A battery has a voltage, a metal corrodes and a sensor produces a current. These observations can feel like separate topics until electron transfer, ion movement and energy are placed in one account. Electrochemistry provides that account, but it asks us to keep several quantities distinct.
The gold standard of electrochemistry is a balanced chemical explanation connected to a measured electrical response, with the reference, conditions and limitations stated. Voltage, current, charge, reaction amount and useful energy belong together without becoming interchangeable. This root guide develops those connections through original worked cases and links the existing specialist articles by the question each can answer.
The learning aim follows The Gold Standard of Education: learning that transfers into life. You should be able to recognise the same relationship in a changed cell, a different measurement interval or a new application. Numerical cases are invented educational models using rounded constants. They are not specifications for a battery, a plating process or a laboratory procedure.
Find your way through electrochemistry
Follow electron transfer from balanced reactions to voltage, current, measured products and useful devices.
Full chapter index · Practice and explained answers · How X Works
Chapter contents
Balance the cell account · Chapters 1–3
Connect energy, charge and products · Chapters 4–7
Explain working interfaces · Chapters 8–11
Apply and investigate · Chapters 12–14
An oxidation transfers electrons away from a reacting species; a reduction accepts them. A complete redox reaction couples these processes so that electron accounting balances. The half-reaction method makes that account visible without claiming that a free pile of electrons accumulates indefinitely inside an ordinary solution.
For a simple illustrative metal, M → M²⁺ + 2e⁻ represents oxidation. A second process X²⁺ + 2e⁻ → X represents reduction. Adding them gives M + X²⁺ → M²⁺ + X. Electrons cancel because their production and consumption match in the combined reaction.
Now change the second ion to Y³⁺. Matching one M atom with one Y³⁺ does not balance the electron account. Three M atoms release six electrons; two Y³⁺ ions accept six. The combined stoichiometry is therefore 3M + 2Y³⁺ → 3M²⁺ + 2Y. The coefficients carry physical information about amounts.
Oxidation numbers are useful bookkeeping assignments, but they are not always literal measured charges on individual atoms within a bond. Keep formal accounting separate from a detailed electronic-structure claim. The skill is to use the representation for the job it supports.
Before calculating a voltage or product amount, verify atoms and charge in the proposed reaction. An unbalanced equation can produce tidy arithmetic while describing no complete transformation. The error is at the level of the account, not the calculator.
CHAPTER 2 OF 18 · Balance the cell account
2. A cell needs two connected transport paths
A separated electrochemical cell routes electron transfer through an external conductor while ions move within the electrolyte and between relevant regions. Both paths matter. Electrons carried through a wire are not the same objects as ions moving through solution.
If charge could accumulate without limit in one region, it would rapidly alter the electrical conditions. The complete cell therefore needs an internal charge-transport account as well as an external circuit. An electrolyte or separator is part of the mechanism, not an optional accessory added after the interesting chemistry.
A galvanic cell can turn a favourable chemical transformation into electrical work. An electrolytic cell uses supplied electrical work to drive a transformation. The same general redox concepts apply, but electrode signs depend on how the cell is operating.
The enduring definitions are that oxidation occurs at the anode and reduction at the cathode. Memorising that the anode is always negative confuses a common galvanic arrangement with a universal definition. Ask which reaction occurs at each electrode, then determine its role in the actual circuit.
A useful drawing labels the reactions, electron direction in the conductor and relevant ionic motion. It also states the operating mode. If you cannot place those elements consistently, pause before introducing a cell-potential equation. A complete diagram often reveals the hidden misconception more clearly than another verbal definition.
CHAPTER 3 OF 18 · Balance the cell account
3. Electrode potentials are measured relative to a reference
An individual electrode potential is expressed relative to a reference convention. It is not a free-standing absolute voltage that a meter reads without another electrical connection. The reference, conditions and sign convention are part of the reported quantity.
The IUPAC electrode-potential definition and standard-electrode-potential entry provide the terminology. Standard quantities have specified reference conditions; an actual cell need not be operating in those conditions. Temperature also needs to be stated when it matters.
Consider invented standard reduction potentials of +0.40 V for one half-reaction and −0.20 V for another, both on the same reference scale. If the first is reduction at the cathode and the second is reversed for oxidation at the anode, the standard cell potential is +0.40 − (−0.20) = +0.60 V.
