Schwan Equation
Schwan Equation - Related Videos
03:10
Chemical Equations
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2020
Chemical equations represent the identities and relative quantities of substances involved in a chemical reaction. The substances undergoing reaction are called reactants, and their formulas are placed on the left side of the equation. The substances generated by the reaction are called products, and their formulas are placed on the right side of the equation. Plus signs (+) separate individual reactant and product formulas, and an arrow (→) separates the reactant and product (left and right)...
02:55
Thermochemical Equations
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2020
For a chemical reaction (the system) carried out at constant pressure – with the only work done caused by expansion or contraction – the enthalpy of reaction (also called the heat of reaction, ΔHrxn) is equal to the heat exchanged with the surroundings (qp). The change in enthalpy is an extensive property, and it depends on the amounts of the reactants participating in the reaction (or the number of moles of reactants). The change in enthalpy is specific to the reaction, and the physical...
02:59
The Nernst Equation
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2020
Nonstandard Reaction Conditions The interconnection between standard cell potentials and various thermodynamic parameters such as the standard free energy change ΔG° and equilibrium constant K has been previously explored. For example, a redox reaction involving zinc(II) and tin(II) ions at 1 M concentration with Eºcell = +0.291 V and ΔG° = −56.2 kJ is spontaneous. Discharge of this cell, however, results in a change in the reactant concentration and a steady decrease of the cell potential. At...
02:48
Henderson-Hasselbalch Equation
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2020
The ionization-constant expression for a solution of a weak acid can be written as: Rearranging to solve for [H3O+] yields: Taking the negative logarithm of both sides of this equation gives which can be written as where pKa is the negative of the logarithm of the ionization constant of the weak acid (pKa = −log Ka). This equation relates the pH, the ionization constant of a weak acid, and the concentrations of the weak conjugate acid-base pair in a buffered solution. Scientists often use...
02:35
Clausius-Clapeyron Equation
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2020
The equilibrium between a liquid and its vapor depends on the temperature of the system; a rise in temperature causes a corresponding rise in the vapor pressure of its liquid. The Clausius-Clapeyron equation gives the quantitative relation between a substance’s vapor pressure (P) and its temperature (T); it predicts the rate at which vapor pressure increases per unit increase in temperature. where ΔHvap is the enthalpy of vaporization for the liquid, R is the gas constant, and A is a constant...
FAQs
Predicted voltage changes with several experimental inputs: stronger external fields and larger cell radii alter the estimate, while membrane properties, exposure time, and the cell’s position relative to the field also contribute. Considering these variables together lets researchers relate a specified electrical exposure to the voltage expected across the membrane.
Membrane charging makes the predicted voltage time-dependent rather than instantaneous. The associated time constant describes how charging develops during exposure, so the same field can produce different membrane-voltage estimates at different times. Including this temporal behavior helps researchers identify when the membrane may reach a critical voltage during an electrical treatment.
The model assumes an approximately spherical cell in a uniform external field. Those conditions define the geometry and field arrangement used for the prediction, while the position term captures where the cell lies relative to the field. Stating these assumptions is important when interpreting calculated voltages in biological experiments.
To apply the Schwan equation, researchers specify the external field, cell radius, membrane properties, exposure time, and cell position relative to the field. They then account for membrane charging through the time constant and estimate the resulting transmembrane voltage. Comparing that estimate with a critical level supports interpretation of the experimental response.
Electroporation, electrofusion, and electrical stimulation are three contexts in which the calculation can organize experimental interpretation. By connecting applied electrical conditions with estimated membrane voltage, the equation helps researchers examine whether an exposure reaches a critical level and relate that estimate to changes in membrane permeability or broader cellular behavior.
Within biology, the model provides a quantitative bridge between an electrical treatment and a cell-level response. Its predicted voltage can be used to interpret observations from experiments in which membrane permeability or cellular behavior changes after exposure. This makes the calculation useful for organizing electrical-stimulation studies as well as electroporation and electrofusion work.