Question

Ammonia and hydrogen chloride gases react to form solid ammonium chloride. Two flasks are connected by a valve, one flask contains NH3 (g), and the other contains HCl(g). When the valve is opened, the gases react until one is completely consumed.

Write the equation.

What type of reaction is this?

Calculate enthalpy of the reaction at STP if one mole of each reactant is used. Standard enthalpies of formation: Hf [NH3(g)] = -46.2 kJ/mol; Hf [HCl(g)] = -92.3 kJ/mol; Hf [NH4Cl(s)] = -314.4 kJ/mol

Is the reaction spontaneous?

What is the enthalpy of this reaction considering phase changes. The standard enthalpy of condensation of gaseous ammonium chloride to solid state is Hc[NH4Cl] = -176.6 kJ/mol. Explain your answer by means of the Hess’s law.

Assume that 40.0 g of NH3 and 100 g of HCl is used at 80 degrees Celsuis in the flasks above.What will be the final pressure of the system after the reaction is complete?

Answer 1

Equation can be written as:

NH₃(g) + HCl(g) -----> NH₄Cl(s)

This is a type of acid base reaction and exothemic in nature.

Enthalpy of reaction = enthalpy of formation of products - enthalpy of formation of reactants

-314.4 kJ/mol x 1mol - {-92.3 kJ/mol x 1mol +( - 46.2 kJ/mol x 1mol)}

= -175.9 kJ

The reaction should be spontaneous as it is an acid base reaction , but here entropy is decreasing drastically from gaseous state to solid state product,so for accurate result we should do gibbs free energy change.