Multiplying a half-reaction by a stoichiometric coefficient does not multiply its electrode potential. Potential is energy per unit charge. The total reaction energy changes with the amount of reaction; the potential is not an amount of substance. Confusing these quantities produces a familiar but revealing error.
When comparing tables, first confirm that both values refer to compatible conventions and conditions. A precise difference between incompatible quantities is not a useful cell prediction. The subtraction becomes meaningful only after the references match.
CHAPTER 4 OF 18 · Connect energy, charge and products
4. Voltage connects free energy with transferred charge
For a specified reaction transferring n moles of electrons per mole of reaction, the reversible electrical relation is ΔG = −nFE. F is the Faraday constant, approximately 96,485 coulombs per mole of electrons. A positive reversible cell potential corresponds to a negative Gibbs energy change for the reaction as written under the stated conditions.
Use an original example with n = 2 and E = 0.60 V. The Gibbs energy change is approximately −2 × 96,485 × 0.60 = −115,782 J per mole of reaction, or −116 kJ mol⁻¹. The unit volt means joule per coulomb, so the dimensions explain why charge enters the calculation.
Reverse the reaction and the sign of ΔG reverses. Double the written reaction and its ΔG doubles, while the cell potential remains the same. These two checks separate an extensive energy change from an intensive potential difference.
The relation does not promise that a working device delivers the reversible limit. Current, internal losses and changing composition can reduce the terminal voltage and useful output. A thermodynamic tendency does not guarantee a large rate or an efficient component.
A good explanation therefore states which voltage is being discussed: an equilibrium value, an open-circuit measurement or a terminal value under load. Without that distinction, a statement about energy can silently change from a reversible model into a performance claim the evidence does not establish.
CHAPTER 5 OF 18 · Connect energy, charge and products
5. Composition changes equilibrium voltage
The Nernst equation relates equilibrium potential to reaction composition through the reaction quotient. For a complete cell reaction, E = E° − (RT/nF) ln Q, with activities used in Q. At approximately 298 K, the base-ten form uses about 0.05916/n volts multiplying log₁₀Q.
The IUPAC Nernst-equation entry is the reference for the equilibrium relationship. Activities are dimensionless measures of effective composition relative to standard states. Concentration can be an approximation in suitable circumstances, not an unrestricted replacement in every electrolyte.
In an invented two-electron reaction with E° = 0.60 V and Q = 100, the approximate 298 K potential is 0.60 − (0.05916/2) × 2 = 0.541 V. Increasing Q in this expression reduces the potential for the reaction as written. Reversing the reaction also changes the quotient and sign convention; do not change one while keeping the other frozen.
A concentration cell can generate a potential from unequal chemical conditions even when the electrode material is the same on both sides. The driving difference is in the chemical state, not a requirement that two different metals must always be present.
The equation describes an equilibrium relation. It does not, by itself, predict the full current–voltage curve while a cell is running. Kinetics, transport and resistance enter that next problem. Naming the boundary makes the equation more useful, because it prevents it from being asked to explain an observable outside its job.
CHAPTER 6 OF 18 · Connect energy, charge and products
6. Current becomes amount only after integration
Current is the rate of charge transfer: I = dQ/dt. For constant current, Q = It. When current varies, total charge is the time integral. A large instantaneous current and a long-running moderate current can therefore transfer different total amounts.
Consider a teaching cell operating at 0.40 A for 15 minutes. Convert time to 900 seconds, giving Q = 360 C. Dividing by F gives approximately 0.00373 mol of electrons. If the desired reaction requires two electrons per product unit, the ideal amount is 0.00187 mol of product.
Changing the run to 0.20 A for 30 minutes transfers the same charge in this simple account. It need not give the same practical result: changing current density can alter competing reactions, transport and efficiency. Equal charge is one established equality, not proof that every part of the process is equivalent.
An ampere-hour is a charge unit. One ampere-hour equals 3,600 C. It is not an energy unit until an appropriate voltage account is added. This is why two batteries with equal ampere-hour ratings need not store equal energy.
For a varying current, a graph provides the route: estimate the area under current versus time. Make the intervals and units explicit. A peak current alone cannot determine the total charge, just as a peak speed cannot determine the total distance without a time history.
