Question

A chemistry student wants to calculate the enthalpy change (∆H) upon hydrolysis of magnesium chloride (MgCl2). The student knows that the enthalpy of formation (∆Hf) of MgCl2 is -641 kJ/mol and the enthalpy of formation of water (∆Hf) is -286 kJ/mol. The balanced chemical equation for the hydrolysis of magnesium chloride is MgCl2 + 2H2O → Mg(OH)2 + 2HCl. Calculate the enthalpy change (∆H) of this reaction.

Answer 1

To calculate the enthalpy change  H  of the reaction, we can use the following formula:H =  Hf products  -  Hf reactants First, we need to find the enthalpy of formation for the products, magnesium hydroxide  Mg OH 2  and hydrochloric acid  HCl . The enthalpy of formation of Mg OH 2 is -924 kJ/mol, and the enthalpy of formation of HCl is -92.3 kJ/mol.Now, we can plug these values into the formula:H = [1   -924 kJ/mol  + 2   -92.3 kJ/mol ] - [1   -641 kJ/mol  + 2   -286 kJ/mol ]H =  -924 - 2  92.3  -  -641 - 2  286 H =  -924 - 184.6  -  -641 - 572 H =  -1108.6  -  -1213 H = 104.4 kJ/molThe enthalpy change  H  for the hydrolysis of magnesium chloride  MgCl2  is 104.4 kJ/mol.