Power Law Kinetics
Power Law Kinetics - Related Videos
10:22
Demonstration of the Power Law Model Through Extrusion
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2023
Source: Kerry M. Dooley and Michael G. Benton, Department of Chemical Engineering, Louisiana State University, Baton Rouge, LA Polymer melts are often formed into simple shapes or "extrudates", such as cylindrical pellets, flat sheets, or pipe, using an extruder.1 Polyolefins are among the most common extrudable polymers. Extrusion involves transporting and melting solid feed, which is sometimes mixed with non-polymeric materials, and the pressure build-up and transport of the melt or mixture.
02:34
Kinetic Molecular Theory and Gas Laws Explain Properties of Gas Molecules
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2020
The test of the kinetic molecular theory (KMT) and its postulates is its ability to explain and describe the behavior of a gas. The various gas laws (Boyle’s, Charles’s, Gay-Lussac’s, Avogadro’s, and Dalton’s laws) can be derived from the assumptions of the KMT, which have led chemists to believe that the assumptions of the theory accurately represent the properties of gas molecules. The Kinetic Molecular Theory Explains the Behavior of Gases Recalling that gas pressure is exerted by rapidly...
02:38
Third Law of Thermodynamics
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2020
A pure, perfectly crystalline solid possessing no kinetic energy (that is, at a temperature of absolute zero, 0 K) may be described by a single microstate, as its purity, perfect crystallinity,and complete lack of motion means there is but one possible location for each identical atom or molecule comprising the crystal (W = 1). According to the Boltzmann equation, the entropy of this system is zero. This limiting condition for a system’s entropy represents the third law of thermodynamics: the...
08:07
Enzyme Assays and Kinetics
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2023
Enzyme kinetics describes the catalytic effects of enzymes, which are biomolecules that facilitate chemical reactions necessary for living organisms. Enzymes act on molecules, referred to as substrates, to form products. Enzyme kinetic parameters are determined via assays that directly or indirectly measure changes in substrate or product concentration over time. This video will cover the basic principles of enzyme kinetics (including rate equations) and kinetic models. The concepts governing...
10:49
Determining Rate Laws and the Order of Reaction
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2023
Source: Laboratory of Dr. Neal Abrams — SUNY College of Environmental Science and Forestry All chemical reactions have a specific rate defining the progress of reactants going to products. This rate can be influenced by temperature, concentration, and the physical properties of the reactants. The rate also includes the intermediates and transition states that are formed but are neither the reactant nor the product. The rate law defines the role of each reactant in a reaction and can be used to...
FAQs
The exponents m and n determine how strongly changes in reactant concentrations influence the rate. A higher order means that a concentration change produces a larger proportional effect, while a zero-order term indicates no concentration dependence within the modeled range. Engineers use these sensitivities to identify influential reactants and estimate how operating changes may affect reactor performance.
The rate constant k captures condition-dependent behavior that is not represented by the concentration terms. Its value can change when operating conditions change, so engineers must associate it with the conditions under which the rate data were obtained. Using an appropriate k allows the model to predict rates consistently within the range for which the empirical relationship was established.
Power-law exponents summarize observed concentration effects and do not necessarily correspond to individual elementary reaction steps. This distinction matters when a complex process is represented without resolving its complete mechanism. The approach can provide a useful engineering approximation for analysis and design, but its parameters should be interpreted as model-based descriptions of measured behavior rather than definitive proof of mechanism.
Temperature and other controlling variables can alter the rate through the condition-dependent constant or through the fitted relationship itself. Consequently, a model calibrated under one set of conditions may not predict another set accurately unless those changes are represented. Engineers account for this dependence when comparing experiments, selecting operating conditions, and applying rate expressions to reactor calculations.
A typical workflow begins by measuring reaction rates while varying relevant concentrations or other controlling variables. Engineers then fit the rate expression, estimating the exponents and the condition-dependent constant from the observed relationships. The resulting model is checked against the available data before being used to calculate rates, conversion, selectivity, or residence-time requirements.
Once fitted, a rate expression supplies the kinetic term needed for reactor analysis. Engineers combine it with reactor operating information to estimate how much conversion can occur, how residence time affects performance, and what conditions may support desired selectivity. These calculations help compare designs and evaluate operating requirements without resolving every elementary reaction step.
The method is useful when a system shows measurable rate behavior but its detailed mechanism is complex, incompletely resolved, or unnecessary for the engineering objective. In catalysis, polymerization, and degradation, an empirical rate expression can organize experimental results and support prediction. Its usefulness depends on applying the fitted relationship within the conditions represented by the underlying data.
A power-law model can support predictions of reaction rate and, when incorporated into reactor analysis, conversion, selectivity, and residence-time requirements. These outcomes connect measured kinetic behavior with practical decisions about operation and design. Because the model is an approximation based on fitted relationships, engineers should interpret predictions in relation to the conditions and data used to establish it.