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  • In this lesson, you will learn about dynamic equilibrium, the conditions required for dynamic

  • equilibrium to be reached, and examples of systems at equilibrium.

  • Imagine you are digging a hole - you got it? Imagine, as you are digging that hole, your

  • friend is refilling it. If you are digging the hole faster than your

  • friend, the hole gets larger. If your friend is filling the hole faster

  • than you, the hole gets smaller. But if the two of you are working at the same

  • speed, there would be no change to the size of the hole.

  • The same concept can be applied to a reversible reaction.

  • If the rate of the forward reaction, reactants to products, is the same as the reverse reaction,

  • products to reactants, the reaction is said to be at equilibrium.

  • This is called a dynamic equilibrium because both processes are occurring simultaneously,

  • even though there is no overall observable change.

  • For a chemical system (such as a reaction, or phase change) to be at equilibrium, it

  • must meet two important criteria. It must be a reversible process. It must be taking

  • place in a closed system A closed system is one where there is no exchange

  • of matter, only exchange of energy. An example of a reaction at equilibrium is

  • the reaction of hydrogen and iodine in a closed container to produce hydrogen iodide.

  • At the start of the reaction, there is a high concentration of hydrogen and iodine, and

  • the concentrations decrease as hydrogen iodide is formed.

  • The concentration of hydrogen iodide increases as the forward reaction proceeds.

  • As hydrogen iodide is formed, the reverse reaction is then able to occur.

  • Over time, the concentrations of hydrogen, iodine, and hydrogen iodide remain constant.

  • So what is happening here? The reaction of hydrogen and iodine to produce

  • hydrogen iodide is occurring at the same rate as the decomposition of hydrogen iodide to

  • hydrogen and iodine. So there are no observable changes although

  • both the forward and reverse reactions are occurring.

  • The reaction has not 'stopped', but rather, has reached dynamic equilibrium.

  • What would happen to this reaction if the lid on top of the glass jar was opened?

  • Please pause the lesson to think about this, and resume when you are done.

  • If the lid was removed, the system is no longer at equilibrium as both the reactants and products,

  • or 'matter' would be able to escape the system.

  • Liquid bromine equilibrates to form gaseous bromine at room temperature.

  • Remember that this is not a 'reaction' but rather, a 'phase change'.

  • Phase changes can also reach equilibrium under the correct conditions.

  • As liquid bromine evaporates, gaseous bromine condenses.

  • Since these two processes are occurring simultaneously at the same rate, there is no observable macroscopic

  • change, but the system is in fact in dynamic equilibrium.

  • In summary, a chemical system is said to be at equilibrium when the rate of the forward

  • reaction is the same as the rate of the reverse reaction.

  • There are no observable changes but both directions of the reaction are occurring, so it is a

  • dynamic equilibrium.

In this lesson, you will learn about dynamic equilibrium, the conditions required for dynamic

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B2 US equilibrium reaction hydrogen iodide iodine dynamic

What is Dynamic Equilibrium? | The Chemistry Journey | The Fuse School

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    Wayne Lin posted on 2015/06/27
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