1.) for the reaction below: a. assign an oxidation state to each atom in the rea
ID: 860203 • Letter: 1
Question
1.) for the reaction below: a. assign an oxidation state to each atom in the reactants and each atom of the products. b. state which element is oxidized and which element is reduced. {Al(s) + 2Ag^+(aq) to Al^3+(aq) + 2Ag(s)} 2.) Use the half reaction method to balance the redox reaction below in acidic solution. Circle the oxidizing agent and put a box around the reducing agent. {BrO3^-(aq) + N2H4(g) to Br^-(aq) + N2(g)} 3.) Use information available in the appendix of your textbook to calculate both {delta S rxn degree} and {delta G rxn degree} for the following reaction at 298K. {K2CO3(s) to K2O(s) + CO2(g)}
Explanation / Answer
Ans 1)
Al(s) + 2Ag+(aq) ---> Al3+(aq) + 2Ag(s)
a) In LHS
oxidation number Al = 0
oxidation number Ag+1= +1
In RHS
oxidation number Al+3 = +3
oxidation number Ag = 0
b) Increase in oxidation number = oxidation
Al(s) IS OXIDIZED
Ag+ IS REDUCED
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2)
BrO3- (aq) + N2H4(g) ---------> Br- (aq) + N2(g)
Using half-reaction method:
Step 1: Half-reactions:
Reduction reaction: BrO3- ----> Br-
Oxidation reaction: N2H4 --> N2
REDUCING AGENT: N2H4
OXIDIZING AGENT: BrO3-
Step 2: Balancing O by adding H2O:
BrO3- ---> Br- + 3 H2O
N2H4 --> N2
Step 3: Balancing H by adding H+:
BrO3- + 6 H+ --> Br- + 3 H2O
N2H4 --> N2 + 4 H+
Step 4: Balancing charges by adding electrons:
BrO3- + 6 H+ + 6 e- --> Br- + 3 H2O
N2H4 --> N2 + 4 H+ + 4 e-
Step 5: Balancing the electrons in the two reactions by multiplying both reactions by numbers:
2 BrO3- + 12 H+ + 12 e- --> 2 Br- + 6 H2O (multiplied by 2)
3 N2H4 --> 3 N2 + 12 H+ + 12 e- (multiplied by 3)
Step 6: Adding the equations and simplifying:
2 BrO3- + 3 N2H4 --> 3 N2 + 2 Br- + 6 H2O
Answer: 2 BrO3- (aq) + 3 N2H4 (g) --------> 2 Br- (aq) + 3 N2 (g) + 6 H2O (l)
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Answer 3)
K2CO3(s) -------> K2O(s) + CO2(g)
Standard values
delHf for K2O = -363 kJ/mol
delHf for K2CO3 = -1150 kJ/mole
delta Hf for CO2 = -393.5 kJ/mole
delHo reaction = -363 -393.5 - (-1150)
= 393.5 kJ/mole
Standard values of entropy:
K2O: 94.03 J/molK
K2CO3: 155.52 J/molK
CO2: 213.79 J/molK
delSo reaction = Soproducts - Soreactants
= 94.03 + 213.79 - 155.52
= 152.3 J/molK (ans)
del Go = delHo - T * delSo
or del Go = 393500 - 298*152.3
or del Go = 348114.6 J/mol = 348.11 kJ/mole (ans)
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