And click on the Time Machine icon. Click on âSelect Diskâ. Choose your external drive and click on âUse Backup Diskâ. Time Machine will copy everything (OS, Software, Files, and Preferences) to the external hard drive.
The standard enthalpy of formation of a pure element is in its reference form its standard enthalpy formation is zero. Carbon naturally exists as graphite and diamond. The enthalpy difference between graphite and diamond is too large for both to have a standard enthalpy of formation of zero. To determine which form is zero, the more stable form of carbon is chosen. This is also the form with the lowest enthalpy, so graphite has a standard enthalpy of formation equal to zero. Table 1 provides sample values of standard enthalpies of formation of various compounds.
Carbon-12 is by far the most abundant carbon isotope, and carbon-12 and -13 are both stable. But carbon-14 is slightly radioactive: it will spontaneously decay into nitrogen-14 by emitting an anti-neutrino and an electron, with a half-life of 5730 years.he theory behind radiocarbon dating is as follows: 1  Terrestrial carbon contains virtually no carbon-14, since any that may have been present would have long since decayed into the stable nitrogen-14. 2  Carbon dioxide in the atmosphere, however, contains a mixture of carbon-12 and carbon-14 in known proportions.