This virtual lab is similar to the previous lesson except that an additional platform has been added. The left platform represents the metastable state and the right platform represents the stable state. The center platform can be thought of as an activated state or an energy barrier between the two other states. In this lesson, all the balls start on the left (metastable) side of the reaction. Notice that each platform's height (i.e. the potential energy of that state) is displayed at the top of the simulation window.
To start the simulation, click the button labeled "Start". It will automatically run for 15 seconds and then stop. You may pause the simulation by clicking the button again (now labeled 'Stop') in order to more closely inspect the system at any time. The number of seconds that have elapsed while the simulation is running is displayed to the right of this button. Once 15 seconds has elapsed and the simulation has stopped, you must click the 'Reset initial configuration' button in order to run another simulation. Note that this puts the balls back over the left platform and resets the timer. It does not reset the platform heights if you have changed them.
In this exercise you will be asked to adjust the height of the platforms by dragging the top of the platform with your mouse. However, unlike the last lesson, you will not be asked to change the temperature, so the temperature slider has been disabled.
Below is a table that describes the configuration of four different simulations you need to perform. Each row in the table corresponds to a different simulation. Your task is to fill in all the empty cells. The first three empty cells (from left to right) in each row can be filled in by simply calculating Ea,forward, Ea,backward, and ΔE, where these quantities have the following definitions:
Ea,forward = Eactivated - Emetastable
Ea,backward = Eactivated - Estable
ΔE = Emetastable - Estable
In order to fill in the last empty cell in each row, you need to run the simulation and record a value displayed in the histogram window on the applet. The figure below highlights the location of the quantities you need to pay attention to on the applet.
Before running each simulation, you need to adjust the levels of the platforms in the simulation window so they match the values specified in the row you're working on. Once all the platforms are the right height, click on the button labeled "Start". The simuluation will then run for 15 seconds before stopping automatically. Once the simulation has stopped, write down the number of balls in the stable state, which can be read from the right-hand side of the histogram window.
While the simulation is running, you don't need to watch the clock. Rather, you should watch the balls crossing the activated state. In particular, pay attention to how many balls are crossing in each direction. You don't need to count them, but you should try to get a general sense for relative amounts.
After completing each row, click on the button labeled "Reset Initial Configuration" to put all the balls back in the metastable state and reset the clock.
| Configuration | Emetastable | Eactivated | Estable | Ea,forward | Ea,backward | ΔE | Balls in Stable State |
|---|---|---|---|---|---|---|---|
| 1 | 70 | 90 | 20 | ||||
| 2 | 70 | 80 | 20 | ||||
| 3 | 70 | 75 | 20 | ||||
| 4 | 70 | 75 | 65 | ||||
| 5 | 70 | 90 | 65 |