CHEM 1B Lecture 7: Lecture 7 Thermodynamics
Document Summary
Mainly interested in changes in enthalpy, not absolute values. Gases: pure gas at a pressure of 1 atm. Liquids/solids: pure substance is most stable form at pressure 1 atm. Temperature does not appear in definition of standard state: must be specified at all times but normally 298 k. Define a standard enthalpy of reaction, hr . Hr is standard enthalpy change in enthalpy for a reaction when all reactants and products are in their standard states. Define a standard enthalpy of formation, hf . Hf is equivalent to hr per mol of substance for formation from its elements in their standard states. Hf = 0 for a pure element in its standard state. Write equations for the formation a) nacl (s) and b) Pb(no3)2(s) from their respective elements in their standard states at 298 k. Na(s) + 1/2 cl2 (g) nacl (s) hf = -411 kj/mol. Pb (s) + n2 (g) + 3o2 (g) pb(no3)2 (s) hf .
