Use the unbalanced redox reaction below to answer questions 6-8 Fe(s) + CrO^2-_4

Question

Use the unbalanced redox reaction below to answer questions 6-8 Fe(s) + CrO^2-_4 (aq) rightarrow Fe^3+ + CrO_2(aq) (basic media) The oxidation state of chromium changes from ______ to ______ a. 4 to 2 b. 4r to 0 C. 6 to 4. d. 6 to 2 e, 6 to 5 The reducing agent is _______ a. Fe(s) b. CrO^2- _4 (aq) c. Fe^3+ d. CrO_2 (aq) When the equation is balanced the coefficient in front of CH^- is a. 2 b, 6 c. 10 d. 12 e. 14 When the standard free energy of a reaction delta G is negative we know which of the following is always true? A. The entropy of the universe is increasing B. The delta H degree is negative C. The delta S^degree _system is positive D. K_eq > 1 A. A only B. A and B only C. B and C only D. A and D only E. all are true

Explanation / Answer

Balance

Fe = Fe+3

CrO4-2 = CrO2

balance O

Fe = Fe+3

CrO4-2 = CrO2 + 2H2O

balnace H

Fe = Fe+3

4H+ + CrO4-2 = CrO2-2 + 2H2O

balance charge

Fe = Fe+3 + 3e-

4e- + 4H+ + CrO4-2 = CrO2-2 + 2H2O

balance e-

4Fe = 4Fe+3 + 12e-

12e- + 12H+ + 3CrO4-2 = 3CrO2-2 + 12H2O

add all

4Fe + 12H+ + 3CrO4-2 = 3CrO2-2 + 12H2O +  4Fe+3

add OH-

4Fe + 12H2O + 3CrO4-2 = 3CrO2-2 + 12OH- +  4Fe+3

now,

Cr goes from +6 to +2

Q7.

reducing agent --> is oxidizing so choose Fe(s)

Q8

OH -- 12 coefficient

Q9.

dG < 0

then

entropy always increaes, dH cna't be sure, dSsystem cant be sure, KEq > 1

so only A and D are true

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