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.
A silvery, metallic substance like so many of its neighbours, its most stable form is the isotope neptunium 237 with a half life - the time it takes for half of the original amount to decay - of over 2 million years, and this is the type of neptunium most likely now to be produced as a by product from nuclear reactors.