Electrochemistry
53 flashcards covering Electrochemistry for the MCAT Chem / Phys / Psych / Soc section.
Electrochemistry is the study of how chemical reactions produce or are driven by electricity. At its core, it involves the transfer of electrons between substances, as seen in batteries that convert chemical energy into electrical power or in electrolysis, where an electric current splits compounds like water into hydrogen and oxygen. This topic bridges chemistry and physics, helping us understand energy transformations in everyday applications, from powering devices to industrial processes like metal refining.
On the MCAT, electrochemistry features in the Chemical and Physical Foundations section, often through questions on redox reactions, electrochemical cells, and the Nernst equation. Expect multiple-choice problems that test balancing half-reactions, calculating cell potentials, or predicting reaction spontaneity. Common pitfalls include confusing oxidation with reduction or overlooking concentration effects in non-standard conditions, so focus on practicing problem-solving with real-world scenarios. For mastery, always double-check the direction of electron flow in cells.
Terms (53)
- 01
Oxidation
Oxidation is the process in which a species loses electrons, often involving an increase in oxidation state, and is a key part of redox reactions.
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Reduction
Reduction is the process in which a species gains electrons, typically resulting in a decrease in oxidation state, and occurs alongside oxidation in redox reactions.
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Oxidation state
The oxidation state is a hypothetical charge assigned to an atom in a molecule or ion, based on rules that help track electron transfer in redox processes.
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Redox reaction
A redox reaction is a chemical reaction that involves the transfer of electrons between species, with one undergoing oxidation and the other reduction.
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Oxidizing agent
An oxidizing agent is a substance that accepts electrons from another species, thereby causing oxidation and getting reduced itself in the process.
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Reducing agent
A reducing agent is a substance that donates electrons to another species, causing reduction and getting oxidized itself during the reaction.
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Anode
The anode is the electrode in an electrochemical cell where oxidation occurs, meaning electrons are released into the external circuit.
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Cathode
The cathode is the electrode in an electrochemical cell where reduction occurs, meaning electrons are gained from the external circuit.
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Galvanic cell
A galvanic cell is an electrochemical cell that converts chemical energy into electrical energy through spontaneous redox reactions.
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Electrolytic cell
An electrolytic cell is an electrochemical cell that uses electrical energy to drive non-spontaneous redox reactions.
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Half-reaction
A half-reaction is an equation that represents either the oxidation or reduction part of a redox reaction, showing electron loss or gain.
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Standard reduction potential
Standard reduction potential is the measure of the tendency of a chemical species to be reduced, measured in volts under standard conditions relative to the hydrogen electrode.
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Cell potential
Cell potential is the voltage difference between the two electrodes in an electrochemical cell, which determines the spontaneity of the reaction.
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Nernst equation
The Nernst equation calculates the cell potential under non-standard conditions, relating it to the standard cell potential and the concentrations of reactants and products.
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Faraday's law of electrolysis
Faraday's law of electrolysis states that the amount of substance produced at an electrode is proportional to the quantity of electricity passed through the cell.
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Electrolysis
Electrolysis is a process that uses an electric current to drive a non-spontaneous chemical reaction, often to decompose compounds into their elements.
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Salt bridge
A salt bridge is a component in an electrochemical cell that allows ions to flow between the two half-cells, maintaining electrical neutrality.
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Electrode
An electrode is a conductor through which electrons enter or leave an electrochemical cell, serving as the site for oxidation or reduction.
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Standard hydrogen electrode
The standard hydrogen electrode is a reference electrode with a potential defined as zero volts, used to measure the potentials of other electrodes.
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Gibbs free energy in electrochemistry
In electrochemistry, Gibbs free energy relates to cell potential, where a negative change indicates a spontaneous reaction and is calculated as ΔG = -nFE.
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Relationship between E and ΔG
The relationship between cell potential E and Gibbs free energy ΔG is given by ΔG = -nFE, where n is the number of moles of electrons and F is the Faraday constant.
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Equilibrium constant from E°
The equilibrium constant K can be derived from the standard cell potential E° using the equation log K = nE° / (0.0592 at 25°C), linking thermodynamics and electrochemistry.
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Concentration cell
A concentration cell is an electrochemical cell where the electrodes are the same material but differ in ion concentration, generating voltage from concentration differences.
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pH and electrode potential
pH affects electrode potential in reactions involving H+ ions, as seen in the Nernst equation, where changes in acidity can shift the cell potential.
