Calculate the amount of heat absorbed (in kJ) when 35.15 g of CO2 reacts.

Question

2Fe₃O₄ (s) + CO₂ (g)  3Fe₂O₃ (s) + CO (g)     H = 47.2 kJ

Answer 1

2Fe₃O₄ (s) + CO₂ (g)  3Fe₂O₃ (s) + CO (g) ... balanced equation

Since the ∆H is positive 47.2 kJ for the reaction, this tells us it is endothermic and heat is absorbed.

This value of ∆H is for the reaction as written, i.e. it is heat absorbed 1 mole of CO₂ reacts. We thus need to find out how many moles of CO₂ we have in our current problem.

Moles CO₂ = 35.15 g CO2 x 1 mol CO2/44.01 g = 0.7987 moles CO₂

Now, we can convert this to kJ as follows:

0.7987 moles CO₂ x 47.2 kJ/mole = 37.70 kJ absorbed