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.
The only chemical elements that form stable homonuclear diatomic molecules at standard temperature and pressure (STP) (or typical laboratory conditions of 1 bar and 25 Â°C) are the gases hydrogen (H 2), nitrogen (N 2), oxygen (O 2), fluorine (F 2), and chlorine (Cl 2).he only chemical elements that form stable homonuclear diatomic molecules at standard temperature and pressure (STP) (or typical laboratory conditions of 1 bar and 25 Â°C) are the gases hydrogen (H 2), nitrogen (N 2), oxygen (O 2), fluorine (F 2), and chlorine (Cl 2).