B) The reaction only proceeds in one direction, toward HF. C) For the reverse reaction Kc = 1.5 × 103. D) [H+] = [F-] even if Q > Kc E) Kc = [H+][F-]/[HF]

B) The reaction only proceeds in one direction, toward HF.

At equilibrium, __________. A) all chemical reactions have ceased B) the rates of the forward and reverse reactions are equal C) the rate constants of the forward and reverse reactions are equal D) the limiting reagent has been consumed E) the value of the equilibrium constant is 1

B) the rates of the forward and reverse reactions are equal

What will increase the production of ammonia from nitrogen gas and hydrogen gas? (CHOOSE ALL CORRECT ANSWERS; THERE MAY BE MORE THAN ONE CORRECT ANSWER.) N2(g) + 3 H2(g) ⇌ 2 NH3(g) ΔHrxn = −92.4 kJ/mol A) Increase the volume of the system. B) Add hydrogen gas to the system. C) Add nitrogen gas to the system. D) Add ammonia gas to the system. E) Remove gaseous ammonia from the system and recycle the reactants. F) Cool the reaction down. G) Add helium gas to the system.

B,C,E,F

In the diatomic nonmetals, which are liquids?

Br2

The value of Keq for this reaction is 0.25: SO2 (g) + NO2 (g) ⇄ SO3 (g) + NO (g) What is the value of Keq at the same temperature for the reaction below? 2 SO2 (g) + 2 NO2 (g) ⇄ 2 SO3 (g) + 2 NO (g) A) 0.25 B) 0.12 C) 0.062 D) 0.50 E) 16

C) 0.062

Consider the following reaction at equilibrium. 2CO2 (g) ⇄ 2CO (g) + O2 (g) ΔH° = −514 kJ Le Chatelier's principle predicts that the equilibrium partial pressure of CO(g) can be maximized by carrying out the reaction __________. A) at high temperature and high pressure B) at high temperature and low pressure C) at low temperature and low pressure D) at low temperature and high pressure E) in the presence of solid carbon

C) at low temperature and low pressure

The equilibrium constant for the gas phase reaction 2NH3(g) ⇄ N2(g) + 3H2(g) is Keq = 230 at 300 °C. At equilibrium, __________. A) only reactants are present B) reactants predominate C) products predominate D) only products are present E) roughly equal amounts of products and reactants are present

C) products predominate

Which of the following sets of conditions causes the Haber process simulator reaction vessel to explode? A) 5.0 mol N2 3.0 mol H2 5.0 mol NH3 600 K 1.0 L catalyst Ru B) 1.0 mol N2 3.0 mol H2 10.0 mol NH3 600 K 1.0 L catalyst Fe C) 1.0 mol N2 3.0 mol H2 0.0 mol NH3 600 K 1.0 L catalyst Fe D) 10.0 mol N2 3.0 mol H2 10.0 mol NH3 600 K 1.0 L catalyst Ni E) 1.0 mol N2 3.0 mol H2 10.0 mol NH3 600 K 1.0 L catalyst Ni

D) 10.0 mol N2 3.0 mol H2 10.0 mol NH3 600 K 1.0 L catalyst Ni

Kc for the reaction below equals 125 at a particular temperature. F2(g) + Cl2(g) ⇄ 2 FCl(g) What is the value of Kc for the reaction given below? 1/2 F2(g) + 1/2 Cl2(g) ⇄ FCl(g) A) Kc = 62.5 B) Kc = 0.0160 C) Kc = 125 D) Kc = 11.2 E) Kc = 0.0894

D) Kc = 11.2

1.0 mole of SO2 (g) and 1.00 mole of O2 (g) are added to a 1.00-L container and react until equilibrium is achieved at 1000 K. At equilibrium, the container has 0.919 moles of SO3 (g). What are Kc and Kp for the following reaction? 2 SO2 (g) + O2 (g) ⇄ 2 SO3 (g) A) Kc = 2.90, Kp = 238 B) Kc = 2.90, Kp = 2.90 C) Kc = 238, Kp = 238 D) Kc = 238, Kp = 2.90 E) None of the above is the correct answer.

D) Kc = 238, Kp = 2.90

What is the equilibrium constant expression for the following reaction? H2(g) + I2(g) ⇌ 2 HI(g) A) Kp = PHI/PH2PI2 B) Kp = [HI]2/[H2][I2] C) Kp = P2HI/P2H2P2I2 D) Kp = P2HI/PH2PI2 E) Kp = PH2PI2/P2HI

D) Kp = P2HI/PH2PI2

Keq=[CO]4/[Ni(CO)4] Which of the following reactions does the equilibrium constant shown above belong to? A) 2Ni(CO)4(g) ⇄ 2NiCO2(g) + 4CO(g) B) Ni(s)+ 4CO(g) ⇄ Ni(CO)4(g) C) 2Ni(CO)4(g) ⇄ 2Ni(s) + 8CO(g) D) Ni(CO)4(g) ⇄ Ni(s) + 4CO(g) E) Ni(CO)4(g) ⇄ 4CO(g)

D) Ni(CO)4(g) ⇄ Ni(s) + 4CO(g)

