A cell was prepared by dipping a Cu wire and a saturated calomel electrode into 0.10 M CuSO4 solution. The Cu wire was attached to the positive terminal of a potentiometer and the calomel electrode was attached to the negative terminal.(a) Write a half-reaction for the Cu electrode. (Use the lowest possible coefficients. Omit states-of-matter.) (c) Calculate the cell voltage.

(a)  Cu²⁺ +2e⁻ ⇌ Cu

(c) 0.07 V  

Explanation:

(a) Cu half-reaction

Cu²⁺ + 2e⁻ ⇌ Cu

(c) Cell voltage

The standard reduction potentials for the half-reactions are+

                                              E°/V

Cu²⁺ + 2e⁻ ⇌ Cu;                  0.34  

Hg₂Cl₂ + 2e⁻ ⇌ 2Hg + 2Cl⁻; 0.241

The equation for the cell reaction is

                                                                            E°/V

Cu²⁺(0.1 mol·L⁻¹) + 2e⁻ ⇌ Cu;                               0.34  

2Hg + 2Cl⁻ ⇌ Hg₂Cl₂ + 2e⁻;                             -0.241

Cu²⁺(0.1 mol·L⁻¹) + 2Hg + 2Cl⁻ ⇌ Cu + Hg₂Cl₂;   0.10

The concentration is not 1 mol·L⁻¹, so we must use the Nernst equation

(ii) Calculations:  

T = 25 + 273.15 = 298.15 K

definition

                    entropy is a measure of the randomness or the extent of disorder of a chemical process.

                      enthalpy is a measure of the heat change of a reaction occurring at a constant pressure.

measurement units:

                        entropy is measured in joule per kelvin (jk⁻¹)   whereas enthalpy is measured in joule per mole (jmol⁻¹)

requirements:

                            entropy has no requirements or limits, and its change is measured by the division between the heat change of the chemical process and the temperature.

                              in contrast, enthalpy can only be related to the heat change of the reaction under standard conditions.