Question

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

Answer 1

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