Question

Calculate the enthalpy change for the hydrolysis of 2 moles of magnesium bromide, MgBr2, in water, given that the standard enthalpy change of formation of magnesium oxide, MgO, is -601.6 kJ/mol and the standard enthalpy change of formation of hydrogen bromide, HBr, is -36.3 kJ/mol.

Answer 1

To calculate the enthalpy change for the hydrolysis of magnesium bromide, we first need to write the balanced chemical equation for the reaction:MgBr2  s  + 2H2O  l   MgO  s  + 2HBr  aq Next, we will use Hess's Law, which states that the enthalpy change of a reaction is the sum of the enthalpy changes of formation of the products minus the sum of the enthalpy changes of formation of the reactants.H reaction  =  Hf products  -  Hf reactants For this reaction, the enthalpy change of formation for MgO is given as -601.6 kJ/mol, and for HBr, it is -36.3 kJ/mol. Since there is no enthalpy change of formation for elements in their standard state  MgBr2 and H2O , we can calculate the enthalpy change for the reaction as follows:H reaction  = [1   -601.6  + 2   -36.3 ] - [0 + 0]H reaction  =  -601.6 - 72.6  kJ/molH reaction  = -674.2 kJ/molNow, we need to find the enthalpy change for 2 moles of MgBr2:H 2 moles  = 2   -674.2  kJH 2 moles  = -1348.4 kJSo, the enthalpy change for the hydrolysis of 2 moles of magnesium bromide in water is -1348.4 kJ.