Question

The reaction of hydrogen bromide(g) with chlorine(g) to form hydrogen chloride(g) and bromine(g) proceeds as follows:
2HBr(g) + Cl2(g) -->2HCl(g) + Br2(g)
When 23.5 g HBr(g) reacts with sufficient Cl2(g), 11.8 kJ is evolved.

Calculate the value of △,H for the chemical equation given.

Answer 1

Answer:
The enthalpy of reaction per mole of HBr for this
reaction = ArH =-40.62 kJ/mole.
Explanation:
2HBr(g) + C12(g) > 2HC|(g) + Br2 (g)
When 23.9 g HBr(g) reacts with sufficient C12(g),
12.0 kJ of heat is evolved, calculate the value of
Ar for the chemical reaction.
Note that ArH is the enthalpy per mole for the
reaction.
Molar mass of HBr (g) = 80.91 g/mol.
Hence, 1 mole of HBr = 80.91 g
23.9 g of HBr led to the reaction giving off 12.0
kJ of heat
80.91 g of HBr will lead to the evolution of (80.91
× 12/23.9) = 40.62 kJ heat is given off.
Hence, 40.62 kJ of heat is given off per 80.91 g
of HBr.
This directly translates to that 40.62 kJ of heat is
given off per 1 mole of HBr
Hence, the heat given off per mole of HBr for
this reaction is 40.62 kJ/mole.
But since the reaction liberates heat, it means
the reaction is exothermic and the enthalpy
change for the reaction (AHrxn) is negative.

-40.62