Chemistry Answers

Consider the cell, Zn(s)|ZnCl2(0.0050 mol kg−1)|Hg2Cl2(s)|Hg(l), for which the cell reaction is Hg2Cl2(s) + Zn(s) → 2 Hg(l) + 2 Cl−(aq) + Zn2+(aq). The cell potential is +1.2272 V, E⦵(Zn2+,Zn) = −0.7628 V, and E⦵(Hg2Cl2,Hg) = +0.2676 V. (a) Write the Nernst equation for the cell. Determine (b) the standard cell potential, (c) ΔrG, ΔrG⦵, and K for the cell reaction, (d) the mean ionic activity and activity coefficient of ZnCl2 from the measured cell potential, and (e) the mean ionic activity coefficient of ZnCl2 from the Debye–Hückel limiting law. (f) Given that (∂Ecell/∂T)p = −4.52 × 10−4 V K−1, Calculate ΔrS and ΔrH.

For a hydrogen/oxygen fuel cell, with an overall four-electron cell reaction 2 H2(g) + O2(g) → 2 H2O(l), the standard cell potential is +1.2335 V at 293 K and +1.2251 V at 303 K. Calculate the standard reaction enthalpy and entropy within this temperature range.

Write the equilibrium constant expression

1.     H2(g) + I₂(g) ⇌ 2HI(g)

2.     3O₂(g) ⇌ 2O₃(g)

3.     2CO₂(g) ⇌ 2CO(g) +O₂(g)

4.     CH₃COOH (aq) +C₂H₅OH ⇌ CH₃COOC₂H₅(aq) +H₂O(l)

5.     AgCl(s) ⇌ Ag+ (aq) Cl (aq)

One ecologically important equilibrium is that between carbonate and hydrogencarbonate (bicarbonate) ions in natural water. (a) The standard Gibbs energies of formation of CO32−(aq) and HCO3−(aq) are −527.81 kJ mol−1 and −586.77 kJ mol−1, respectively. What is the standard potential of the HCO3−/CO32−,H2 couple? (b) Calculate the standard potential of a cell in which the cell reaction is Na2CO3(aq) + H2O(l) → NaHCO3(aq) + NaOH(aq). (c)Write the Nernst equation for the cell, and (d) predict and calculate the change in cell potential when the pH is changed to 7.0 at 298 K.

A fuel cell is constructed in which both electrodes make use of the oxidation of methane. The left-hand electrode makes use of the complete oxidation of methane to carbon dioxide and liquid water; the right-hand electrode makes use of the partial oxidation of methane to carbon monoxide and liquid water. (a) Which electrode is the cathode? (b) What is the cell potential at 25 °C when all gases are at 1 bar?

Tabulated thermodynamic data can be used to predict the standard potential of a cell even if it cannot be measured directly. The standard Gibbs energy of the reaction K2CrO4(aq) + 2 Ag(s) + 2 FeCl3(aq) → Ag2CrO4(s) + 2 FeCl2(aq) + 2 KCl(aq) is −62.5 kJ mol−1 at 298 K. (a) Calculate the standard potential of the corresponding galvanic cell and (b) the standard potential of the Ag2CrO4/Ag,CrO42− couple.

Use the information in the Resource section to calculate the standard potential of the cell Ag(s)|AgNO3(aq)||Cu(NO3)2(aq)|Cu(s) and the standard Gibbs energy and enthalpy of the cell reaction at 25 °C. (ii) Estimate the value of ΔrG⦵ at 35 °C.

Calculate the standard potential of the cell Pt(s)|cystine(aq),

cysteine(aq)|| H+(aq)|O2(g)|Pt(s) and the standard Gibbs energy of the cell reaction at 25 °C. Use E⦵ = −0.34 V for cystine(aq) + 2 H+(aq) + 2 e− → 2 cysteine(aq).

What mass of nitrogen is needed to react with 21.25 g of hydrogen?

If the hydrogen ion concentration of an unknown solution is 4.56E-7, what is its pH and will this form an acid or a base?