Homework answers / question archive / Complete whole packet of homework

Complete whole packet of homework

Chemistry

Share With

---

Complete whole packet of homework. No need to show work for multiple choice questions, but please show full work for non multiple choice questions
 

1. Carbon dioxide can degrade into carbon monoxide and oxygen according to the following equation:

2 CO2 (2,5 4— 2 CO ee, + I O2G2,

It has a Ke of 2.0 x 10° at 35°C. Which of the following is true for the forward reaction initially at 35°C, if it contains .15M CO2(g), 5.0M CO ¢,, and 2.5M 02;

(A) AG <0 (B) AS=0 (C) AG’ <0 (D)AG>O (E)AG =0

2. The following chemical reaction takes place in a closed, insulated container, with no heat entering or leaving the system:

f

Energy + NaNO3;,, — Na?! (ag) # NOx! (agpot L ft |

Which of the following conditions below ts true regarding this reaction?

Energy Entropy

(A) Remains constant Remains constant

(B) Remains constant Decreases

(C) Remains constant Increases

(D) Decreases Increases

(E) Increases Decreases

3. Which of the following reactions would we expect to have a positive AS''?

a. CQO2(g) — CO: (s)

b. HCI (g) + NH3 (g) — NHGCL (s)

c. Pb?* (aq) + 2CI (aq) — PbCl2 ()

d. 2 Ca (s) + O2(g) — 2 CaO {s)

( e. 2 KCIO3{(s) — 2KCI (s) + 3 O2 (g)

4. If a reaction proceeds non-spontaneously from initial standard state conditions, which of

the following mathematical relationships must be true?

a. AG >Oand Keg > | b. AG’ > O and Keg < 1

c. \G <Qand Keg > | d.AG <0 and Keg < }

e. AG =Oand Keg = !

5. CH30Ha, — CH30H

When methanol boils at 64.7 degrees C and | atmosphere of pressure according to the above reaction, which of the following mathematical relationships is true?

a. AH <Q, AS >0, AV>0O b. AH <0, AS <0, AV>0

c. AH >0, AS <0, AV<0 d. AH > 0, AS > 0, AV >0

e. AH >0, AS >0, AV <0

6. AS is negative for which of the following reactions?

1. Ca(NQ3)2 (aq) + Na2SO4 (aq) — CaSOxz(s)+2 NaNOs (aq)

2. C5H12 (1) — CsHi2 (g)

3. KBr (aq) > K*! (aq) + Br’ (aq)

t Celli sOsfs) > 6 (8) + 6 Haig) +3 O2(8) |

3. 2NH3(g)—-N2(g) + 3H2(g)

(A) | only (B) i and 2 only (C) 1, 2, and 3 only

(D) 4 only (E) 4and 5 only

7, 2 Fe203(s) +3 C (s) — 4 Fe (s) + 3 CO: (g)

The reaction above is non-spontaneous at room temperature, or 25°C. However, it becomes spontaneous at higher temperatures. Which of the following statements is true regarding this reaction at 25°C?

(A) AG, AH, and AS are all positive.

(B) AG, AH. and AS are all negative.

(C) AG and AH are negative, but AS is positive.

(D) AG and AS are negative, but AF/ is positive.

(E) AG and AH are positive, but AS is negative.

8. The standard molar free energies of formation (\G;") of MgO (s), HCI ( g), MgCl> (s) and

HO (g) are -569.57 kJ, -95 kJ, -592.33 kJ and -228.61 kJ, respectively. What is AG? for

‘ the reaction below at 298 K?

MeO (s) + 2HCI (g) — MgCl. (s) + H20 (g)

(A) -1486 kJ/mol (B) -156.4 kJ/mol (C) +61.37 kJ/mol

(D) -61.37 kJ/mol (E) -441.4 kJ/mol!

 

9. Solid potassium chlorate, KC1O;, decomposes into solid KC] and elemental oxygen gas at room temperature (25°C). If the surrounding air becomes warmer as a result, which of the following mathematical relationships regarding this reaction is true?

 

4H AS

(A) Positive Positive

(B) Positive Negative

(C) Positive ZETO

(D) Negative Positive

(E) Negative Negative

10. The value of AG” at 25° C for the formation of calcium chloride from its constituent i elements:

| Ca (s) r Clrig) + CaCl (s} | !

1S kJ/mol.

