Question

Thermochemistry:

1. Calculate the amount of heat required to decompose 3.5 moles of sodium bicarbonate.

2NaHCO3 + 129 kJ  Na2CO3 + H2O + CO2

In this question, the heat of the reaction is part of the question instead of being written beside it- (What's the difference in solving between these two types of equations?) And also, do I use the heat of formation to solve this problem or what? I'm confused on where I start I think. Do I use dimensional analysis to convert to moles first?

Answer 1

I think the easy way to do this is as follows:

It reuires 129 kJ to decompose 2 mol NaHCO3 so it should require
129 x 3/2 to decompose 3.5 mols.

The difference in where the dH is written is the sign.
If you write it as you have above, it means the rxn is endothermic and you would write it this way for the other method.
2NaHCO3 ==> Na2CO3 + H2O + CO2 dH = +129 kJ but it could be written also as
+64.5 kJ/mol