Consider the decomposition reaction of iodine bromide, which produces molecular bromine and iodine, with the equilibrium constant Kc = 2.5 × 10−3. The initial concentration of each of the three species is 0.05 M. What is the value of Q at that time 2 IBr(g) ⇌ Br2(g) + I2(g) A) Q = 0 B) Q = 0.5 C) Q = Kc D) Q = 1.00

D) Q=1.00

What is the expression for Kc for the following reaction? NH4Cl(s) ⇄ HCl(g) + NH3(g) A) 1/[HCl][NH3] B) [NH4Cl] C) [HCl][NH3]/[NH4Cl] D) [HCl][NH3] E) [NH4Cl]/[HCl][NH3]

D) [HCl][NH3]

Which of the following is a way to perturb a system at equilibrium? A)Changing the temperature. B) Adding or removing one or more of the reactants or products. C) Changing the pressure if one or more components is a gas. D) Changing the volume if one or more components is a gas. E) All of the above are ways to perturb an equilibrium.

E) All of the above are ways to perturb an equilibrium.

Phase changes are spontaneous processes since they happen without outside intervention at a certain temperature

False

Spontaneous processes always happen quickly T/F

False

The third law of thermodynamics says that the entropy of a perfectly crystalline substance at 0 degrees celsius is zero. T/F

False

True or False: The concentrations of reactants and products are always equal at equilibrium.

False

True/False: The concentration of gaseous species should not be included in the expression for Kc

False

a positive enthalpy change corresponds to heat given off during a process T/F

False

In the Diatomic nonmetals, which are gasses?

H2,N2,O2, F2,Cl2

In the diatomic nonmetals, which is a solid?

I2

For the reaction N2(g) + O2(g) ⇄ 2 NO(g) Kc = 4.0 at a particular temperature. What is Kc for the reaction given below? NO(g) ⇄ 1/2 N2(g) + 1/2 O2(g)

Kc = 0.50

a reaction that is spontaneous, large equilibrium constant

Keq > 1

What is the expression for the equilibrium constant for the following reaction? C(s) + H2O(g) ⇄ CO(g) + H2(g)

Keq= [CO][H2]/[H2O]

For the reaction FeO(s) + CO(g) ⇄ Fe(s) + CO2(g) the equilibrium constant expression is Kc = [CO2]/[CO] A) True B) False

True

In order for a process to be considered spontaneous, the free energy change of the system must be negative. T/F

True

Nickel (II) oxide reacts with carbon monoxide to form nickel metal. CO(g) + NiO(s) ⇄ CO2(g) + Ni(s) Kp = 20 at 873 K If the reaction vessel contains some solid Ni and NiO, 400 mm Hg of CO2 and 20 mm Hg of CO, all at equilibrium, doubling the amount of CO(g) present will lead to the reduction of more nickel oxide at 873 K. A) True B) False

True

True or False: If the total available amount of a solid or a pure liquid is consumed before an equilibrium is established, then an equilibrium state can never be attained (in other words, the activity of a solid or a pure liquid is only 1 if it is present in sufficiently large quantities). A) True B) False

True

True or False: In a dynamic equilibrium, the reactants are being converted into products at the same rate that products are being converted back into reactants.

True

True or False: Kp and Kc are related through the ideal gas law. A) True B) False

True

True or False: The equilibrium constant Keq changes with temperature. A) True B) False

True

True or False: The quotient given by the equilibrium concentration of products divided by reactants (each raised to the power of the corresponding stoichiometric coefficients) is constant.

True

When measuring the temp change of a reaction, the products of the reaction are considered part of the system

True

a higher temp. correlates with a higher molecular speed T/F

True

a qualitative T-diagram is used to predict the sign of the free energy change in a reaction by drawing arrows representing first the sign of the enthalpy change, and then the sign of the (-T delta S) term. T/F

True

a reaction can only said to be spontaneous under a certain set of conditions; if the conditions change, the reaction may no longer be spontaneous

True

all of these processes lead to an increase in standard entropy T/F: melting vaporization sublimation temp. increase reaction resulting in a greater number of gas molecules

True

entropy is defined as a measure of the # of specific ways in which

a thermodynamic system may be arranged

Spontaneity is important because it affects the....

ability of a process to do work

not only does the entropy of a single phase increase as heat is added, but the entropy also increases during phase transitions even though temperature is constant. The entropy change during a phase change is equal to the

amount of heat transferred at a fixed temperature.

Diatomics are __________________________________

atomic gasses

a non spontaneous reaction

cannot occur of itself without outside intervention (by the surroundings providing energy, doing work, or changing the reaction conditions)

a reaction is spontaneous if it is..

capable of proceeding in the forward direction to a substantial extent under a given set of conditions

Enthalpy (H) is heat transferred at ___________ pressure

constant

as temp. decreases,kinetic energy __________, and the # of and amplitude of the motions will _____________

decrease, decrease

the universe tends towards.....

disorder

entropy is the amount of......

disorder in a system

+ delta H...

endothermic: requires addition of heat

Each rotational state is another

energy state for the molecule.