CHAPTER 7 OF 18 · Connect energy, charge and products
7. Faradaic efficiency tests the product account
The ideal Faraday calculation assumes the counted charge is assigned to the intended reaction. Real cells can support competing reactions, capacitive charging or other contributions. Faradaic efficiency asks what fraction of the relevant charge is accounted for by a specified product pathway.
In an original case, 965 C passes through a cell. That is approximately 0.0100 mol of electrons. A desired two-electron product would ideally reach 0.00500 mol. If independent product analysis finds 0.00400 mol, the charge assigned to it is 2F × 0.00400 ≈ 772 C, giving a faradaic efficiency of about 80%.
The remaining charge is not automatically waste heat, and it does not identify one particular competing reaction. A product balance, gas analysis or another appropriate measurement may be needed. Efficiency names a discrepancy relative to a chosen target; it does not by itself explain the discrepancy.
Now change the product stoichiometry to four electrons per product unit. The same measured product amount corresponds to a different charge. An incorrect reaction coefficient would therefore distort the efficiency even if both the electrical integration and chemical measurement were accurate.
The transferable check is to use two independent accounts: integrated charge and measured product amount. Compare them through balanced stoichiometry. Where they disagree, investigate rather than forcing a perfect yield by assuming that all current must have produced what you hoped to make.
Reconcile two independent product measurements
An original product-balance exercise makes the inference more demanding. A cell passes 1,930 C, approximately 0.0200 mol of electrons. Independent analysis reports 0.00600 mol of a two-electron product A and 0.00200 mol of a four-electron product B. Product A accounts for 0.0120 mol of electrons and B for 0.00800 mol. Together they account for the integrated charge within the rounded teaching data.
| Product | Measured amount | Electrons per product unit | Electron amount accounted for |
|---|---|---|---|
| A | 0.00600 mol | 2 | 0.0120 mol |
| B | 0.00200 mol | 4 | 0.00800 mol |
| Combined | Different products remain distinct | Not a shared coefficient | 0.0200 mol |
Adding the product amounts first and dividing charge by a single coefficient would erase their different stoichiometries. The electron account lets the two measurements be compared while keeping the products chemically distinct. This is the same reason that adding quantities with different meanings cannot be repaired by a final unit label.
Now suppose a revised analysis reports only 0.00100 mol of B. The products would account for 0.0160 mol of electrons, or 80% of the approximate total. That remaining difference could reflect another pathway, incomplete product recovery, analytical bias or charging contributions. It is a discrepancy to investigate, not permission to invent a missing product.
A complete investigation would record analytical uncertainty and explain whether products were measured where they formed or after collection and possible loss. Perfect charge closure can also be misleading if measurements share a common calibration error or an incorrect stoichiometric assumption. Independent evidence needs independent failure modes where possible.
The practical learning task is reconciliation. Preserve each quantity’s identity, convert through a justified relationship and identify what remains unexplained. A balance that does not close honestly is more informative than a perfect-looking total assembled from incompatible measurements.
CHAPTER 8 OF 18 · Explain working interfaces
8. Reaction speed and driving force are different
A reaction can be thermodynamically favourable yet proceed slowly. Electron transfer at an interface has kinetics, and the available surface, reaction pathway and environment matter. The potential needed to sustain a useful current can differ from the equilibrium value.
Overpotential describes an electrode’s displacement from its equilibrium potential under the relevant conditions. It helps organise kinetic departures from equilibrium, but it is not the only voltage loss in a complete cell. Resistance in the electrolyte and connections can also contribute to the measured difference.
Imagine a fictional cell whose reversible voltage is 1.00 V but whose terminal voltage during discharge is 0.80 V at 0.50 A. The delivered electrical power is 0.40 W. The difference from the reversible ideal signals losses or departures that require an account; it does not isolate their cause without further measurements.
Increasing surface area can reduce current per unit active area for a fixed total current, but area itself needs definition. Geometric area, roughness and electrochemically active area are not always the same. Comparing two electrodes using an unexplained denominator can misrepresent their apparent performance.
A useful explanation separates equilibrium, kinetics and resistance before combining them. Each has its own evidence. A single terminal-voltage curve may be compatible with several combinations, so the next experiment should be chosen to distinguish those possibilities rather than merely repeat the same measurement more neatly.
CHAPTER 9 OF 18 · Explain working interfaces
9. Mass transport sets another boundary
Reactants must reach an active interface and products must leave or be accommodated. Diffusion, migration in an electric field and convection can all contribute. A fast interfacial reaction can become limited by the supply of material rather than by electron-transfer kinetics.