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Corrosion
Corrosion is the electrochemical process by which metals degrade due to oxidation, often accelerated by environmental factors like moisture and oxygen.
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Battery
A battery is a portable electrochemical cell or group of cells that converts chemical energy into electrical energy through redox reactions.
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Fuel cell
A fuel cell is an electrochemical device that generates electricity from the reaction of a fuel, like hydrogen, with an oxidant, producing water as a byproduct.
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Electroplating
Electroplating is an electrolytic process that deposits a layer of metal onto an object by using it as the cathode in a solution containing metal ions.
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Faraday constant
The Faraday constant is the charge of one mole of electrons, approximately 96,485 coulombs per mole, used in calculations for electrolysis and cell potentials.
- 30
Ampere-hour
Ampere-hour is a unit of electric charge equal to the charge transferred by a current of one ampere flowing for one hour, useful in electrolysis quantity calculations.
- 31
Overvoltage
Overvoltage is the extra voltage required beyond the theoretical value to drive an electrochemical reaction, often due to kinetic barriers at the electrode.
- 32
Polarization in electrochemistry
Polarization refers to the deviation of electrode potential from its equilibrium value due to the current flow, affecting the efficiency of electrochemical cells.
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Electrolyte
An electrolyte is a substance that conducts electricity when dissolved in water or melted, by dissociating into ions that carry the current.
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Non-spontaneous reaction
A non-spontaneous reaction in electrochemistry has a positive Gibbs free energy change and requires external energy, as in electrolytic cells.
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Spontaneous reaction
A spontaneous reaction has a negative Gibbs free energy change and occurs naturally, powering galvanic cells to produce electricity.
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Half-cell potential
Half-cell potential is the potential of a single electrode relative to a standard reference, which combines to give the overall cell potential.
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Cell diagram
A cell diagram is a shorthand notation that represents the components of an electrochemical cell, showing electrodes, phases, and the direction of electron flow.
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Balancing redox equations in acidic solution
Balancing redox equations in acidic solution involves using H+ and H2O to balance atoms and charges, ensuring the reaction is stoichiometrically correct.
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Balancing redox equations in basic solution
Balancing redox equations in basic solution requires adding OH- and H2O as needed, after initially balancing as if in acidic conditions.
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Common oxidizing agents
Common oxidizing agents include oxygen, chlorine, and permanganate ions, which readily accept electrons in redox reactions.
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Common reducing agents
Common reducing agents include hydrogen gas, sodium borohydride, and metals like zinc, which donate electrons in redox processes.
- 42
Zinc-copper cell
The zinc-copper cell is a galvanic cell where zinc is oxidized at the anode and copper ions are reduced at the cathode, producing a measurable voltage.
In this cell, zinc electrode contacts ZnSO4 solution, and copper electrode contacts CuSO4 solution, connected by a salt bridge.
- 43
Electrolysis of water
Electrolysis of water decomposes it into hydrogen and oxygen gases using an electric current, with reactions occurring at separate electrodes.
At the cathode, 2H2O + 2e- → H2 + 2OH-, and at the anode, 2H2O → O2 + 4H+ + 4e-.
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Calculation of cell voltage
Calculation of cell voltage involves subtracting the reduction potential of the anode from that of the cathode, using standard or adjusted values.
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Effect of concentration on cell potential
The effect of concentration on cell potential is described by the Nernst equation, where increasing reactant concentration increases the potential.
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Temperature dependence of cell potential
Temperature dependence of cell potential is accounted for in the Nernst equation, where higher temperatures can alter the reaction quotient and thus the voltage.
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Standard conditions for electrochemistry
Standard conditions for electrochemistry include 1 M concentrations, 1 atm pressure, and 25°C, used to define standard reduction potentials.
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Reference electrode
A reference electrode provides a stable potential against which other electrodes are measured, such as the standard hydrogen electrode.
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Indicator electrode
An indicator electrode responds to changes in the concentration of a specific ion, used in potentiometric measurements to monitor reactions.
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Faraday's first law
Faraday's first law states that the mass of a substance altered at an electrode is directly proportional to the quantity of electricity passed through the cell.
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Faraday's second law
Faraday's second law states that for a given quantity of electricity, the mass of an element produced is proportional to its equivalent weight.
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Conductance
Conductance is the measure of an electrolyte's ability to conduct electricity, inversely related to resistance and dependent on ion concentration.
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Overpotential
Overpotential is the difference between the actual voltage required for an electrochemical reaction and its theoretical value, due to kinetic factors.