QCYL - Chemistry (OpenStax)

Question

Hydrogen gas, H₂, reacts explosively with gaseous chlorine, \({\bf{C}}{{\bf{l}}_{\bf{2}}}\), to form hydrogen chloride, HCl(g). What is the enthalpy change for the reaction of 1 mole of \({{\bf{H}}_{\bf{2}}}\)(g) with 1 mole of \({\bf{C}}{{\bf{l}}_{\bf{2}}}\)(g) if both the reactants and products are at standard state conditions? The standard enthalpy of formation of HCl(g) is −92.3 kJ/mol.

Step-by-Step Solution

Answer

 \({\rm{\Delta Hf^\circ }}\)for two moles of HCl = -184. 6 kJ/mol.                       

Step 1: Given reaction

The reaction of 1 mole of \({{\rm{H}}_{\rm{2}}}\)(g) with 1 mole of \({\rm{C}}{{\rm{l}}_{\rm{2}}}\)(g) is given by:

\({{\rm{H}}_{\rm{2}}}\left( {\rm{g}} \right){\rm{  +  C}}{{\rm{l}}_{\rm{2}}}\left( {\rm{g}} \right) \to {\rm{2 HCl}}\left( {\rm{g}} \right){\rm{\;\;\Delta Hf^\circ   =   - 92}}{\rm{.3 kJ/mol}}\)

The change of enthalpy of one mole of HCl is -92.3 kJ/ mol is used to find the heat produced when one mole of HCl is formed.  

Step 2: Enthalpy change

Enthalpy change refers to the heat released inside or outside a system in a reaction.

The enthalpy change is evaluated as:

\(\begin{array}{*{20}{l}}{{\rm{\Delta Hf^\circ  for one mole HCl       = \;\; - 92}}{\rm{.3 kJ/mol}}}\\\begin{array}{l}{\rm{\Delta Hf^\circ   for two moles of HCl\; =  2 \times 92}}{\rm{.3 }}\\{\rm{                                            =   - 184}}{\rm{.6 kJ/mol\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;}}\end{array}\end{array}\)