Electrode Potential (Nernst)
Calculate the electrode potential by the Nernst equation at 25 °C, E = E° − (0.0592 ÷ n) × log₁₀(Q), from the standard potential E° (V), the number of electrons exchanged n and the reaction quotient Q (ratio of product to reactant activities). The result, in volts, is the actual electrode potential under non-standard conditions — essential to predict the spontaneity of redox reactions, a metal's tendency to corrode in a given medium and the operation of cells, batteries and electrochemical sensors. Enter the standard potential, the number of electrons and the reaction quotient.
Resultado
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Potencial de eletrodo (equação de Nernst)
O potencial padrão E° de um eletrodo vale em condições muito específicas (atividades unitárias, 25 °C, 1 atm). No mundo real as concentrações são outras, e o potencial muda — quem descreve essa dependência é a equação de Nernst. Na forma prática a 25 °C: E = E° − (0,0592 ÷ n) × log₁₀(Q), onde n é o número de elétrons trocados e Q é o quociente reacional (a razão entre as atividades/concentrações dos produtos e dos reagentes, cada uma elevada ao seu coeficiente). O termo 0,0592 V vem de 2,303·RT/F a 298 K. A leitura física é direta: aumentar a concentração de reagentes (Q menor) torna o potencial mais positivo (reação mais favorável); acumular produtos (Q maior) o torna mais negativo, até o equilíbrio (E = 0 na célula). A equação de Nernst é onipresente: prevê a tensão real de pilhas e baterias conforme se descarregam, é a base de funcionamento dos eletrodos seletivos e do pHmetro (cuja leitura é uma medida de potencial), e em corrosão permite construir os diagramas de Pourbaix e avaliar a tendência de um metal a corroer num meio de dada concentração e pH. Informe o potencial padrão, o número de elétrons e o quociente reacional.
Related Tools
Electrochemical Equivalent Weight
Calculate the electrochemical equivalent weight, EW = M ÷ n, dividing the element's molar mass M (g/mol) by the number of electrons exchanged n (valence). The result, in g/eq, is the mass associated with transferring one mole of electrons and appears in nearly every electrochemical calculation: Faraday's law, electrochemical corrosion rate, electrodeposition and anode sizing. For divalent iron (Fe²⁺), for example, EW = 55.85 ÷ 2 ≈ 27.9 g/eq. Enter the molar mass and the number of electrons exchanged.
Tafel Overpotential
Calculate the activation overpotential by the Tafel equation, η = a + b × log₁₀(i), from the Tafel constant a (V), the Tafel slope b (V/decade) and the current density i. The result, in volts, is the overpotential — how far an electrode's potential departs from equilibrium — needed to sustain a given current density in an activation-controlled electrochemical reaction. The Tafel relation is central to electrode kinetics, corrosion (extrapolation to obtain the corrosion current) and electrolysis. Enter the Tafel constant, slope and current density.
Corrosion Inhibitor Efficiency
Calculate the efficiency of a corrosion inhibitor, η = (CR₀ − CR_inh) ÷ CR₀ × 100%, comparing the corrosion rate without inhibitor (CR₀) with the rate in its presence (CR_inh). The result, in %, measures how much the inhibitor slowed corrosion — the standard indicator to evaluate and compare inhibitors in laboratory tests (mass loss, polarization or impedance). Effective inhibitors form protective films on the surface and reach efficiencies above 90%. It is widely used in boiler water treatment, cooling systems and well acidizing. Enter the corrosion rates without and with inhibitor.
Acid Dew Point of Flue Gas
Computes the temperature at which sulphuric acid starts to condense on the cold surfaces of a boiler, using the Verhoff and Banchero correlation: the reciprocal of the absolute dew point temperature is a combination of the logarithms of the partial pressures of water vapour and sulphur trioxide in the flue gas, plus the product of those two logarithms. The result is the thermal floor of the design — keeping the stack, the economiser and the air preheater above it is what prevents the acid corrosion that eats steel in a few weeks, and it is why heavy fuel oil boilers throw away up the stack heat they could otherwise recover. SO₃ is what rules here, not humidity, and the reason is the range each one spans: water vapour barely leaves the 5% to 15% band in a flue gas, which accounts for 11 °C end to end, while SO₃ varies by orders of magnitude with the sulphur in the fuel — going from 1 to 10 ppm alone raises the dew point by almost 22 °C. The Verhoff and Banchero correlation was adopted, with partial pressures in millimetres of mercury at atmospheric pressure, as it is the one most used in boiler design, in its original form with the interaction term between the two logarithms; the later Okkes correlation returns 1 to 8 °C lower for the same composition, so treat the value as a reference and not as an exact limit. Enter the water vapour content and the SO₃ content of the flue gas.
Grain Conical Pile Volume
Calculate the volume of a conical pile of granular material formed by free pouring, V = (π/3)·r³·tan(θ), from the pile base radius r (m) and the material's angle of repose θ (degrees). When granular material is freely poured onto a surface, it naturally forms a CONE whose side slope is the angle of repose — a characteristic property of each material (dry sand ~30-35°, grain ~25-30°, crushed stone ~37-40°) reflecting inter-particle friction. Since the cone height is h = r·tan(θ), the cone volume (1/3·π·r²·h) becomes (π/3)·r³·tan(θ), a function of radius and angle of repose only. This is widely used in practice to estimate, from a survey or base-radius measurement, the volume (and with density, the mass) of open stockpiles — piles of grain, sand, crushed stone, coal, ore, fertilizer in yards and warehouses. It is the basis of bulk-material inventory in piles, a quick alternative to weighing. It also guides stockyard area and height sizing and bulk-warehouse design. For elongated piles (prismatic with conical ends), add the central part. Enter the base radius and the angle of repose.
Overburden-Corrected SPT (N1)60 — Liao and Whitman
Corrects the SPT blow count already normalized to 60% energy for the effect of vertical effective stress, producing the (N1)60 required by liquefaction and relative density correlations. The overburden factor adopted is that of Liao and Whitman (1986), CN = square root of (100 ÷ vertical effective stress) with stress in kilopascal, capped at 1.7; the result is (N1)60 = N60 × CN. The correction exists because the same soil, at the same density, resists penetration more when it is deeper: without it, a loose sand at 20 metres would look denser than the same loose sand at 3 metres, and the liquefaction potential would be underestimated. The reference pressure of 100 kPa (one atmosphere) and the cap of 1.7 recommended by the 1997 NCEER report were adopted, because without a cap the correction blows up at shallow depths; part of the literature uses 95.76 kPa, which is 1 tsf, and a cap of 2.0, changing the result by a few percent. Enter the measured N60 and the vertical effective stress at the test depth.
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