A(voltaic) concentration cell is constructed using two zinc (zn) electodes and two aqueous solutions containing zn2+. if the concentrations of zn2+ in each of the two aqueous solutions are 1.25 m and 6.50 × 10-4 m, respectively, then the cell emf (ecell) is v.

a. −0.194
b. 0.194
c. −0.0972
d. 0.0972
e. 0.760

d. 0.0972

Explanation:

In a cell, a redox reaction happens, it means that one compound will reduce (gain electrons) and other will oxides (lose electrons). The reduction potential (E°) of a compound can be calculated by the redox between the compound and the hydrogen, which has E° = 0.00. As higher is the value of E°, as easy is for the compound to reduce. For a reaction, the value of E° = E° (the substance that reduces) - E°(the substance that oxides).

The cell emf can be calculated by the Nernst's equation:

Ecell = E° - (0.0592/n)*logQ

Where E° is the reduction potential of the cell (E°reduction - E°oxidation), n is the number of electrons being changing in the redox reaction, and Q is the reaction coefficient.

In this case, the cell is formed by the same compound, s E° = 0. Because Zn loses 2 electrons to form Zn⁺², n = 2, and the reaction must go from the highest concentration to the lowest, thus the reactant is where there's more Zn⁺², and the products where there's less Zn⁺²:

Q = [products]/[reactants]

Q = [Zn⁺²]less/[Zn⁺²]more

Ecell = -(0.0592/2)*log((6.50x10⁻⁴)/1.25)

Ecell = -0.0296*(-3.2840)

Ecell = 0.0972 V

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.