electrochemistry
For a voltaic cell:
Zn(s) → Zn2+(aq) +2e-
Cu2+(aq) +2e- → Cu(s)
What is being oxidized, reduced, the reducing agent, and the oxidizing agent?
Oxidized and reducing agent: Cu(s)
Reduced and oxidizing agent: Zn(s)
how do electrons flow in a voltaic cell?
from anode to the cathode!
Consider the following reaction in aqueous solution,
5Br-(aq) + BrO3- (aq) + 6H+(aq) → 3Br2(aq) + 3H2O(l)
If the rate of appearance of Br2 at a particular moment during the reaction is 0.025 M s-1, what is the rate of disappearance (in M s-1) of Br- at that moment?
0.042 M s-1
what is ΔG and Ecell when spontaneous?
ΔG < 0
Ecell > 0
What are the strong acids and bases?
H2SO4, HI, HBr, HNO3, HCl, HClO4,
LiOH, NaOH, KOH, RbOH, CsOH, Ca(OH)2, Sr(OH)2, Ba(OH)2
Pick the true statement:
1. The salt bridge allows the ions present in the two half-cells to mix extensively
2. Ions from the electrolyte in the salt bridge flow into each half-cell to maintain electrical neutrality.
3. Free electrons flow through the salt bridge to maintain electrical neutrality in the two half cells.
2. Ions from the electrolyte in the salt bridge flow into each half-cell to maintain electrical neutrality.
Find the lie:
1. In a galvanic cell, electrons flow from the anode to the cathode through an external circuit.
2. Oxidation always occurs at the anode, regardless of the type of electrochemical cell.
3. The salt bridge in an electrochemical cell is necessary to transport electrons between the two half-cells.
3. The salt bridge in an electrochemical cell is necessary to transport electrons between the two half-cells.
The salt bridge is for maintaining electrical neutrality by allowing IONS to flow between the two half-cells. Anions move to the anode and cations move to the cathode. Electrons travel through the external circuit.
Consider the following exothermic gas-phase reaction: 4HCl(g) + O2(g) ⇌ 2Cl2(g) + 2H2O(g)
Assuming the system is initially at equilibrium, what will happen to the number of moles of HCl(g) in a container of fixed volume if…
O2(g) is added
Cl2(g) is added
Some of the H2O(g) is removed
Pressure is increased
Decrease
increase
decrease
decrease
A voltaic cell consists of a Mn/Mn2+ electrode (Eo = -1.18V) and a Fe/Fe2+ electrode (Eo = -0.44V). Calculate [Fe2+] if [Mn2+] = 0.050M and Ecell = 0.78V at 25oC.
1.1M
What influences the rate of a chemical reaction performed in a solution?
a) Temperature
b) Activation energy
c) Presences of a catalyst
d) Concentrations of reactants
e) All of the above influence the rate
e) All of the above influence the rate
What is the reaction that occurs at the cathode of a voltaic cell if the overall reaction is
Sn(s) + 2Fe3+(aq) ⇌ Sn2+(aq) + 2Fe2+(aq)
Fe3+(aq) + e- ⇌ Fe2+(aq)
Calculate the standard cell potential (in V) for the following overall cell reaction,
Sn(s) + 2Fe3+(aq) ⇌ Sn2+(aq) + 2Fe2+(aq)
Fe3+(aq) + e- ⇌ Fe2+(aq); Eo = -0.14V
Sn2+(aq) + 2e- ⇌ Sn(s); Eo = +0.77V
+0.91V
For a particular chemical reaction, ΔHo is positive and ΔSo is negative. Which of the following is true?
a) The reaction will be spontaneous only if the magnitude of ΔHo is large enough to overcome the unfavorable entropy change.
b) The reaction will be spontaneous only if the magnitude of ΔSo is large enough to overcome the unfavorable entropy change.
c) The reaction will be spontaneous regardless of the magnitudes of ΔHo and ΔSo.
d) The reaction cannot be spontaneous.
e) The reaction will be spontaneous only if ΔGo is positive.
d) The reaction cannot be spontaneous.
Consider the following standard reduction potentials of the half reactions and find ΔG (in kJ) for the following reaction at 25oC.
I3-(aq) + 2e- ⇌ 3I-(aq); Eo = 0.53V
Cr3+(aq) + e- ⇌ Cr2+(aq); Eo = -0.41V
-181.391 kJ
The concentration of NaOH in water is gradually increased without changing the volume significantly. How does H3O+, OH-, pH, and pOH change?
H3O+ decreases, OH- increases
pH increases, pOH decreases
What is the reaction at the anode, the reaction at the cathode, and the number of mol of electrons transferred in a voltaic cell composed of a Cu(s)/CuSO4 anode and Ag(s)/AgNO3 cathode?
Reaction at anode: Cu(s) ⇌ Cu2+(aq) + 2e-
Reaction at cathode: Ag+(aq) + e- ⇌ Ag(s)
Number of mol of electrons transferred: 2
Consider these two half-cell reactions and their standard reduction potentials at 25oC.
Li+ (aq) + e- → Li(s); Eo = -3.05V
Ni2+ (aq) + 2e- → Ni(s); Eo = -0.28V
What is the Eo for the voltaic cell build with these half-reactions?
+2.77V
What are the tests of a reaction mechanism?
1. Do the elementary steps in the reaction mechanism sum to produce the
overall balanced chemical equation?
2. Does the experimentally‐determined rate law for the (overall) reaction have
the same form as the rate law for the rate‐determining step in the reaction
mechanism?
3. Are all of the elementary steps in the reaction mechanism either
unimolecular or bimolecular (termolecular elementary steps are very rare)?
Of the following half-reactions, which is the strongest reducing agent?
PbI2(s) + 2e- ⇌ Pb(s) + 2I-(aq); Eo = -0.365V
Ca2+(aq) + 2e- ⇌ Ca(s); Eo = -2.868V
Pt2+(aq) + 2e- ⇌ Pt(s); Eo = 1.18V
Br2(l) + 2e- ⇌ 2Br-(aq); Eo = 1.066V
Ca(s)
A decomposition reaction involving a single reactant has a rate constant, k, equal to 0.066 s-1. Calculate the time required (in seconds) for the concentration of the reactant to reach 19.4% of its initial value.
25s