Question

The value of delta H for the reaction below is -1107kj.

2Ba (s) + O2 (g) -> 2BaO (s)

How many kJ of heat are released when 5.75 g of BaO (s) is produced?

Here is how I approached this problem:
1. Converted 5.75 g of BaO to mol:
5.75g x (1mol BaO/153.3g BaO) = 0.0375 mol BaO

2. Heat released is:
0.0375 mol BaO x (-1107 kJ / 2 mol BaO)= -20.8 kJ of heat released.

Can someone please confirm if I calculated properly. Thanks.

Answer 1

I agree with that answer.

Answer 2

There are 2 mistakes in this problem, the molar mass of Ba is 137.328 g not 153.3 g. So when you're doing your conversion, replace 153.3 with 137.3. Your answer should now be 0.0419 molBaO, not 0.0375 molBaO. On step 2, start the conversion with your new answer, 0.0419 gBaO and also make it negative (because it's releasing heat) or else you won't end with a positive answer.