Standard Molar Entropy (S with the o subscript):

entropy of a substance in its standard state (at 1 atm pressure and 298K with solutions in concentrations of 1M) in units J/mol K

the extent of a reaction (how much products are formed to reactants) reaches a maximum when the forward rate is _______________ to the reverse rate (equilibrium)

equal

if S universe is zero,then the process is at __________________

equilibrium and isnt spontaneous

in order to compare one substance to another in a process or reaction, we must do so under ______________________________

equivalent conditions

-delta H...

exothermic: heat is produced

The spontaneity of a chemical reaction or process is related to the.....

extent to which it takes

By definition, nature tends to move spontaneously....

from a state of lower probability to one of higher probability

For a given substance, which phase has the largest standard entropy? liquid crystalline solid gas aqueous

gas

What are the standard states of the elements? Noble gasses (nonmetals).... ____________________

gasses

As the number of atoms in a molecule increases, the number of possible vibrational states ____________________

increases

as temp increases, entropy ________

increases

for a spontaneous process the path between the reactants and products is.....

irreversible

At 1173 K, Keq = 0.0108 for the following reaction: CaCO3(s) ⇄ CaO(s) + CO2(g) The reaction takes place in a 10.0 L vessel at 1173 K. If a mixture of 15.0 g CaCO3, 15.0 g CaO, and 4.25 g CO2 are allowed to approach equilibrium, what will happen to the amount of CaCO3? A) It will increase B) It will decrease C) It will remain the same D) Not enough information is provided to answer this question

it will increase

Temperature affects the entropy of a system by changing the

kinetic energy of the particles.

a system that has (more/less) microstates, will have (more/less) entropy, and be more ordered

less, less

gas phase of a substance has more entropy than its ____________ phase, which has more entropy than a __________ phase

liquid, solid

we must do work in order to make things more....

more ordered

the _________ unique the "picture", under _____________ conditions(n,T,P are constant), the greater the # of possible microstates

more, identical

The (more/less) possible microstates, the (more/less) disordered the system, and increasing its entropy

more, more

when enthalpy change is positive and entropy change is negative, is the process spontaneous?

no, it is non-spontaneous at all temp.

at equilibrium the reaction process is ___________________ spontaneous. and some/no work done to the system or by system

not no

In general, a spontaneous process proceeds only in one direction

one direction, to a substantial extent, and releases or absorbs energy in the form of work or heat (or both)

Nature tends to go from states of low probability (_________) to states of high probability (_________)

order disorder

microstates can be thought of as.....

pictures pictures of the position and kinetic energy of every particle at one moment in time under a set of conditions

The entropy change is ___________ during a phase transition even though the temperature is constant.

positive

in order to decide the spontaneity process, we must consider the ______________________ that a process will occur

probability

Spontaneity has nothing to do with the ____________ at which a reaction will occur

rate

When a system is at equilibrium reactants and products can.....

reverse

an irreversible process can't be....

reversed to restore the system and surroundings to the original state. Work required to restore system to the original conditions

In the diatomic nonmetals, other non-metals are _________________

solids

What are the standard states of the elements? Metal: all are________

solids

What are the standard states of the elements? Metalloids: all are ____________

solids

moving to a less ordered state is ___________________ , while moving to a more ordered state is _____________________

spon, non spon

if S universe is positive then... the process is ____________________________________________________________

spontaneous in the forward direction

the more ordered state is less likely to occur

spontaneously

energy is a ___________ function; it is independent of the path taken

state

Translational, vibrational and rotational energy modes are ways of___________ energy.

storing

Third Law of thermodynamics:

the absolute entropy of a substance is = to zero at a temp. of absolute zero. There is perfect order in the system, so there is no entropy

What is entropy?

the amount of disorder in a system

The second law of thermodynamics is.....

the change in entropy of the universe always increases in a spontaneous process

thermodynamics explores....

the connection between energy and the extent of a reaction, but it does not give information about reaction rate

Microstates....

the different arrangements of a system. a single possible arrangement of the positions and kinetic energies in a system

Rotational energy is

the energy associated with the rotation of a molecule about an axis.

The standard free energy of a reaction is...

the free energy for a reaction when it occurs under standard- state conditions

Translational energy is

the kinetic energy of motion.

Vibrational energy is the

the periodic oscillation (movement back and forth) of atoms in a molecule

The first law of thermodynamics:

the total energy in the universe is constant. Energy cannot be created or lost

direction and extent is thermo/kinetics

thermo

nonlinear molecules have __________ possible rotational states

three

Each microstate will have the same _______________________________________________________________, but the energy will be __________________________________________________, among the various types of motions of the particles ( which include)

total energy, distributed differently, translate vibrate rotate

For linear molecules, there are ___________ possible

two possible rotational states

Which of these is not a non-spontaneous process? A) the conversion of rust back into iron metal at room temp. B) water freezing at room temp. C) sodium hydroxide reacting with hydrogen gas to produce sodium metal and water D) water freezing at -10 degrees celsius E) a ball rolling uphill

water freezing at -10 degrees celsius

The main reason for our interest in spontaneity is due to the fact that a spontaneous reaction can do

work