Rate Determining Step
Rate Determining Step - Related Videos
03:08
Rate-Determining Steps
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2020
Relating Reaction Mechanisms In a multistep reaction mechanism, one of the elementary steps progresses significantly slower than the others. This slowest step is called the rate-limiting step (or rate-determining step). A reaction cannot proceed faster than its slowest step, and hence, the rate-determining step limits the overall reaction rate. The concept of rate-determining step can be understood from the analogy of a 4-lane freeway with a short-stretch of traffic-bottleneck caused due to...
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...
01:29
Reaction Mechanisms: Rate-limiting Step Approximation
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2026
The rate-determining step, or RDS, in a chemical reaction is the slowest step that determines the overall reaction rate. It is identified by using the observed rate law and typically involves approximation methods like the RDS approximation or the steady-state approximation.In the RDS approximation, also known as the rate-limiting-step or equilibrium approximation, the reaction mechanism consists of one or more reversible reactions near equilibrium, followed by a slower RDS, and then one or...
06:47
Measurement and Analysis of Extracellular Acid Production to Determine Glycolytic Rate
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Cited by 103 •
2015
Glycolysis is a defining metabolic marker in multiple biological systems. Monitoring glycolysis by measuring the extracellular flux of H+ is common, but requires correction to be quantitative and unambiguous. Here, we demonstrate how to gather and correct extracellular flux data to distinguish between respiratory and glycolytic sources of extracellular acidification.
01:20
Determination of Michaelis Constant and Maximum Elimination Rate
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2025
The Michaelis constant (KM) and the theoretical maximum process rate (Vmax) are vital parameters in the Michaelis-Menten equation, central to many biochemical reactions. They provide essential insights into enzyme kinetics and drug metabolism. These parameters can be estimated by analyzing plasma concentration data post-drug administration. A notable example of this application is phenytoin, a drug with capacity-limited kinetics. It's recommended that phenytoin should be administered at two...
FAQs
A reaction mechanism can contain several elementary steps, but their influence on the overall rate depends on their effective activation barriers under the stated conditions. The transition state associated with the largest barrier generally exerts the strongest control over progress along the reaction coordinate. This comparison helps distinguish the controlling feature of a mechanism from a superficial count of individual steps.
The controlling step is condition-dependent rather than permanently fixed for every experiment. Changing temperature alters how readily the system crosses activation barriers, while concentration changes can shift the relative influence of steps in a multistep sequence. A catalyst changes the reaction pathway and its barriers, so another step may become rate controlling under the new conditions.
The rate-determining step provides a focal point for relating an elementary reaction sequence to the observed reaction rate. By considering which transition state most strongly limits progress, chemists can interpret how reactant concentrations influence the measured rate and assess whether a proposed mechanism is consistent with experimental behavior. This connection is especially useful when comparing competing mechanisms.
Comparing the effective barriers along competing pathways indicates which route is more readily followed under specified conditions. A pathway with a more favorable controlling transition state may proceed faster, while changes in temperature, concentration, or catalysis can alter that comparison. Consequently, the analysis helps explain why reaction conditions influence not only rate, but also product selectivity.
Chemists first examine the elementary steps in the proposed mechanism and locate their transition states on a reaction coordinate. They then compare the effective activation barriers under the conditions being studied and relate the controlling barrier to the observed rate. Finally, they consider whether changes in concentration, temperature, or catalysis would alter which step governs the reaction.
Catalysis changes the reaction pathway and can modify the activation barriers associated with its elementary steps. The originally controlling barrier may therefore become less influential, allowing another step to determine the overall rate. Examining this shift helps chemists evaluate catalyst performance and understand how catalyst design can improve reaction rates while potentially affecting the pathway and selectivity.
This analysis applies to organic, inorganic, and biochemical reactions because each may proceed through multiple elementary steps. In all three areas, identifying the controlling transition state helps connect a proposed mechanism with reaction-rate behavior. It also supports comparisons among pathways and clarifies how reaction conditions influence the progress and outcome of chemically different systems.
Knowing which step controls the rate shows where changes in reaction conditions are most likely to affect the overall process. Chemists can evaluate temperature, concentration, or catalyst changes in relation to the relevant activation barrier, then examine resulting effects on rate, yield, and selectivity. This approach links mechanistic interpretation with practical decisions about improving a reaction outcome.