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Questions and Answers
What is the main function of the Standard Hydrogen Electrode in electrochemistry?
What is the main function of the Standard Hydrogen Electrode in electrochemistry?
Which type of battery is specifically known for its usage in small electronic devices due to its compact size and rechargeable capability?
Which type of battery is specifically known for its usage in small electronic devices due to its compact size and rechargeable capability?
Which factor is NOT commonly associated with hastening the rusting process of iron?
Which factor is NOT commonly associated with hastening the rusting process of iron?
What is the primary purpose of electrolysis in water?
What is the primary purpose of electrolysis in water?
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Which process is associated with the production of aluminum through electrolysis?
Which process is associated with the production of aluminum through electrolysis?
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What characterizes oxidation in a redox reaction?
What characterizes oxidation in a redox reaction?
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Which method is used to balance redox reactions by analyzing changes in oxidation numbers?
Which method is used to balance redox reactions by analyzing changes in oxidation numbers?
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What is the primary function of a salt bridge in an electrochemical cell?
What is the primary function of a salt bridge in an electrochemical cell?
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Which of the following describes cell potential?
Which of the following describes cell potential?
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What happens during the reduction process in an electrochemical cell?
What happens during the reduction process in an electrochemical cell?
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How can one determine the feasibility of using a cell to generate an electric current?
How can one determine the feasibility of using a cell to generate an electric current?
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Which type of battery is primarily based on chemical reactions producing immediate electrical energy?
Which type of battery is primarily based on chemical reactions producing immediate electrical energy?
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What is a characteristic of the electrode reactions during electrolysis?
What is a characteristic of the electrode reactions during electrolysis?
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Study Notes
Electrochemistry Overview
- Electrochemistry is the study of the interrelationship between chemical reactions and the electrical energy that accompanies them.
Learning Objectives
- Define oxidation and reduction reactions
- Balance redox reactions using the change in oxidation number method
- Identify the reaction occurring in different parts of the cell
- Define reduction potential, oxidation potential, and cell potential
- Calculate the standard cell potential
- Relate cell potential to the feasibility of generating an electric current
- Describe electrochemistry in common batteries (Leclanche dry cell, button batteries, fuel cells, lead storage)
- Apply electrochemical principles to explain corrosion
- Explain electrode reactions during electrolysis
- Describe reactions in commercial electrolytic processes
Redox Reactions
- Redox reactions involve electron transfer.
- Oxidation is the loss of electrons.
- Reduction is the gain of electrons.
- The combustion of barium metal is a redox reaction (2Ba + O2 → 2BaO).
- The example shows the oxidation and reduction half-reactions in the reaction.
Oxidation Numbers
- Oxidation number indicates the number of electrons lost or gained by an atom in a molecule or ionic compound.
- Atoms in free elements have a zero oxidation number (e.g., He, N2, P4, S8).
- For a monatomic ion, the oxidation number equals the charge of the ion (e.g., Na+, Al3+, Hg₂²⁺, F⁻, S₂⁻).
- Oxygen's oxidation number is typically -2 in compounds, except in OF₂ (where it's +2) or peroxides (where it's -1).
- Hydrogen's oxidation number is +1 in compounds with nonmetals and -1 when bonded to metals.
- Fluorine in compounds has an oxidation number of -1. Other halogens are -1 in halide form but can have positive oxidation numbers when bonded with oxygen or a more electronegative element.
- In a compound, the sum of the oxidation numbers of all atoms is zero; in a polyatomic ion, the sum of the oxidation numbers equals the ion's charge.
Changes in Oxidation Numbers
- A reaction is considered redox when reactant atoms change their oxidation numbers.
- Oxidizing agents are reactants that cause oxidation, and they are reduced in the reaction.
- Reducing agents cause reduction and are oxidized in the reaction.
- A mnemonic to remember is LEORA-GEROA (Loss of Electrons is Oxidation, Reduction is Gain of Electrons, Oxidizing Agent is Reduced, Reducing Agent is Oxidized).
Types of Redox Reactions
- Redox reactions can be observed in combination (e.g., 2Mg + O₂ → 2MgO), decomposition (e.g., 2KClO₃ → 2KCl + 3O₂), combustion (e.g., CH₄ + 2O₂ → CO₂ + 2H₂O), metal displacement (e.g., CuSO₄ + Zn → Cu + ZnSO₄), hydrogen displacement, and halogen displacement reactions.
Balancing Redox Reactions
- Steps for balancing redox reactions involve:
- Write the unbalanced equation.
- Assign oxidation numbers to all elements.
- Draw lines connecting elements involved in oxidation and reduction.
- Determine multipliers that make increases and decreases equal.
- Perform balancing by inspection for other elements.
Electrochemical Cells
- Electrochemical cells create electric current from redox reactions and/or supply electrical energy for the reactions.
- Types include galvanic (voltaic) and electrolytic cells.
Galvanic Cells
- Galvanic cells produce electrical energy from a spontaneous redox reaction.
- Electrodes are surfaces for redox reactions, with the anode being where oxidation takes place and electrons originate and the cathode being where reduction occurs and electrons proceed..
- An anolyte is the solution next to the anode, and the catholyte is next to the cathode.
- Voltmeters are used to measure the potential differences.
- Wires, or external circuits, connect electrodes to a power/battery terminal.
- Salt bridges maintain electrical neutrality in the cell.
Half-Cell Reactions
- An electrochemical cell consists of two half-reactions (anode and cathode). The anode involves oxidation, and the cathode involves reduction.
Overall Cell Reactions
- The overall cell reactions can be determined by adding the anode and cathode half-reactions.
Examples of Galvanic Cells
- The Daniell cell utilizes zinc and copper electrodes immersed in ZnSO4 and CuSO4 solutions, respectively.
- The copper-silver cell uses copper and silver electrodes submerged in CuSO4.and AgNO3 solutions.
Electrode Potentials
- Electrode potential (Ered) represents the potential of reduction.
- Standard reduction potential (Eored), measured under standard conditions, indicates the tendency of a species to be reduced.
- High Eored suggests strong oxidizing potential.
- Conversely, the species with the lowest Eored has the highest reducing capacity.
- Standard cell potential (Eocell) equals the sum of the standard oxidation potential of the anode and the standard reduction potential of the cathode.
- The sign of Eocell determines spontaneity. A positive value indicates a spontaneous reaction.
Batteries
- Batteries are galvanic cells used to provide electrical energy.
- Leclanché
- Button
- Lead Storage
- Nickel-Cadmium
- Lithium-ion
Corrosion
- Corrosion is the process where metals are destroyed by oxidation, frequently in presence of water and oxygen.
- Susceptible sites for rusting on iron (like a nail) are those experiencing mechanical stress.
- Factors hastening rust include electrolytes, acids, and lack of protective coatings (like paint).
###Electrolysis
- Electrolysis is a process that uses an electric current to drive a non-spontaneous redox reaction.
- Electrolytic cells are electrochemical cells used in electrolysis.
- Electrolysis of water decomposes water into hydrogen and oxygen gas.
- Electroplating is an electrolytic coating technique for metals.
- Electrorefining is an electrolytic metal purification process.
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Description
Explore the principles of electrochemistry, focusing on oxidation and reduction reactions, redox balancing, and cell potential calculations. Understand the role of electrochemistry in batteries and corrosion, as well as the reactions involved in electrolytic processes. Gain a comprehensive understanding of how chemical reactions relate to electrical energy.
