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Related Concept Videos

Concentration and Rate Law03:03

Concentration and Rate Law

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The rate of a reaction is affected by the concentrations of reactants. Rate laws (differential rate laws) or rate equations are mathematical expressions describing the relationship between the rate of a chemical reaction and the concentration of its reactants.
For example, in a generic reaction aA + bB ⟶ products, where a and b are stoichiometric coefficients, the rate law can be written as:
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Chemical reactions often occur in a stepwise fashion involving two or more distinct reactions taking place in a sequence. A balanced equation indicates the reacting species and the product species, but it reveals no details about how the reaction occurs at the molecular level. The reaction mechanism (or reaction path) provides details regarding the precise, step-by-step process by which a reaction occurs. Each of the steps in a reaction mechanism is called an elementary reaction. These...
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Dynamic Equilibrium02:20

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A reversible chemical reaction represents a chemical process that proceeds in both forward (left to right) and reverse (right to left) directions. When the rates of the forward and reverse reactions are equal, the concentrations of the reactant and product species remain constant over time and the system is at equilibrium. A special double arrow is used to emphasize the reversible nature of the reaction. The relative concentrations of reactants and products in equilibrium systems vary greatly;...
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Rate Law and Reaction Order02:33

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The rate of a reaction is affected by the concentrations of reactants. Rate laws (differential rate laws) or rate equations are mathematical expressions describing the relationship between the rate of a chemical reaction and the concentration of its reactants.
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The Integrated Rate Law: The Dependence of Concentration on Time02:39

The Integrated Rate Law: The Dependence of Concentration on Time

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While the differential rate law relates the rate and concentrations of reactants, a second form of rate law called the integrated rate law relates concentrations of reactants and time. Integrated rate laws can be used to determine the amount of reactant or product present after a period of time or to estimate the time required for a reaction to proceed to a certain extent. For example, an integrated rate law helps determine the length of time a radioactive material must be stored for its...
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Reaction Rate02:53

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The rate of reaction is the change in the amount of a reactant or product per unit time. Reaction rates are therefore determined by measuring the time dependence of some property that can be related to reactant or product amounts. Rates of reactions that consume or produce gaseous substances, for example, are conveniently determined by measuring changes in volume or pressure.
The mathematical representation of the change in the concentration of reactants and products, over time, is the rate...
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Updated: Apr 25, 2026

Unraveling Entropic Rate Acceleration Induced by Solvent Dynamics in Membrane Enzymes
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Inconvenient correlation - RT-BOLD relationship for homogeneous and fast reactions.

A Domagalik1, E Beldzik2, H Oginska3

  • 1Department of Cognitive Neuroscience and Neuroergonomics, Institute of Applied Psychology, Jagiellonian University, Krakow, Poland; Neurobiology Department, Malopolska Centre of Biotechnology, Jagiellonian University, Krakow, Poland.

Neuroscience
|August 28, 2014
PubMed
Summary
This summary is machine-generated.

Investigating reaction time (RT) in fMRI reveals significant brain activity correlations. Even small RT differences impact hemodynamic responses quadratically, emphasizing the need to control for RT in fMRI analyses.

Keywords:
RT–BOLD relationshipattentionfMRIreaction timesaccadestime on task

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Area of Science:

  • Cognitive Neuroscience
  • Neuroimaging

Background:

  • Reaction time (RT) is a key measure in experimental psychology.
  • RT is increasingly used in functional magnetic resonance imaging (fMRI) analysis.
  • Understanding RT-related brain activity is crucial but not fully elucidated.

Purpose of the Study:

  • To explore brain regions associated with saccadic reaction time using fMRI.
  • To investigate the relationship between RT and blood-oxygenation-level-dependent (BOLD) signals.
  • To quantify the impact of time on task on hemodynamic responses (HDRs).

Main Methods:

  • Implemented a spatial cueing paradigm with simultaneous fMRI and eye-tracking.
  • Utilized a simple saccadic task to evoke fast, homogeneous reactions.
  • Analyzed trial-by-trial correlations between BOLD signal and saccadic RT.

Main Results:

  • Identified widespread brain regions correlating with saccadic RT, including frontal lobes, intraparietal sulci, insular cortices, thalamus, and visual cortex.
  • Demonstrated that even minor RT variations significantly increase HDR in task-related areas.
  • Found a non-linear, quadratic relationship between RT differences and HDR increase.

Conclusions:

  • RT variations are linked to significant, non-linear hemodynamic responses in the brain.
  • Controlling for RT in fMRI is essential to prevent misinterpretation of results when comparing conditions with differing RTs.