Électrochimie - Concepts et Réactions

Electrochimie

• Conducteur électrique: A substance where charged particles can move under an electric field. Two types exist: electronic (charged particles are electrons) and ionic (charged particles are ions).
• Réaction électrochimique: A heterogeneous reaction involving charge transfer at the interface of two conductors. It involves molecules, atoms, ions, and electrons. It results in a change in conductive mode.
• Exemple de réaction électrochimique: Dissolution of iron metal in an acidic medium (Fe + 2H+ → Fe+2 + H2)
• Système électrochimique: Formed by the combination of an electronic conductor (electrode) and an ionic conductor (electrolyte). The contact surface between the two is called the interface.
• Conductivité: The ability of a solution to conduct an electric current. It's related to the solution's resistance (R) by the formula G = 1/R, where G is the conductance.
• Loi d'Ohm: In an electrolytic solution, the voltage (U) is proportional to the current (I) and the resistance (R) of the solution with the formula U = R × I.
• Conductivité spécifique: The conductivity of a given amount of electrolyte in a 1cm³ cube.
• Conductivité équivalente: The conductivity of a solution containing one equivalent gram (e.g. gram-equivalent) of electrolyte in a certain volume (V) where the distance between the electrodes is 1cm.
• Nombre de transport: The fraction of current carried by a particular ion type (ti) in a solution, calculated using the formula ti = Ii / I. It's related to the ionic conductivities.
• Loi de Kohlrausch: The conductivity of a solution is related to the concentrations of its ions and their conductivities in very dilute solutions.
• Activités ioniques: Corrected concentration values to account for interactions in solutions at non-infinite dilution.
• Force ionique (I): A measure of the ionic strength of a solution, related to the concentrations and charges of the ions present (I=1/2 ∑ c_iz_i²).

Activité et Conductivité

• Activité d'un ion: The effective concentration of an ion, taking into account the interactions with other ions in the solution.
• Activité d'un électrolyte: The product of the activities of the ions in an electrolyte.
• Coefficient d'activité: A correction factor relating the activity to the concentration (a = γ c, where a is the activity, γ is the activity coefficient, and c is the concentration).
• Exemples de conductivité spécifique et équivalente: Data tables demonstrating conductivity changes based on different concentrations and temperatures.
• Electrolytes faibles: Electrolytes that don't fully dissociate in solution, and their conductivity depends significantly on the solution's concentration.
• Electrolytes forts: Electrolytes that fully dissociate into ions in solution.
• Loi de Debye-Hückel: A relationship to estimate activity coefficients based on the force and concentration.

Exemple de dosage et conductimétrie

• Examples of applying conductivity measurements in titration.
• How conductivity changes with added titrant, particularly in weak acid and strong base titrations.
• Importance of controlling and accounting for temperature and other conditions