Suppose an invented interface can consume a reactant faster than diffusion replenishes it. Raising the driving potential further may produce little increase in the desired current once supply is limiting. The plateau does not demonstrate that nothing is changing; it indicates a boundary in the model of delivery to the surface.
Changing stirring, geometry or concentration can test a transport explanation. Such changes can also alter other conditions, so state what was controlled. A persuasive interpretation predicts how the response should depend on the changed transport condition before the result is known.
This is why a tiny laboratory electrode and a large industrial electrode do not automatically behave alike at the same applied voltage. Distances, flow, resistance and surface distribution can change. Scaling total current by area alone may omit the transport conditions that supported the original result.
The useful life connection is broader than electrochemistry: increasing a process’s intrinsic capability does not always increase its output if delivery becomes the bottleneck. Here that analogy becomes a physical question about concentration near an interface, flux and an experimentally testable current limit. The mechanism, rather than the slogan, should finish the explanation.
CHAPTER 10 OF 18 · Explain working interfaces
10. Interfaces can store charge without making product
At an electrode–electrolyte interface, charge distribution can change as potential changes. This interfacial charging contributes current even without the same net chemical transformation used in a faradaic product calculation. It is one reason current cannot always be equated directly with reaction rate.
A simple capacitor model writes Q = CΔV. If an invented interface has capacitance 200 microfarads and its potential changes by 0.50 V, the idealised stored charge change is 100 microcoulombs. That number follows from the model; it does not establish that a particular amount of a chemical product was formed.
The model’s assumptions need attention. A real interface may have potential-dependent capacitance, roughness, adsorption and distributed response. Calling every interfacial feature a perfect capacitor can hide the physical question rather than answer it.
Electrochemical impedance measurements examine response across frequency. Different processes can dominate at different timescales, but an equivalent circuit is an interpretive model. Several circuits may fit a limited dataset. The physical meaning of each element needs supporting evidence and a relevant measurement range.
The existing impedance article offers a focused next route. Before following it, keep the foundational distinction clear: a current transient may contain charging and reaction contributions. Integrating all of it and dividing by an electron coefficient can produce a product estimate that no independent chemical measurement supports.
CHAPTER 11 OF 18 · Explain working interfaces
11. Batteries combine quantities with different meanings
Battery discussions often mix voltage, capacity, energy, power, state of charge and state of health. These are connected but distinct. Capacity is an amount of transferable charge under stated conditions. Energy involves voltage throughout the transfer. Power is an instantaneous rate of energy delivery.
For a fictional cell delivering 2.0 Ah at an approximately constant 3.0 V, the simplified energy is 6.0 Wh. If another cell delivers the same charge at 1.5 V, the corresponding estimate is 3.0 Wh. Equal ampere-hours do not make equal energy. If voltage changes substantially, integrate voltage with transferred charge rather than multiply by an arbitrary endpoint.
State of charge describes a position within a defined usable charge range. State of health describes deterioration relative to an appropriate reference, potentially including capacity and resistance. A display reading 100% does not by itself establish that an aged cell has its original capacity.
Charging and discharging conditions influence what is measured. Temperature, rate, cut-off rules and prior history can change the usable result. A comparison should therefore preserve the test conditions instead of treating the number printed beside capacity as independent of method.
The existing battery mathematics guide and battery-manufacturing Gold Standard article extend these distinctions. The scientific root explains the quantities; engineering adds design, operation, quality and recovery questions. A useful bridge keeps both jobs visible without treating a simple classroom cell as a complete product qualification.
Corrosion can involve anodic metal dissolution coupled with a cathodic reaction elsewhere on the same object or system. The regions need not be separate objects joined by a visibly labelled wire. Local conditions, electrical connections and ionic paths can support the coupled process.
A coating may protect by separating the surface from an environment, but defects, edges and interfaces matter. A protective strategy must be interpreted in its actual material and exposure conditions. Saying that one metal is always protected by another ignores the electrochemical and geometric context.
In a hypothetical comparison, the same total corrosion current is concentrated over a small exposed defect in one sample and spread over a much larger area in another. Average current over the whole object can conceal very different local damage rates. The denominator matters because local material loss may determine failure.
