SPECIFIC HEAT AND DISSOCIATION OF SIMPLE HYDROCARBONS

The specific heat at constant volume of methane, ethylene and acetylene has been computed from the vibrational frequencies involved in Raman effect and infra-red bands, and is found to agree with experiments of recent date. From the overtones of the infra-red methane band of 3022 cm−1 a heat of dissociation into probably CH3 and H of 101 cal. per mole may be deduced. The number of collisions in which the energy could be transferred from molecule to molecule is too small, however, even at 1,000 °C., to account for the splitting up of methane into CH3 and H in quartz tubes where in the initial stage catalytic effects are small. It is likely that the slower and the symmetrical vibrations lead to a lower level of dissociation into CH2 and H2, and that the finite time during which the molecule remains in these vibrational states influences the results. The need for studying the velocity of ultrasound in gases in order to gain a better knowledge of thermal decomposition processes is pointed out.