CELDA ELECTROQUIMICA (CELDA DE DANIELL) y FUERZA ELECTROMOTRIZ (FEM)

What are Electrochemical Cells?

Introduction to Electrochemical Cells

• The video introduces electrochemical cells, explaining their function and the concept of electromotive force.

• A spontaneous reaction is demonstrated when a zinc bar is placed in a copper(II) solution, leading to the deposition of metallic copper on the zinc.

Oxidation and Reduction Reactions

• The process involves oxidation-reduction (redox) reactions where elemental zinc oxidizes to Zn²⁺ ions while Cu²⁺ ions reduce to elemental copper.

• Key definitions:

• Oxidation: Loss of electrons (zinc).

• Reduction: Gain of electrons (copper).

Semi-Reactions in Redox Processes

• The overall redox reaction can be split into half-reactions:

• Oxidation half-reaction: Zinc loses electrons.

• Reduction half-reaction: Copper gains electrons.

• Emphasizes that oxidation and reduction occur simultaneously; one cannot happen without the other.

Structure and Function of Electrochemical Cells

Components of an Electrochemical Cell

• An electrochemical cell consists of two compartments called half-cells, each containing an electrode submerged in an ionic solution.

• Electrons flow through an external circuit connecting the electrodes, facilitating electric current generation.

Role of Salt Bridge

• A salt bridge connects the two half-cells, maintaining charge balance by allowing ion flow as electrons circulate.

• The electrode where oxidation occurs is termed the anode, while the cathode is where reduction takes place.

The Daniel Cell Explained

Construction and Operation

• The Daniel cell features a zinc electrode in a zinc sulfate solution and a copper electrode in a cupric sulfate solution connected by a U-shaped salt bridge with inert electrolyte.

• When operational, electrons flow from zinc to copper, generating electric current observable via a voltmeter.

Chemical Reactions in Action

• In this setup:

• Zinc oxidizes to Zn²⁺ ions releasing two electrons.

• Copper(II) ions reduce to solid copper deposited on the cathode.

Overall Reaction and Representation

Global Reaction Summary

• The complete reaction shows that zinc reacts with copper(II), producing Zn²⁺ ions and depositing elemental copper.

Diagrammatic Representation

Electrochemical Cells and Their Functionality

Structure of Electrochemical Cells

• The diagram of an electrochemical cell is divided by a double bar, representing the boundary between oxidation and reduction half-cells. This double bar typically symbolizes salt bridges.

• In a Daniel's cell, the anode (zinc) and cathode (copper) are clearly defined, with oxidation occurring at the zinc electrode and reduction at the copper electrode, separated by a salt bridge.

• The zinc electrode interacts with Zn²⁺ ions in solution, while the copper electrode is in contact with Cu²⁺ ions, each having specified molar concentrations.

Electrons Flow and Potential Difference

• Electricity in electrochemical cells arises from electron flow from the anode to the cathode due to a potential difference between electrodes.

• This potential difference is termed electromotive force (emf), denoted as 'E', measured using a voltmeter across electrodes in volts.

Spontaneity of Reactions

• A positive emf indicates that reactions are spontaneous; this relates to free energy changes where spontaneous processes result in decreased free energy.

• Standard conditions for measuring emf include 1 M concentration for solutions or 1 atm pressure for gases at 25°C.

Standard Cell Potential