Student Exploration: Equilibrium and Concentration
Vocabulary: chemical equilibrium, concentration, equilibrium, equilibrium constant,
... [Show More] reaction
quotient, reversible reaction
Prior Knowledge Questions (Do these BEFORE using the Gizmo.)
Gary has $5,000 in his bank account and earns a modest salary. Every month he pays for rent,
food, utilities, and entertainment.
A. How will Gary’s account change if he saves more than he spends? _it will increase.
B. How will Gary’s account change if he spends more than he saves? It will decrease.
C. What happens if Gary spends exactly as much as he saves? It will stay the same.
Gizmo Warm-up
If Gary spends exactly as much as he earns, his savings will
be in equilibrium. Equilibrium occurs when two opposing
processes occur at the same rate, leading to no net change.
In the Equilibrium and Concentration Gizmo™, you will
investigate how equilibrium can occur in chemical reactions.
To begin, check that Reaction 1 is selected. Set Moles NO2
to 8 and Moles N2O4 to 0.
1. Click Play ( ) and observe the colliding molecules. What do you notice?
the molecules move and collide. Occasionally there is a blue or red flash.
In the Gizmo, a blue flash appears every time two reactants combine to form a
product. A red flash appears every time a product dissociates into reactants.
2. Click Reset ( ), and set Moles NO2 to 0 and Moles N2O4 to 8. Click Play.
What do you notice now? There are more red flashes than blue.
3. When a reaction can proceed in either direction, it is a reversible reaction. Based on what
you have observed, is the synthesis of NO2 into N2O4 a reversible reaction? Explain.
I know the synthesis of NO2 into N2O4 is a reversible reaction because both the
forward reaction (blue flashes) and the reverse reaction (red flashes) are observed.
Activity A:
Reversible
reactions
Get the Gizmo ready:
Click Reset. Reaction 1 should be selected.
Set Moles NO2 to 8 and Moles N2O4 to 0.
Move the Sim. speed slider all the way to the right.
Question: What are the characteristics of reversible reactions?
1. Predict: Suppose you began with 8 moles of NO2 in the chamber. What do you think will
happen if you let the reaction go for a long time?
2. Test: Click Play. Select the BAR CHART tab and check that Moles is selected. Observe the
bar chart for about 30 seconds. As time goes by, what do you notice about the bars
representing moles NO2 and moles N2O4?
After a while, the bars do not move as much as at first.
3. Observe: Click Pause ( ). Select the GRAPH tab. Click the (–) zoom control on the
horizontal axis until you can see the whole graph. What do you notice?
At first, the amounts of NO2 and N2O4 change rapidly. After a while the amounts do
not change as much.
This situation, in which the overall amounts of reactants and products does not change
significantly over time, is called a chemical equilibrium.
4. Record: On the BAR CHART tab, turn on Show data values. How many moles of NO2 and
N2O4 are there right now? Moles NO2 ___4.0_______ Moles N2O4 ___2.0_______
5. Calculate: Suppose all the NO2 molecules were synthesized into N2O4. Given the equation
2NO2 ⇄ N2O4, how many moles of N2O4 would be produced? _4 moles of N2O4
6. Experiment: Click Reset. On the INITIAL SETTINGS tab, set Moles NO2 to 0 and Moles
N2O4 to 4. Click Play. Click Pause when the bars of the bar chart stop moving very much.
A. List the current amounts of each substance: Moles NO2 _4.0_____ Moles N2O4
__2.0____
B. How do these results compare to starting with 8 moles of NO2? _the resulting
amounts of NO2 and N2O4 in this experiment are very similar to the results
obtained when starting with 8 moles NO2 and 0 moles N2O4.____ [Show Less]