Redox reactions
54 flashcards covering Redox reactions for the MCAT Chem / Phys / Psych / Soc section.
Redox reactions, also known as reduction-oxidation reactions, involve the transfer of electrons between chemical species. In simple terms, one substance loses electrons (oxidation) while another gains them (reduction), resulting in a change in the oxidation states of the atoms involved. This process is essential in many natural and industrial contexts, such as energy production in batteries, corrosion of metals, and metabolic pathways in living organisms.
On the MCAT, redox reactions appear primarily in the Chemical and Physical Foundations section, often as multiple-choice questions testing your ability to balance equations, identify oxidizing and reducing agents, or apply concepts to electrochemical cells and biological systems. Common traps include miscalculating oxidation numbers or confusing oxidation with reduction, so focus on practicing half-reactions and understanding electron flow in real-world scenarios like photosynthesis or respiration to handle these effectively.
A concrete tip: Always start by assigning oxidation numbers to track electron changes accurately.
Terms (54)
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Oxidation
Oxidation is the process in which a substance loses electrons, often accompanied by 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 substance gains electrons, often accompanied by a decrease in oxidation state, and occurs alongside oxidation in redox reactions.
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Redox reaction
A redox reaction is a chemical process involving the transfer of electrons between species, where one undergoes oxidation and another undergoes reduction.
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Oxidizing agent
An oxidizing agent is the substance that accepts electrons in a redox reaction, thereby causing another substance to be oxidized and getting reduced itself.
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Reducing agent
A reducing agent is the substance that donates electrons in a redox reaction, thereby causing another substance to be reduced and getting oxidized itself.
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Oxidation state
Oxidation state is a hypothetical charge assigned to an atom in a molecule or ion, based on rules like assigning electrons to the more electronegative atom, to track electron transfer in redox reactions.
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Half-reaction
A half-reaction is an equation that represents either the oxidation or reduction process in a redox reaction, showing the electron loss or gain for one species.
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Balancing redox reactions
Balancing redox reactions involves using the half-reaction method to ensure that the number of electrons lost in oxidation equals those gained in reduction, often in acidic or basic conditions.
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Galvanic cell
A galvanic cell is an electrochemical cell that converts chemical energy into electrical energy through spontaneous redox reactions, with oxidation at the anode and reduction at the cathode.
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Electrolytic cell
An electrolytic cell uses electrical energy to drive a non-spontaneous redox reaction, with oxidation occurring at the anode and reduction at the cathode.
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Anode
The anode is the electrode in an electrochemical cell where oxidation occurs, releasing electrons that flow through the external circuit.
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Cathode
The cathode is the electrode in an electrochemical cell where reduction occurs, accepting electrons from the external circuit.
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Standard hydrogen electrode
The standard hydrogen electrode is a reference electrode with a potential of zero volts, used as a baseline to measure the standard reduction potentials of other half-cells.
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Standard reduction potential
Standard reduction potential is the voltage associated with a reduction half-reaction under standard conditions of 1 M concentration, 1 atm pressure, and 25°C, indicating the tendency to gain electrons.
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Nernst equation
The Nernst equation calculates the cell potential under non-standard conditions, given by E = E° - (RT/nF) ln Q, where E is the cell potential, E° is the standard potential, R is the gas constant, T is temperature, n is the number of moles of electrons, F is Faraday's constant, and Q is the reaction quotient.
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Electrochemical series
The electrochemical series is a list of elements arranged by their standard reduction potentials, helping predict the spontaneity of redox reactions based on which species is more likely to be reduced.
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Faraday's first law
Faraday's first law states that the amount of substance altered at an electrode during electrolysis 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 the mass of different substances liberated by the same quantity of electricity is proportional to their equivalent weights, which relate to their molar masses and the number of electrons involved in the reaction.
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Electrolysis
Electrolysis is a process using an electric current to drive a non-spontaneous redox reaction, commonly used to decompose compounds or plate metals.
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Corrosion
Corrosion is a redox process, such as the rusting of iron, where the metal oxidizes in the presence of oxygen and water, leading to deterioration.
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Combustion reaction
A combustion reaction is a rapid redox process where a substance reacts with oxygen, producing heat and light, such as the burning of hydrocarbons to form carbon dioxide and water.
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Disproportionation reaction
A disproportionation reaction is a redox process in which a single species is both oxidized and reduced, like the reaction of chlorine with water to form hypochlorous acid and hydrochloric acid.
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Single displacement reaction
A single displacement reaction is a redox process where one element replaces another in a compound, such as zinc displacing copper in copper sulfate solution.
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Combination reaction
A combination reaction is a redox process where two or more substances combine to form a single product, like the reaction of sodium and chlorine to form sodium chloride.
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Decomposition reaction
A decomposition reaction is a redox process where a compound breaks down into simpler substances, often requiring energy, such as the electrolysis of water into hydrogen and oxygen.
