Problem: Standard Enthalpies (or Heats) of Formation, ΔH°f , at 298 KSubstanceΔH°f (kJ/mol)Na(s)0.0Na(g)107.5Cl(g)121.3Cl2(g)0.0NaCl(s)-411.2Pb(s)0.0Pb(g)195.2Pb(NO3)2(s)-451.9N(g)472.7N2(g)0.0O(g)249.2O2(g)0.0O3(g)142.7Write equations for the formation of (a) NaCl(s) and (b)Pb(NO3)2(s) from their respective elements in their standard states. Include the value of ΔH°f for each equation.

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Standard enthalpy of formation (ΔH˚f) refers to the enthalpy change for the formation of 1 mole of a compound from its elements in their standard states.

(a) NaCl(s)

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Standard Enthalpies (or Heats) of Formation, ΔH°f , at 298 K


SubstanceΔH°f (kJ/mol)
Na(s)0.0
Na(g)107.5
Cl(g)121.3
Cl2(g)0.0
NaCl(s)-411.2
Pb(s)0.0
Pb(g)195.2
Pb(NO3)2(s)-451.9
N(g)472.7
N2(g)0.0
O(g)249.2
O2(g)0.0
O3(g)142.7


Write equations for the formation of (a) NaCl(s) and (b)Pb(NO3)2(s) from their respective elements in their standard states. Include the value of ΔH°f for each equation.

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