This is a useful changed-context test of the electrode-area discussion. More total area is not automatically more local harm, and a low average over a large structure may conceal a concentrated problem. A proper investigation asks where the current and damage occur.
The existing corrosion guide connects this physical explanation with infrastructure care. This article does not prescribe a protection system for a particular structure. It gives the reader a question worth carrying into a professional account: which coupled reactions, pathways and local conditions explain the observed deterioration, and what evidence would distinguish them from alternatives?
CHAPTER 13 OF 18 · Apply and investigate
13. Sensors and voltammetry turn responses into inferences
An electrochemical sensor uses a measured potential, current or another electrical response to infer something about a chemical system. Its interpretation requires selectivity, calibration and attention to the sample matrix. A response to a standard solution does not automatically establish the same response in every real sample.
In cyclic voltammetry, potential is swept and current recorded. Peaks and their changes can reveal information about redox processes and transport, but a peak is not a self-interpreting chemical label. Scan rate, electrode condition, reference stability and solution resistance can influence the result.
Consider a fictional sensor calibrated with a straight-line response over a specified concentration range. An unknown gives a signal outside that range. Extending the line may produce a number, but the calibration did not establish that extrapolation. Dilution, a revised method or an appropriately validated range would be a more defensible next step.
A blank and a standard answer different questions. The blank helps examine background response; the standard tests response to a known reference under its conditions. Neither alone establishes that other sample constituents do not interfere. A useful measurement plan keeps these jobs separate.
The linked voltammetry and analytical-chemistry guides develop those questions. The general skill is to preserve the inference chain: chemical state, interaction with the electrode, instrument response, calibration and reported quantity. Whenever one link changes, ask whether the earlier calibration still applies.
CHAPTER 14 OF 18 · Apply and investigate
14. Learn the subject through a sequence of checks
Begin with balanced reactions and units. Then distinguish voltage from current and charge. Add equilibrium potentials before asking why a working cell departs from them. Introduce kinetics, transport and interfacial charging as separate explanatory needs. This sequence reduces the temptation to use one equation for every electrical observation.
A teacher can diagnose difficulty by asking for two accounts of the same case. Can the student balance the electron transfer? Can they explain how measured charge becomes product amount? If the coefficients are correct but minutes are left as seconds, the repair is a unit habit. If the units are correct but all current is assigned to one product without justification, the repair concerns the measurement model.
Practice should change conditions deliberately. First calculate ideal product under constant current. Next vary the current over two intervals. Then provide an independently measured yield and ask for faradaic efficiency. Finally introduce a charging transient and ask which part of the earlier interpretation now needs evidence.
Professional electrochemistry adds supervised experimental skill, instrument knowledge, chemical competence and reproducible records. A career may involve materials, sensors, energy, corrosion, analysis or industrial processes. These roles share principles but not identical daily tasks.
A useful study notebook records the reaction, reference, electrical quantity, chemical quantity and main assumption for every worked example. That small discipline makes later complexity navigable. You can return to the exact relationship that became unstable instead of deciding that you are simply weak at electrochemistry.
CHAPTER 15 OF 18 · Check and explore
15. Questions that expose common misconceptions
Does a high open-circuit voltage prove a powerful battery?
No. Open-circuit voltage does not establish the current a cell can sustain under load, its usable charge or its energy over discharge. Power and energy need additional measurements and conditions.
Are anode and cathode defined by their signs?
They are defined by reaction: oxidation at the anode, reduction at the cathode. Electrode signs depend on operating mode. Track the reactions first and determine the electrical arrangement from the actual cell.
Why do electrode potentials not multiply with coefficients?
Potential is energy per charge. Multiplying a reaction increases both reaction energy and transferred charge by the same factor. Their ratio does not multiply. Gibbs energy and stoichiometry keep the account consistent.
Does all current form the desired product?
Not necessarily. Competing reactions and charging can contribute. Use independent product analysis and the correct electron coefficient before interpreting efficiency or yield.
Is a fitted equivalent circuit a unique mechanism?
Not automatically. A fit establishes compatibility within a model and dataset. Independent observations, physically meaningful parameters and a suitable frequency range help test the interpretation.
Does a standard potential predict every practical cell voltage?
No. Actual composition, temperature, reference conventions, resistance and current-dependent departures can matter. Identify which potential was calculated and which voltage was measured.
