Question

Calculate the standard enthalpy change for the fusion reaction of solid sodium chloride (NaCl) at 25°C, given the following information: ΔHf°[NaCl(s)] = -411 kJ/molΔHf°[Na(s)] = 108 kJ/molΔHf°[Cl2(g)] = 0 kJ/mol The balanced chemical equation for the fusion reaction of NaCl is:NaCl(s) → Na(s) + 1/2Cl2(g)

Answer 1

To calculate the standard enthalpy change for the fusion reaction of solid sodium chloride  NaCl  at 25C, we can use Hess's Law. According to Hess's Law, the total enthalpy change for a reaction is the sum of the enthalpy changes for the individual steps in the reaction.For the given reaction:NaCl s   Na s  + 1/2Cl2 g We can use the standard enthalpies of formation  Hf  for the reactants and products to calculate the enthalpy change for the reaction:Hreaction =  Hf products  -  Hf reactants Hreaction = [ 1 mol Na  Hf[Na s ]  +  0.5 mol Cl2  Hf[Cl2 g ] ] -  1 mol NaCl  Hf[NaCl s ] Hreaction = [ 1 mol  108 kJ/mol  +  0.5 mol  0 kJ/mol ] -  1 mol  -411 kJ/mol Hreaction = [108 kJ + 0 kJ] -  -411 kJ Hreaction = 108 kJ + 411 kJHreaction = 519 kJ/molSo, the standard enthalpy change for the fusion reaction of solid sodium chloride  NaCl  at 25C is 519 kJ/mol.