Question

Calculate the standard enthalpy change for the precipitation reaction of solid silver chloride (AgCl) from the aqueous solution with the precipitation agent, hydrochloric acid (HCl). Given the molar enthalpies of formation of AgCl(s) and HCl(g) are -127.01 kJ/mol and -92.31 kJ/mol, respectively. The balanced equation for the reaction is: AgNO3(aq) + HCl(aq) → AgCl(s) + HNO3(aq)

Answer 1

To calculate the standard enthalpy change for the precipitation reaction, we need to use Hess's Law, which states that the enthalpy change for a reaction is the same whether it occurs in one step or several steps. We can use the enthalpies of formation of the reactants and products to determine the enthalpy change for the reaction.H_reaction =  H_f products  -  H_f reactants First, we need the enthalpies of formation for all the reactants and products. We are given the values for AgCl s  and HCl g , but we need the values for AgNO3 aq  and HNO3 aq . The standard enthalpies of formation for AgNO3 aq  and HNO3 aq  are -124.41 kJ/mol and -174.1 kJ/mol, respectively.Now, we can plug these values into the equation:H_reaction = [H_f AgCl  + H_f HNO3 ] - [H_f AgNO3  + H_f HCl ]H_reaction = [ -127.01 kJ/mol  +  -174.1 kJ/mol ] - [ -124.41 kJ/mol  +  -92.31 kJ/mol ]H_reaction =  -301.11 kJ/mol  -  -216.72 kJ/mol H_reaction = -84.39 kJ/molThe standard enthalpy change for the precipitation reaction of solid silver chloride  AgCl  from the aqueous solution with the precipitation agent, hydrochloric acid  HCl  is -84.39 kJ/mol.