AHA! Chemistry with Prof Bob
  • Home
  • Modules
    • 02 The nature of matter >
      • 0201 Atoms: Building blocks
      • 0202 Classification of matter
    • 05 Chemical reaction, chemical equations >
      • 0500 Overview, preview
      • 0501 Amount of substance, mole
      • 0502 Avogadro constant: How many?
      • 0503 Avogadro constant: Why that number?
      • 0504 Chemical formulas: What do they mean?
      • 0505 What can equations tell us?
      • 0506 Limiting reactants
    • 09 Solutions >
      • 0901 What is a solution?
      • 0902 Miscibility of liquids
      • 0903 Like dissolves like?
      • 0905 Dissolution of ionic salts in water
      • 0906 Can we predict solubilities of salts?
      • 0907 Solution concentration
      • 0908 Chemical species, speciation
      • 0909 Solutes: Electrolytes or non-electrolytes?
      • 0910 Electrolytes - strong or weak?
      • 0911 Concentrated, dilute, strong, weak
      • 0912 Species concentration vs. solution concentration
      • 0913 Weak electrolytes: Getting quantitative
    • 11 Dynamic chemical equilibrium >
      • 1100 Equilibrium: An overview
      • 1101 Visualising dynamic equilibrium
      • 1102 The jargon of equilibrium
      • 1103 Equilibrium constants
    • 22 Evidence from spectroscopy >
      • 2200 Overview, preview
      • 2201 Spectroscopy: Quantization of energies
      • 2202 Light: Wave-particle "duality"
      • 2203 UV-Visible spectroscopy
      • 2204 Beer's law
    • 27 Communicating chemistry >
      • 2700 Overview, preview
      • 2703 The jargon we use
  • TOC
  • Index
  • Teachers' area
    • T01 Communicating chemistry
    • T02 Beer's law
    • T03 Professional amnesia of the chemistry teaching professio
    • T04 Law of equilibrium
    • T05 Visusalizing dynamic chemical equilibrium
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​1100  dynamic chemical equilibrium 
overview, preview

The condition of dynamic chemical equilibrium can be achieved when a reaction is reversible: there can be reaction to form the “products” as well as reaction to form the “reactants”.

​If we refer to a generalized equation for a reversible reaction …
​

Picture

this means that reaction of substances A and B (the “reactants”) to form the substances C and D (the “products”) happens at the same time that C and D react to form A and B.

“Reversibility” is indicated by the double arrow symbol in the chemical equation.

In a reaction mixture in the condition of dynamic chemical equilibrium, the concentrations of reactants and products (and, therefore, the properties of the reaction mixture) do not change as time passes – not because the reaction has gone to completion, nor because nothing is happening, but because reaction forming the “products” is happening at exactly the same rate (in moles per second) as is reaction to form the “reactants”.
​

Opposite and simultaneous reactions can be difficult to visualise. In Module 1101: Visualising dynamic chemical equilibrium, Prof Bob presents a novel way of trying to do so by focussing not on the two reactions, but on whatever is the object of competition that is transferred between substances as the reactions occur.
​

The always-important issue of language is especially significant in this topic because of the large number of terms that are used whose meaning is open to misunderstanding – or at least, ambiguity. These include the terms reactant, product, forward reaction direction, backward reaction direction, shifts to the right, net reaction, shifts to the left, and spontaneous direction of reaction.

We cannot use language terms to communicate meaning unless all of the participants of a conversation understand the terms in the same way. This is the essence of Module 2703: The jargon we use.

In Module 1102: Some terminology, Prof Bob promotes awareness of the meaning of these terms (and discourages their use as far as possible). Not yet published.
​
Considering the concept of equilibrium quantitatively, it is rather remarkable that in all reaction mixtures (at the same temperature) in which a specified chemical reaction is at equilibrium, there is a particular mathematical expression of species concentrations that has the same numerical value – and this is not the case for any other function of their concentrations.

This paticular function of concentrations is called the reaction quotient (symbol Q). Its numerical value in reaction mixtures at equilibrium is called the equilibrium constant, K.  Prof Bob and Elena conversationally clarify this relationship in Module 1103: Equilibrium constants: What do they mean?


During reaction toward equilibrium the numerical value of Q changes, until equilibrium is achieved when the numerical value of Q is the same as the equilibrium constant appropriate for the temperature of the reaction mixture.

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  • Home
  • Modules
    • 02 The nature of matter >
      • 0201 Atoms: Building blocks
      • 0202 Classification of matter
    • 05 Chemical reaction, chemical equations >
      • 0500 Overview, preview
      • 0501 Amount of substance, mole
      • 0502 Avogadro constant: How many?
      • 0503 Avogadro constant: Why that number?
      • 0504 Chemical formulas: What do they mean?
      • 0505 What can equations tell us?
      • 0506 Limiting reactants
    • 09 Solutions >
      • 0901 What is a solution?
      • 0902 Miscibility of liquids
      • 0903 Like dissolves like?
      • 0905 Dissolution of ionic salts in water
      • 0906 Can we predict solubilities of salts?
      • 0907 Solution concentration
      • 0908 Chemical species, speciation
      • 0909 Solutes: Electrolytes or non-electrolytes?
      • 0910 Electrolytes - strong or weak?
      • 0911 Concentrated, dilute, strong, weak
      • 0912 Species concentration vs. solution concentration
      • 0913 Weak electrolytes: Getting quantitative
    • 11 Dynamic chemical equilibrium >
      • 1100 Equilibrium: An overview
      • 1101 Visualising dynamic equilibrium
      • 1102 The jargon of equilibrium
      • 1103 Equilibrium constants
    • 22 Evidence from spectroscopy >
      • 2200 Overview, preview
      • 2201 Spectroscopy: Quantization of energies
      • 2202 Light: Wave-particle "duality"
      • 2203 UV-Visible spectroscopy
      • 2204 Beer's law
    • 27 Communicating chemistry >
      • 2700 Overview, preview
      • 2703 The jargon we use
  • TOC
  • Index
  • Teachers' area
    • T01 Communicating chemistry
    • T02 Beer's law
    • T03 Professional amnesia of the chemistry teaching professio
    • T04 Law of equilibrium
    • T05 Visusalizing dynamic chemical equilibrium
  • Aha! Whatever
    • Playful dolphins
    • The University of Western Australia
    • Kings Park
  • Prof Bob?
    • Family
    • Travel
    • Perth
    • At work
  • Travelling
  • Contact
  • Blog
  • In four days for two days