How many kilojoules are absorbed when 280 g of pcl5 reacts? pcl5 (g) →pcl3 (g) + cl2 (g) δh=+67kj?

The molar mass of PCl5 is 208.24 g/mol. So calculating for the number of moles:

moles PCl5 = 280 / 208.24

moles PCl5 = 1.34 mol

From the equation, 67 kJ of heat is absorbed for every 1 mole hence:

total heat = 67 kJ / mol * 1.34 mol

total heat = 90 kJ