View Virtual Lab 4

• Thermally activated processes (Java 1.5) [Opens in a separate window]
  
  

In order to reach the stable state, a ball must first be activated by getting sufficient energy from the bath to reach the activated (middle) platform. Once on the activated platform, some balls will fall to the right onto the stable platform. The number of balls reaching the stable platform in a given time is then proportional to the number of activated molecules, which we saw above is proportional to where E_a is the difference in energy between the activated and stable platforms. The rate of a thermally activated process is therefore proportional to .

If you watch the simulation for a while, you'll notice that every so often a ball gets a very strong kick from the platform. Although these strong kicks are rare, they are important since they give the system enough energy to make it to the activated state. Even small increases in temperature can substantially increase the number of times a system gets a strong enough kick to reach the activated state, represented here by the middle platform. Some thermally-activated processes take minutes or hours to occur. For instance, when you cook an egg, it takes a few minutes for the egg white to solidify and even longer for the yolk to solidify. On a molecular scale, the molecules are bouncing at about 10¹² times per second. If we were to use our simulation to model a reaction that takes one second to occur, a ball would have to bounce an average of about 10¹² times before it got a kick strong enough to knock it onto the activated platform.