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 17.2 g HBr(g) reacts with sufficient Cl2(g), 8.62 kJ is evolved. Calculate the value of rH for the chemical equation given. kJ/mol

-40.5 kJ/mol

Explanation:

Step 1: Write the balanced equation

2 HBr(g) + Cl₂(g) ⇒ 2 HCl(g) + Br₂(g)

Step 2: Calculate the moles corresponding to 17.2 g of HBr

The molar mass of HBr is 80.91 g/mol.

17.2 g × 1 mol/80.91 g = 0.213 mol

Step 3: Calculate the standard enthalpy of the reaction.

By convention, when heat is evolved, ΔH° is negative. 8.62 kJ is evolved when 0.213 moles of HBr react. The standard enthalpy of the reaction is:

-8.62 kJ/0.213 mol = -40.5 kJ/mol

the volume increases