DYNAMIC EQUILIBRIUM IN CHEMICAL SYSTEMS
What is Dynamic Equilibrium?
Dynamic equilibrium refers to a closed system reaching a state of equilibrium where the rate of the forward reaction is equal to the rate of the reverse reaction such that the overall concentration of the reactants and products remain constant. Both the forward and reverse reactions are still occurring but AT THE SAME RATE such that the concentration remains unchanged.
Dynamic equilibrium refers to a closed system reaching a state of equilibrium where the rate of the forward reaction is equal to the rate of the reverse reaction such that the overall concentration of the reactants and products remain constant. Both the forward and reverse reactions are still occurring but AT THE SAME RATE such that the concentration remains unchanged.
LESSON OVERVIEW (SPECIFIC EXPECTATIONS: E2.1, E2.2, E3.1, E3.2 ,E3.3)
Diagnostic/Inquiry Based Activity:
For a lesson hook that introduces the concept of dynamic equilibrium and gets the students moving you can try a great activity published in CHEM13 News, April 2010 called "Really Dynamic Equilibrium". Ideally it would be as a diagnostic at the beginning of the unit. Click below to download a copy of "Really Dynamic Equilibrium". Before starting the activity a few key industrial processes that rely on the concept of equilibrium should be mentioned and ideally the definition of equilibrium should be established and kept in view (on a board etc.) such that students can refer to it when answering followup questions.
For a lesson hook that introduces the concept of dynamic equilibrium and gets the students moving you can try a great activity published in CHEM13 News, April 2010 called "Really Dynamic Equilibrium". Ideally it would be as a diagnostic at the beginning of the unit. Click below to download a copy of "Really Dynamic Equilibrium". Before starting the activity a few key industrial processes that rely on the concept of equilibrium should be mentioned and ideally the definition of equilibrium should be established and kept in view (on a board etc.) such that students can refer to it when answering followup questions.
Action:
Once this activity is completed, making plots of each "paper wad" scenario will allow the students to see the results of changing the "paper wad" variables on the resulting equilibrium. It is a good idea to have a few guiding questions prepared so that they can come up with their own conclusions about what has happened during the activity. Listed below are a few questions to get their minds thinking after the activity, ideally these questions would be answered individually to allow for assessment of student knowledge after the plots are completed:
Students may find the first run of the activity easy to follow as both the reactants side and products side end up with about equal concentrations but may find it difficult to believe any of the other runs (with unequal finishing concentrations) would reach equilibrium. The plots along with the above questions and possibly a reminder of the definition of equilibrium should help to clear up that common misconception. It would be ideal to introduce the method of I.C.E at this point as changing concentration can be referenced with changing amounts of "paper wads".
Once this activity is completed, making plots of each "paper wad" scenario will allow the students to see the results of changing the "paper wad" variables on the resulting equilibrium. It is a good idea to have a few guiding questions prepared so that they can come up with their own conclusions about what has happened during the activity. Listed below are a few questions to get their minds thinking after the activity, ideally these questions would be answered individually to allow for assessment of student knowledge after the plots are completed:
- Did the system come to equilibrium and how do you know?
- Does it matter if you start on the reactants side or product side? Explain why or why not.
- Was the "paper wad" concentration always the same on the reactant side and the product side once equilibrium was reached? If not, explain how this could still be equilibrium.
- If we are modelling equilibrium, why can we not stop the transfer or throwing of "paper wads"
Students may find the first run of the activity easy to follow as both the reactants side and products side end up with about equal concentrations but may find it difficult to believe any of the other runs (with unequal finishing concentrations) would reach equilibrium. The plots along with the above questions and possibly a reminder of the definition of equilibrium should help to clear up that common misconception. It would be ideal to introduce the method of I.C.E at this point as changing concentration can be referenced with changing amounts of "paper wads".
Debrief:
To summarize the activity and the introduction to equilibrium, first take up the questions as a class. As the questions are being discussed, refer to chemical equilibrium and reactions to make the connection between the activity and future lessons, changing the activity conditions with changing reaction conditions. Finish with an I.C.E. calculation replacing "paper wads" with molar concentrations for one of the runs and allow them to do the other two runs for homework.
Misconceptions Addressed: Students commonly believe nothing is happening at equilibrium.
FOPP: Leadership in learning communities and commitment to students and student learning
To summarize the activity and the introduction to equilibrium, first take up the questions as a class. As the questions are being discussed, refer to chemical equilibrium and reactions to make the connection between the activity and future lessons, changing the activity conditions with changing reaction conditions. Finish with an I.C.E. calculation replacing "paper wads" with molar concentrations for one of the runs and allow them to do the other two runs for homework.
Misconceptions Addressed: Students commonly believe nothing is happening at equilibrium.
FOPP: Leadership in learning communities and commitment to students and student learning
The concept of dynamic equilibrium can be reinforced in a variety of ways to appeal to all forms of multiple intellegences. Click below for a few resources that can be used in conjunction with a lesson to further demonstrate the concept of dynamic equilibrium.