โ Scribed by Rogers, Donald W.
No coin nor oath required. For personal study only.
Although the chemical bond is a result of quantum mechanical interactions of electrons with nuclei and with each other, the atom itself is large enough to be treated classically. One way of understanding and predicting chemical properties is by treating the molecule as an aggregation of atoms bound by classical bonds and interacting with each other in a classical way. Such a study is called molecular mechanics, MM.
ENTHALPY: ADDITIVE METHODS
brings about a decrease in the f H 298 of about 5 kcal mol -1 = 21 kJ mol -1 (Fig. 19.1). For example, if we subtract 21 kJ mol -1 from f H 298 (ethane) = -84 kJ mol -1 , we get (correctly) f H 298 (propane) = -105 kJ mol -1 . Thus we can call -21 kJ mol -1 a CH 2 group enthalpy for the extension of ethane to propane. The group enthalpy is transferable to give the enthalpy change for extension of other alkanes to an alkane larger by one CH 2 group.
If this works for CH 2 , why not try it with other alkyl groups? The enthalpy of the CH 3 group must be one-half the enthalpy of formation of the ethane molecule CH 3 CH 3 , f H 298 (ethane) = -84 kJ mol -1 . Hence we take the CH 3 group enthalpy Concise Physical Chemistry, by Donald W. Rogers
๐ SIMILAR VOLUMES
Chemists are often depicted in the popular media as sinister fellows who pour a solution from beaker A into beaker B with catastrophic results. In fact, we are neither more nor less sinister than the next person and we take elaborate precautions to avoid catastrophies. Nevertheless, the process of a