In one example I use bond energies to calculate the energy per mole of sucrose and TNT (the explosive trinitrotoluene). Most students expect that TNT has more energy, but it turns out the two have about the same. So why is TNT an explosive (actually a conflagration)? TNT burns rapidly and involves a huge volume change. It is the rate of reaction (chemical kinetics) and the rapid volume change that causes the explosive damage. Then I can move to the thermodynamics overview.Read More
When I start into heat capacity I contrast the temperature of a substance with the feeling of hot and cold. A thermometer will tell you the temperature of a substance, but that does not tell you how much heat is present. If you touch something, you can tell if it is hotter or colder than your hand, but what about two substances at the same temperature?
Suppose outside it is -10 C (14 F) and there you find a piece of steel and a piece of Styrofoam. Which is colder? If you touch the steel it feels colder than the Styrofoam, but they are both at the same temperature. If you placed the steel on the Styrofoam, no heat will flow between them (Third Law of thermodynamics). Since your hand is much hotter than the objects, heat must flow from your hand into them.Read More
Although the obvious “pro” of recording is to give students the chance to listen numerous times; review the material; and listen to missed lectures, there is a huge “con” and that is they skip class and opt to listen to my lectures at home. Last year the attendance dropped to half because lectures are available on line, but this year the time has been shifted to 8:30 a.m. from 10:30. I am going to predict that very few will want to attend at that hour.Read More
One question I pose every year to my physical chemistry class of life science students in the first lecture is “Where is chemical energy stored?” Almost all of them say in chemical bonds. Ask how the energy is released, and they say “When bonds are broken.”