 

At 25.0°C for this reaction, AH* is —-795.8kJ/mol, and AS: is —159.8]/K.

 

(A) -748.2 kJ/mol (B) -4791 kJ/mol (C) +3199 kJ/mol

 

(D) -48,420 kJ/mol ,; (E) +77.35 kJ/mol

Section II: Directions: Write your response in the space provided following each question.

Examples and equations may be included in your responses where appropriate. For ( calculations, clearly show the method used and the steps involved in arriving at your answers. You must show your work to receive credit for your answer. Pay attention to

significant figures. (70 points total)

1. Given the spontaneous reaction at 25°C below: |

4HCi (g) + 1 O2(g)<—» 2Cl2 (g) + 2H20 (g) AH’ =-114.4 kJ

a. For this reaction, indicate whether the standard entropy change, \S’, is positive, negative, or zero. Justify your answer.

b. Which factor, the change in enthalpy, AH’, or the change in entropy, AS’, provides the principle driving force for the reaction at 298 K? Explain.

| 3 | |

c. For the reaction, how is the value of the standard free energy change, \G*, affected by an increase in temperature? Explain.

d. Given that this reaction is spontaneous (has a negative AG’) at 25°C, what conclusions can be made regarding the rate of this given reaction at 25°C? Explain your answer!

2. Hydrogen can be generated for fuel using graphite and steam as reactants, according to the spontaneous reaction at 25°C below:

C (s) + H20 (g) «——» 1 CO2(g) + H2(g)

AH’ = +131.3 kJ/mol and AS" = +150.3 J/K- mol at 298K.

For the reaction at 25 C, the value of the standard free-energy change, AG’, is

+93.3 kJ/mol.

a. Calculate the value of the equilibrium constant, Kg, for the reaction at 25°C.

b. Does the value of AG’ become more negative, less negative, or remain unchanged as the temperature is increased? Explain your answer!

:

|

| C. siver the following ‘aforlnation, calculate the value of the vada molar entropy, S’, for |

H20 (g) at 25°C.

Substance Entropy at 25°C (S°)

C 6s) + 6.0 J/K e mol

CO? (2) + 214.0 J/K ¢ mol

H2 (2) + 131.0 J/K e mol

FAK J fl | meter |

Cd (an) Ag

salt

bridge

IM Cd(NO 3)o, [M AgNO;,

100 milliliters L00 milliliters

The spontaneous reaction that occurs when the cell above operates is:

2 Agt + Cds) -» 2 Agis) + Cd2+ |

Answer questions 1-4 based on the diagram:

(A) Voltage increases.

(B) Voltage decreases but remains above zero.

(C) Voltage becomes zero and remains at zero.

(D) No change in voltage occurs.

(E) Direction of voltage change cannot be predicted without additional information.

Which of the above occurs for each of the following circumstances?

: 1. A50-milliliter sample of a 2-molar Cd(NO3)2 solution is added to the left beaker.

2. The silver electrode is made larger.

| 3. The salt bridge is wPipee by a platinum wire. | | |

4. Current is allowed to flow for 5 minutes.
5. If5789.1 coulombs is passed through an electrolytic cell containing a solution of In3+ ions, the

maximum number of moles of In that could be deposited at the cathode is: {

(A) 0.010 mole (B) 0.060 mole (C) 0.020 mole (D) 0.18 mole

(E) 0.030 mole

6. Fe2+ + 2e— > Feis) E* = -0.44 volt

Ni2+ + 2e—— Nis) E* = -0.23 volt

The standard reduction potentials for two half reactions are given above. The Nernst equation

for a galvanic cell at 25°C in which Fes) reduces Ni2* is the following:

E°= RTInK

nF

What is the equilibrium constant for the reaction below?

Fe(s) + Ni2* — Fe2+ + Nivs)

a. 1.9x10-23 sb 3.6x10*3 c. 5.2x10+22 d.7.6x10-8 ee. 1.3x10*?

7, Zn(s) + Cu2+ > Zn2+ + Cus)

| a electrolytic cell based on the reaction represented stlove was constructed from zinc and

copper half—cells. The observed voltage was found to be 1.00 volt instead of the standard cell potential, E, of 1.10 volts. Which of the following could correctly account for this

observation?

(A) The copper electrode was larger than the zinc electrode.

(B) The Zn++ electrolyte was Zn(NO3)2, while the Cu2+ electrolyte was CuSOg.

