Enthalpy of Reaction

Question

Using standard heats of formation, calculate the standard enthalpy change for the following reaction.

2HBr(g) + Cl₂(g)2HCl(g) + Br₂(g)

ANSWER:___ kJ

Answer 1

It will be the standard heat of formation of HCl (x2) + standard heat of formation of Br₂ minus the standard heat of formation of HBr (x2) + the standard heat of formation of Cl₂. Look up the values in a table and do the calculations. Standard heats of formation for Br₂ and Cl₂ will be zero, so you basically have

2 x H_formation HCl - 2 x H_formation HBr