According to the following reaction, how much energy is evolved during the reaction of

According to the following reaction, how much energy is evolved during the reaction of


32.5 g B2H6 and 72.5 g Cl2? The molar mass of B2H6 is 27.67 g/mol.





B2H6(g) + 6 Cl2(g) → 2 BCl3(g) + 6 HCl(g) ΔH°rxn = -1396 kJ





A) 1640 kJ


B) 238 kJ


C) 1430 kJ


D) 3070 kJ


E) 429 kJ

Hi D again!

For this reaction, you need to convert both the given grams of B2H6 and Cl2 to moles to determine which is the limiting reactant. Once you determine the reactant that will dictate the amount of moles of product being produced, you can then solve for the amount of energy being released. So find the molar masses of B2H6 and Cl2 (27.67g and 70.9g respectively). Now convert the given masses of each compound into moles: (32,5g B2H6)(1mol/27.67g) = about 1.17 moles of B2H6, (72.5g Cl2)(1mol/70.9g) = about 1.02 moles of Cl2. Since there are less moles of Cl2 than B2H6, it is the limiting reactant and so use stoichiometry to relate the amount of Cl2 used up to the energy produced: (1.02 moles Cl2)(1396KJ/ 6 moles Cl2)=about 238 KJ. I omitted the negative sign during my calculations because the negative sign simply signifies that the energy is given off exothermically or on the product side.

Thus, the answer is B or 238 KJ produced.

I hope this helped again and feel free to ask more questions :)