Van Deemter Equation

The Van Deemter Equation is a chromatographic model that relates analyte band broadening to mobile-phase velocity, helping researchers understand and optimize separation efficiency. It expresses height equivalent to a theoretical plate as the sum of eddy diffusion (A), longitudinal diffusion (B/u), and mass-transfer resistance (Cu), where u is the linear flow velocity; plotting plate height against velocity produces an optimum operating region. In chemistry, this relationship guides the selection of flow rates, particle sizes, column dimensions, and mobile phases for gas and liquid chromatography. Applying it can improve resolution, shorten analyses, and clarify why excessively slow or fast flow reduces performance.

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JoVE Core - Physics

Van der Waals Equation

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2025

The ideal gas law is an approximation that works well at high temperatures and low pressures. The van der Waals equation of state (named after the Dutch physicist Johannes van der Waals, 1837−1923) improves it by considering two factors. First, the attractive forces between molecules, which are stronger at higher densities and reduce the pressure, are considered by adding to the pressure a term equal to the square of the molar density multiplied by a positive coefficient a. Second, the volume...

The Van der Waals Equation

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2026

The ideal gas law is based on two simplifying assumptions: first, that there are no intermolecular attractions between gas molecules, and second, that the volume occupied by the molecules themselves is negligible compared with the volume of the container. However, these assumptions don't hold up under all conditions - specifically, at high pressures and low temperatures, as gas tends to deviate from ideal gas behavior.The van der Waals equation is an enhanced version of the ideal gas law,...

Real Gases: Effects of Intermolecular Forces and Molecular Volume Deriving Van der Waals Equation

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2020

Thus far, the ideal gas law, PV = nRT, has been applied to a variety of different types of problems, ranging from reaction stoichiometry and empirical and molecular formula problems to determining the density and molar mass of a gas. However, the behavior of a gas is often non-ideal, meaning that the observed relationships between its pressure, volume, and temperature are not accurately described by the gas laws. According to kinetic molecular theory, particles of an ideal gas do not exhibit...

Van de Graaff Generator

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2023

Van de Graaff generators (or Van de Graaffs) are devices used to demonstrate high voltage due to static electricity that can also be used for research. Robert Van de Graaff first built one in 1931 (based on original suggestions by Lord Kelvin) for use in nuclear physics research. Van de Graaff uses both smooth and pointed surfaces, conductors, and insulators to generate large static charges and, hence, large voltages. A substantial excess charge can be deposited on the sphere because it moves...

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)...

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