These questions are useful because they locate a hidden change of quantity. Repair that change before adding more formulae. A shorter calculation with the right physical account is more valuable than a long one whose central variable has shifted meaning.
CHAPTER 16 OF 18 · Check and explore
16. Practice and explained changed-context answers
First, a fictional reaction transfers three electrons per product unit. A constant 0.30 A flows for 20 minutes. Charge is 360 C, electron amount is approximately 0.00373 mol and ideal product amount is approximately 0.00124 mol. If product analysis gives 0.000995 mol, the inferred faradaic efficiency is about 80% under the stated account.
Second, current is 0.50 A for 100 seconds and 0.20 A for 200 seconds. Total charge is 50 + 40 = 90 C. Averaging the two currents without weighting their durations would give the wrong answer. The graph’s area, rather than the unweighted mean of two labels, preserves the quantity.
Third, an invented standard cell has reduction potentials +0.25 V and −0.35 V on a common scale. Using the more positive one as the cathode gives E° = +0.60 V. Doubling the overall balanced reaction leaves 0.60 V unchanged while doubling its Gibbs energy change per written reaction amount.
Fourth, a cell has two electrons in its balanced reaction, E° = 0.50 V and Q = 0.01 at approximately 298 K. Since log₁₀Q = −2, the Nernst estimate is 0.559 V. The direction check matters: smaller Q favours the forward reaction more strongly in this formulation.
Finally, two cells transfer the same charge, but one operates at half the voltage throughout. Its idealised electrical energy transfer is half as large. Explain why equal ampere-hours establish charge equality, not energy equality. A good answer names the additional voltage history needed when the voltage is not constant.
CHAPTER 17 OF 18 · Check and explore
17. Connected reading by the next physical question
Foundations and the main mechanism
Electrochemistry mechanism guide develops electron transfer, potential, current and cells. The Gold Standard of Physical Chemistry connects equilibrium, energy and kinetics. The Gold Standard of Inorganic Chemistry develops ions, metals and their reactions. The Gold Standard of Analytical Chemistry follows calibration and chemical evidence.
Measure a reaction or interface
Cyclic voltammetry examines potential sweeps and current response. Electrochemical impedance spectroscopy explores frequency and interfaces. Electrochromic windows connects redox with optical change. Analytical chemistry mechanisms provides further measurement and separation context. Chemical energetics and calorimetry offers a distinct way to investigate energy changes.
Carry the account into applications
Batteries, charge, capacity and degradation develops the mathematical distinctions. Corrosion, coatings and infrastructure care examines coupled reactions in use. The Gold Standard of Electrochemical Engineering connects useful reactions with integrated systems. The Gold Standard of Battery Manufacturing Companies adds cell and pack quality, traceability and recovery questions. These application guides extend the scientific account rather than replace its reaction and measurement foundations.
Practise the relationships
Electrolysis, Faraday's law and electrodes gives a focused study route. Electrochemistry and redox calculations connects reaction balance with quantitative work. Electrolysis, electrode products and redox literacy revisits the foundational reasoning. Metal reactivity, rusting and protection connects reaction tendencies with practical interpretation. The Gold Standard of Education and How X Works return to the wider learning network.
CHAPTER 18 OF 18 · Check and explore
18. Primary sources, limits and your next step
The IUPAC entries for electrode potential, standard electrode potential, formal electrode potential and the Nernst equation were checked on 21 October 2026 for definitions and equilibrium terminology. A formal potential refers to specified conditions and conventions; it should not be silently interchanged with a standard potential.
The rounded physical constants can be checked against the NIST 2022 CODATA complete listing, including the Faraday constant, elementary charge and atomic-mass energy equivalent as relevant to the calculation.
The numerical cases in this article are original teaching examples. Reaction potentials, concentrations, currents and yields were chosen to expose particular relationships. Rounded constants and idealised assumptions keep the reasoning visible. They do not describe a verified commercial cell, a real production yield or a recommended experimental setup. The specialist ecosystem guides provide further references for their individual methods and applications.
For a final check, explain a battery measurement using five different nouns: voltage, current, charge, reaction amount and energy. Say how each connects to the next, and identify one reason a real device can depart from the ideal account. If the explanation becomes circular, return to the earliest quantity whose meaning is unclear.
Electrochemistry becomes easier to reason about when the pathways and quantities stay visible. Its gold standard is a chemical and electrical account that another person can follow, test and adapt when the conditions change.