(C) The Zn2+ solution was more concentrated than the Cu2+ solution.

(D) The solutions in the half—cells had different volumes.

(E) The salt bridge contained KC! as the electrolyte.

8. What is the maximum mass of copper that could be plated out by electrolyzing aqueous CuCl» for 16.0 hours at a constant current of 3.00 amperes? (1 faraday = 96,500 coulombs)

(A) 28 grams (B) 57 grams (C) 64 grams (D) 114 grams (E) 128 grams

9. A direct-current power supply of low voltage (less than £0 volts) has lost the markings that

, indicate which output terminal is positive and which is negative. A chemist suggests that the

power supply terminals be connected to a pair of platinum electrodes that dip into 0.1—molar

KI solution. Which of the following correctly identifies the polarities of the power supply

terminals?

(A) A gas will be evolved only at the cathode.

(B) A gas will be evolved only at the anode.

(C) A gas will be evolved at both the cathode and anode.

(D) A metal will be deposited on the cathode.

(E) None of the methods above will identify the polarities of the power supply terminals.

Questions 10-1] refer to an electrolytic cell that involves the following half-reaction.

AIFg-3 +3 e — Al+6F-

10. Which of the following occurs in the reaction?

(A) AIFs * (or Al*?) is reduced at the cathode.

(B) Al is oxidized at the anode.

(C) Aluminum is converted from the -3 oxidation state to the 0 oxidation state.

(D) F acts as a reducing agent.

(E) F is reduced at the cathode.

| II. fi steady current of 10 amperes is passed through an alunjinum-production celi for 15 minutes. |

hich of the following is the correct expression for calculating the number of grams of

aluminum produced? (1 faraday = 96,500 coulombs)

(A) (10)(13)(96,500) g (B) — CO)U1S5)27) g

(27)(60) (60)(96,500)

(C) (10)(15)(60)(27) g (D) = (96,500)(27) g

(96,500)(3) (60)(96,500)

(E) (27)(3) g

(96,500)(10)(15)(60)

Section II: CLEARLY SHOW THE METHOD USED AND THE STEPS INVOLVED IN ‘

 

ARRIVING AT YOUR ANSWERS. It is to your advantage to do this, since you may

 

obtain partial credit if you do and you will receive little or no credit if you do not.

 

Attention should be paid to significant figures. 5 points each (60 points total)

 

1. In an electrolytic cell, a current of 0.250 ampere is passed through a solution of a chloride of

 

iron, producing Fers) and Clg).

 

(a) Write the equation for the half-reaction that occurs at the anode.

 

(b) When the cell operates for 2.00 hours, 0.521 gram of iron is deposited at one electrode.

Determine the formula of the iron chloride compound in the original solution.

 

(c) Write the balanced equation for the overall reaction that occurs in the cell.

 

py |

 

{d) How many liters of Clog), measured at 25°C and 750 mm Hg, are produced when the cell operates as described in part (b) ?

 

(e) Calculate the number of grams of chlorine gas that can be produced from the solution if 2.7 Ampere are run through the soiution for 1.00 hour.

2. Answer the following questions that relate to electrochemical reactions.

 

(a) Under standard conditions at 25°C, Zn(s) reacts with Co2+/ag) to produce Covs).

(i) Write the balanced equation for the oxidation half reaction.

(ii) Write the balanced net-ionic equation for the overall reaction.

(111) Calculate the standard potential, E”, for the overall reaction at 25‘C.

 

(b) At 25°C, H20} decomposes according to the following equation: |

 

2 H202(aq) > 2 H2O0W) + Oxg) E° =0.55 V

(i) Determine the value of the standard free energy change, AG’, for the reaction at 25°C.

Assume the number of moles of electrons transferred is 2.

 

(i) Determine the value of the equilibrium constant, Keg, for the reaction at 25°C.

(iii) The standard reduction potential, £’, for the half reaction: j

Ox) +4 H*+(aq) +4de-—2 H,Ow

has a value of 1.23 V. Using this information in addition to the information given above, determine the value of the standard reduction potential, E” for the half reaction below:

O2g) + 2 Ht(aq) + 2 e- 3 HzO x(a9)

 

(c) In an electrolytic cell, Cuys) is produced by the electrolysis of CuSOgrag:. Calculate the maximum mass of Cus) that can be deposited by a direct current of 100. amperes passed through 5.00 L of 2.00 M CuSOygreq) for a period of 1.00 hour.