University:
York University
Course:
SC/CHEM 2011 | Introduction to Thermodynamics
Academic year:

2022
Views:

53

Pages:

1
Author:

Niklas

Standard enthalpy of formation → (ΔHf°) for the is the enthalpy change for the formation of 1 mole of substance under standard conditions is formed from constituent elements → called a formation rxn → 1 mole of substance (standard conditions) → Standard state: state of substance under standard conditions → reference state: form of element which is most stable under standard conditions TABLE 2.2.2 REFERENCE STATES OF SELECTED ELEMENTS ELEMENT REFERENCE ELEMENT REFERENCE STATE STATE Hydrogen H2(g) Sulfur S8(s) Carbon C(graphite) Chlorine Cl2(g) Nitrogen N2(g) Phosphorus P4(s) Oxygen O2(g) Mercury Hg(l) Some chemicals exist in 2 or more forms called allotropes (ex) allotropes of carbon graphite, graphene, diamond most stable allotrope → reference state examples of formation rxns H2(g) + 1/2O2(g) → H2O(l) ΔHf° = -285.8 kJ/mol^-1 Ag(s) + 1/2Cl2(g) → AgCl(s) ΔHf° = -127.1 kJ/mol^-1 1/2N2(g) + O2(g) → NO2(g) ΔHf° = 33.2 kJ/mol^-1 (ΔHf°) standard conditions) = 0 (ΔHf°) under standard conditions is NOT 0 if not in ref state Standard enthalpies (not rel.state) determined empirically (table given)