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Related Concept Videos

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The free energy change associated with dissolving a solute in a liter of solvent is called the free energy of a solution, ΔGsolution. The overall ΔGsolution is expressed as the balance of ΔGinteraction against the always-favorable free-energy of mixing, ΔGmixing. Solution formation is favorable if  ΔGsolution is less than zero, whereas it is unfavorable if ΔGsolution is greater than zero. In short, for a solution to form and complete dissolution to take place,...
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Heat and temperature are essential concepts for everyone every day. The study of heat and temperature is part of an area of physics known as thermodynamics. It is not always easy to distinguish heat and temperature.
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Precipitation gravimetry is based on converting an analyte into a sparingly soluble precipitate, which is separated by filtration and weighed. An ideal precipitate should be pure, insoluble, of known composition, and easily filtered from the reaction mixture.
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In precipitation gravimetry, the precipitating agent should react specifically or selectively with the analyte. While a specific reagent reacts with the analyte alone, a selective reagent can react with a limited number of chemical species.
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The experimental conditions in a gravimetric analysis should be optimized to maximize the particle size and purity of the obtained precipitate. Ideally, the concentration of the precipitating reagent should be low with effective stirring to maintain low relative supersaturation for the growth of large crystals. In homogeneous precipitation, the precipitant is slowly generated by a chemical reaction in the solution to avoid local reagent excesses. For example, urea decomposes gradually to...
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Related Experiment Video

Updated: May 6, 2026

A Gusseted Thermogradient Table to Control Soil Temperatures for Evaluating Plant Growth and Monitoring Soil Processes
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An effective gravitational temperature for sedimentation.

P N Segrè1, F Liu, P Umbanhowar

  • 1Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA. Phil.Segre@msfc.nasa.gov

Nature
|February 24, 2001
PubMed
Summary

Gravitational energy fluctuations in particle suspensions act as an effective temperature, unifying low and high particle concentration behaviors. This finding clarifies complex sedimentation phenomena in fluids.

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Area of Science:

  • Fluid dynamics
  • Statistical mechanics
  • Colloidal science

Background:

  • Sedimentation of solid particles in fluids is complex and not fully understood.
  • Low particle concentrations show turbulent-like velocity correlations due to hydrodynamic interactions.
  • High particle concentrations exhibit unclear behavior due to fluid back-flow and particle interactions.

Purpose of the Study:

  • To elucidate the complex phenomena in particle sedimentation.
  • To bridge the understanding between low and high particle volume fractions (phi).
  • To identify a missing component for applying equilibrium statistical mechanics to sedimentation fluctuations.

Main Methods:

  • Investigated particle number fluctuations and their gravitational energy.
  • Applied scaling arguments to suspension viscosity and sedimentation velocity.
  • Incorporated effects of particle packing.

Main Results:

  • Gravitational energy of particle number fluctuations serves as an effective temperature.
  • High-phi sedimentation behavior is shown to be equivalent to low-phi behavior under appropriate scaling.
  • Particle packing effects are crucial for unifying sedimentation descriptions.

Conclusions:

  • An effective temperature mechanism for thermalization in sedimentation is identified.
  • A unified description of particle sedimentation across different volume fractions is achieved.
  • The study provides a new perspective on fluid-particle dynamics and statistical mechanics.