|MadSci Network: Chemistry|
It is probably easier to take this question the other way around. When the total amount of random kinetic energy shared by a group of molecules increases then the thing we call temperature increases because it turns out that the amount of random kinetic energy is what a thermometer measures. The molecules that make up any object are always moving about. They can rotate, vibrate, or just travel in straight lines, some books will say “translate”, until they bounce off another molecule. Any of these motions has some energy associated with it. Thus the more quickly it spins the more rotational energy it has, the greater its rate of vibration the more vibrational energy it has and the more rapidly it travels between collisions the greater its translational, or kinetic, energy. This motion is quite random so at any given time not all the molecules will have the same kinetic energy and over time any given molecule will continually gain and lose kinetic energy as it collides with its neighbors. The result is some distribution of kinetic energies among the molecules in the sense that at any instant in time there will be a few with very little, a few with a lot, and most with some amount in between. The most likely shape of this distribution of kinetic energies is called the Maxwell-Boltzmann distribution and there should be a figure in your Chemistry text showing it. It shows that the greater the total amount of random kinetic energy shared between the molecules as they collide the greater the number that will have a lot of energy. The exact shape of the curve is determined by the Temperature. When you place a thermometer in contact with a material the molecules in the material collide with the molecules of the thermometer and cause them to come to the same average random kinetic energy as the material. All of this jostling around will cause the liquid column in the thermometer to expand if the amount of jostling increases and vice versa. As far as reaction rates are concerned if the molecules move faster then they hit harder. They may also hit more often but what is usually most important is that the faster they are moving when they collide the more likely they are to have enough collision energy to make and/or break bonds to form new molecules with a different structure. Chemistry is a pretty violent process for the most part from a molecules point of view. As a chemist I find it very useful to try and imagine how the world around me would look of I were a molecule and this random shuffling about of different energies is a big part of that picture. Good luck with your chemistry and I hope you find the molecular world as fascinating as I have.
Try the links in the MadSci Library for more information on Chemistry.