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Battery
A battery is a portable electrochemical cell or group of cells that produces electricity from spontaneous redox reactions, commonly used in devices for energy storage.
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Fuel cell
A fuel cell is an electrochemical device that converts the chemical energy of a fuel, like hydrogen, and an oxidizing agent, like oxygen, directly into electrical energy through redox reactions.
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pH dependence in redox
pH dependence in redox reactions refers to how the potential of a half-reaction changes with hydrogen ion concentration, as seen in reactions involving H+ ions, affecting cell voltage.
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Overpotential
Overpotential is the extra voltage required beyond the theoretical value to drive an electrochemical reaction at a desired rate, due to kinetic barriers in redox processes.
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Gibbs free energy and redox
Gibbs free energy relates to redox reactions through the equation ΔG = -nFE, where a negative ΔG indicates a spontaneous reaction, linking thermodynamics to electrochemical potential.
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Spontaneity of redox reactions
The spontaneity of redox reactions is determined by the sign of the cell potential; if E > 0, the reaction is spontaneous, as it corresponds to a positive ΔG value.
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Equilibrium constant for redox
The equilibrium constant for a redox reaction can be calculated from the standard cell potential using K = e^(nFE°/RT), indicating the extent of the reaction at equilibrium.
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Concentration cell
A concentration cell is an electrochemical cell where the same species are at the electrodes but at different concentrations, generating voltage from the difference in redox potentials.
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Salt bridge
A salt bridge is a tube containing an electrolyte that connects the two half-cells in an electrochemical setup, maintaining electrical neutrality by allowing ion flow.
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Electron flow in cells
In electrochemical cells, electrons flow from the anode, where oxidation occurs, through the external circuit to the cathode, where reduction takes place, driving electrical current.
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Ion migration
Ion migration in electrochemical cells involves cations moving toward the cathode and anions toward the anode through the electrolyte, balancing the charge as electrons move externally.
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Electrode potential
Electrode potential is the measure of the tendency of a half-cell to gain or lose electrons, determined relative to a standard reference electrode in redox systems.
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Cell potential
Cell potential is the difference in electrode potentials between the two half-cells in an electrochemical setup, indicating the driving force for the redox reaction.
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Calculating cell voltage
Calculating cell voltage involves subtracting the reduction potential of the anode from that of the cathode, using Ecell = Ecathode - Eanode, to determine if the reaction is spontaneous.
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Example: Zinc-copper cell
In a zinc-copper galvanic cell, zinc is oxidized at the anode (Zn → Zn2+ + 2e-), and copper is reduced at the cathode (Cu2+ + 2e- → Cu), producing a cell potential of about 1.10 volts.
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Rusting of iron
Rusting of iron is a redox process where iron oxidizes in the presence of oxygen and water to form iron(III) oxide, accelerated by electrolytes like salt.
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Bleaching with chlorine
Bleaching with chlorine involves a redox reaction where chlorine acts as an oxidizing agent, accepting electrons from colored compounds and breaking their chromophores.
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Electron transport chain
The electron transport chain is a series of redox reactions in mitochondria that transfer electrons from donors like NADH to acceptors like oxygen, driving ATP synthesis.
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Photosynthesis redox
In photosynthesis, redox reactions split water molecules, oxidizing them to produce oxygen and reducing carbon dioxide to glucose, powered by light energy.
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Respiration redox
Cellular respiration involves redox reactions where glucose is oxidized and oxygen is reduced, releasing energy stored in ATP through processes like glycolysis and the Krebs cycle.
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Redox titration
A redox titration determines the concentration of an analyte by adding a titrant that reacts in a redox process, with the endpoint detected by a color change or electrode.
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Iodometric titration
Iodometric titration is a redox method using iodine as a titrant to quantify oxidizing agents, where the reaction involves the reduction of iodine to iodide ions.
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Redox indicators
Redox indicators are substances that change color at a specific oxidation-reduction potential, used to detect the endpoint in titrations involving electron transfer.
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Potentiometric titration
Potentiometric titration monitors the cell potential during a redox reaction to determine the equivalence point, using a voltmeter instead of an indicator.
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Strategy for identifying redox reactions
To identify redox reactions, compare the oxidation states of elements before and after the reaction; if any increase or decrease, electron transfer has occurred.
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Common traps in balancing redox
A common trap in balancing redox reactions is forgetting to balance oxygen and hydrogen in acidic or basic solutions using water and H+ or OH- ions, leading to incorrect equations.
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Effect of concentration on redox
The effect of concentration on redox reactions is described by Le Chatelier's principle, where changing reactant or product concentrations shifts the equilibrium and alters the cell potential.
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Temperature effects on redox
Temperature affects redox reactions by influencing the rate and equilibrium, as seen in the Nernst equation, where higher temperatures can increase reaction speed but alter potentials.
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Catalysts in redox reactions
Catalysts in redox reactions lower the activation energy without being consumed, speeding up processes like those in the electron transport chain.