Le Chatelier Test
Le Chatelier Test - Related Videos
02:27
Le Chatelier's Principle: Changing Concentration
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2020
A system at equilibrium is in a state of dynamic balance, with forward and reverse reactions taking place at equal rates. If an equilibrium system is subjected to a change in conditions that affects these reaction rates differently (a stress), then the rates are no longer equal and the system is not at equilibrium. The system will subsequently experience a net reaction in the direction of a greater rate (a shift) that will re-establish the equilibrium. This phenomenon is summarized by Le...
02:19
Le Chatelier's Principle: Changing Temperature
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2020
Consistent with the law of mass action, an equilibrium stressed by a change in concentration will shift to re-establish equilibrium without any change in the value of the equilibrium constant, K. When an equilibrium shifts in response to a temperature change, however, it is re-established with a different relative composition that exhibits a different value for the equilibrium constant. To understand this phenomenon, consider the elementary reaction: Since this is an elementary reaction, the...
02:32
Le Chatelier's Principle: Changing Volume (Pressure)
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2020
For gas-phase equilibria, changes in the concentrations of reactants and products can occur with altered volume and pressure. The partial pressure, P, of an ideal gas is proportional to its molar concentration, M. So changes in the partial pressures of any reactant or product are essentially changes in concentrations; therefore, these changes yield the same effects on equilibria. Aside from adding or removing reactants or products, the pressures (concentrations) of species in a gas-phase...
08:37
Le Châtelier's Principle
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2023
Source: Laboratory of Dr. Lynne O'Connell — Boston College When the conditions of a system at equilibrium are altered, the system responds in such a way as to maintain the equilibrium. In 1888, Henri-Lewis Le Châtelier described this phenomenon in a principle that states, "When a change in temperature, pressure, or concentration disturbs a system in chemical equilibrium, the change will be counteracted by an alteration in the equilibrium composition." This experiment demonstrates Le Châtelier's...
03:48
Esterification - Concepts
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2020
Esters The structure of an ester is a carbonyl with an alkyl or aryl group (R) on one side, and an oxygen bound to another alkyl or aryl group (R’) on the other side, represented by the general formula: RCOOR’. Esters can be commonly derived by an esterification reaction between a carboxylic acid and an alcohol. The hydroxyl group of the carboxylic acid is replaced by an alkyl or aryl group. Simple esters, which have low molecular weight and small R and R’ functional groups, have smells and...
FAQs
The principal expansion detected by the test comes from delayed hydration of free lime, while magnesia contributes to a lesser extent. Because these constituents hydrate after the paste has hardened, their volume-related effects can force the split mould’s indicator arms apart. The resulting arm separation provides a practical indication of potential cement soundness problems.
The split mould and indicator arms turn expansion into a measurable displacement. As the paste expands, the two arms are forced apart, increasing the indicator distance. That distance provides the observable test outcome used to estimate unsoundness. The arrangement connects a physical change within the cement paste to a practical quality-control measurement.
The boiling stage places the immersed specimen in the heated condition used to expose expansion associated with delayed hydration. This matters because free lime and, to a lesser extent, magnesia may hydrate after the paste has hardened. Heating therefore helps reveal the dimensional effect that the indicator arms are intended to register.
In a Le Chatelier Test, a cement paste sample is placed in a split mould fitted with indicator arms. The mould is then immersed in water and heated to boiling. After this treatment, the increase in distance between the indicator arms is measured. The sequence links specimen preparation and water heating to an estimate of expansion.
The increase in distance represents expansion generated mainly by delayed hydration of free lime and partly by magnesia. A greater separation indicates a stronger expansion tendency and greater concern about unsoundness. Because the measurement provides an estimate, it serves as an indicator of possible later cracking, distortion, or durability loss rather than a complete description of every construction outcome.
In engineering, the test supports cement quality control and materials testing before a binder is relied on in construction. Its result can help identify cement likely to produce later cracking, distortion, or reduced structural durability after setting. This makes the method relevant to construction quality, not merely to laboratory characterization of a cement sample.