Exam #4 Flashcards
In the redox reaction: Zn + Cu²⁺ → Zn²⁺ + Cu, which species is reduced?
A) Zn
B) Cu
C) Zn²⁺
D) Cu²⁺
D) Cu²⁺
Which of the following is the oxidizing agent in the reaction: 2Fe³⁺ + 2I⁻ → 2Fe²⁺ + I₂?
A) Fe³⁺
B) Fe²⁺
C) I⁻
D) I₂
A) Fe³⁺
When balancing a redox reaction in acidic solution, what must be added to balance oxygen atoms?
A) H⁺
B) H₂O
C) OH⁻
D) e⁻
B) H₂O
Which part of a galvanic cell is the site of oxidation?
A) Anode
B) Cathode
C) Salt bridge
D) Voltmeter
A) Anode
In a galvanic cell, which direction do electrons flow?
A) From cathode to anode
B) From anode to cathode
C) Both directions
D) No flow
B) From anode to cathode
A reduction potential of +1.23 V means the substance:
A) Is easily oxidized
B) Is a strong reducing agent
C) Is likely to be reduced
D) Is neutral
C) Is likely to be reduced
If E°(cathode) = +0.80 V and E°(anode) = +0.34 V, what is the cell potential?
A) +1.14 V
B) +0.46 V
C) -0.46 V
D) -1.14 V
B) +0.46 V
Which of the following affects the rate constant (k) in the rate law equation?
A) Concentration
B) Catalyst
C) Temperature
D) Both temperature and catalyst
D) Both temperature and catalyst
rate increases, but rate constant remains the same in concentration
If doubling the concentration of A doubles the rate, the order of the reaction with respect to A is:
A) Zero
B) First
C) Second
D) Cannot be determined
B) First
What is the half-life formula for a first-order reaction?
A) t½ = 0.693/k
B) t½ = [A]₀/2k
C) t½ = k/[A]₀
D) t½ = 2k
A) t½ = 0.693/k
Which of the following statements about catalysts is true?
A) They are consumed in the reaction
B) They decrease the rate of reaction
C) They lower activation energy
D) They increase equilibrium constant
C) They lower activation energy
In the reaction mechanism: A → B → C, B is:
A) Reactant
B) Product
C) Intermediate
D) Catalyst
C) Intermediate
What is the reducing agent in the reaction: Cl₂ + 2Br⁻ → 2Cl⁻ + Br₂?
A) Cl₂
B) Br⁻
C) Cl⁻
D) Br₂
B) Br⁻
In acidic solution, which of the following is needed to balance hydrogen atoms in a redox reaction?
A) OH⁻
B) H₂
C) H⁺
D) H₂O
C) H⁺
Which of the following statements is true about a galvanic cell?
A) Electrons flow from cathode to anode
B) The cathode is negatively charged
C) The anode loses mass during the reaction
D) The salt bridge provides electrons
C) The anode loses mass during the reaction
Which component prevents charge buildup in a galvanic cell?
A) Voltmeter
B) Salt bridge
C) Electrodes
D) Power source
B) Salt bridge
Which of the following would be oxidized based on standard reduction potentials?
A) A species with +0.13 V
B) A species with +0.34 V
C) A species with -0.13 V
D) A species with +1.23 V
C) A species with -0.13 V
Electrolysis requires an external power source because the reaction is:
A) Spontaneous
B) Endergonic
C) Exothermic
D) Rapid
B) Endergonic
During electrolysis of molten NaCl, what is produced at the cathode?
A) Na⁺
B) Na metal
C) Cl₂ gas
D) H₂ gas
B) Na metal
Q: A reaction is second order with respect to A. If [A] is tripled, the rate increases by a factor of:
A) 2
B) 3
C) 6
D) 9
D) 9 (3^2 = 9)
In a first-order reaction, if the initial concentration of reactant is 1.0 M and after 1 half-life it’s 0.50 M, how much remains after 3 half-lives?
A) 0.25 M
B) 0.125 M
C) 0.0625 M
D) 0.50 M
B) 0.125 M
A galvanic cell is constructed with a zinc electrode in Zn²⁺ solution and a copper electrode in Cu²⁺ solution. The standard reduction potentials are: Zn²⁺/Zn = -0.76 V, Cu²⁺/Cu = +0.34 V. What is the standard cell potential, and which metal is oxidized?
A) 1.10 V; Cu is oxidized
B) 0.42 V; Cu is oxidized
C) 1.10 V; Zn is oxidized
D) -1.10 V; Zn is oxidized
C) 1.10 V; Zn is oxidized
A student measures the voltage of a galvanic cell as lower than the calculated standard potential. Which is a likely explanation?
A) The temperature is higher than standard conditions
B) The salt bridge is broken
C) The concentrations of reactants are lower than 1 M
D) The anode is larger than the cathode
C) The concentrations of reactants are lower than 1 M
During the electrolysis of water, twice as much hydrogen gas is produced compared to oxygen. Why?
A) Hydrogen has a lower molar mass
B) Hydrogen is produced at a faster rate
C) Two moles of H⁺ are needed for every mole of O²⁻
D) Water has more hydrogen than oxygen
C) Two moles of H⁺ are needed for every mole of O²⁻
You conduct an experiment and find that doubling [A] while holding [B] constant causes the rate to quadruple. What is the order of the reaction with respect to A?
A) Zero
B) First
C) Second
D) Third
C) Second
A reaction has the rate law Rate = k[A][B]². If [A] is cut in half and [B] is doubled, how does the rate change?
A) Increases by a factor of 2
B) Stays the same
C) Decreases by a factor of 2
D) Increases by a factor of 4
A) Increases by a factor of 2
You increase the temperature of a reaction mixture. What happens to the rate constant (k) and activation energy (Ea)?
A) k increases, Ea increases
B) k decreases, Ea increases
C) k increases, Ea stays the same
D) k increases, Ea decreases
A) k increases, Ea increases
You are studying a two-step reaction. Step 1 is fast and reversible. Step 2 is slow. Which determines the overall rate law?
A) Step 1
B) Step 2
C) The equilibrium constant of step 1
D) The final product concentration
B) Step 2
The standard reduction potentials are: Fe³⁺/Fe²⁺ = +0.77 V and Cu²⁺/Cu = +0.34 V. What is the standard cell potential for Fe³⁺ + Cu → Fe²⁺ + Cu²⁺?
A) +0.43 V
B) -0.43 V
C) +1.11 V
D) -1.11 V
A) +0.43 V
(subtract oxidized from reduced)
A galvanic cell has a standard potential of 1.10 V.
Under non-standard conditions at 25°C, the concentration of products is 1.0 M and reactants is 0.010 M.
The reaction involves 2 electrons transferred.
What is the cell potential under these conditions?
Constants:
R = 8.314 J/mol·K
F = 96,485 C/mol·e⁻
A) 1.04 V
B) 1.16 V
C) 0.94 V
D) 0.88 V
A) 1.04 V
