Given the reaction 2NO(g) O2(g) -> 2NO2(g) DH = -113.1 kJ, how many kilojoules of energy will be released

Question

Given the reaction 2NO(g) O2(g) -> 2NO2(g) DH = -113.1 kJ, how many kilojoules of energy will be released when 50.0 g of NO(g) react with excess oxygen?

Answer 1

Using your periodic table, you can find that the molar mass of NO is 30.0 g, which you will use later in your dimensional analysis.

You first start the dimensional analysis expression with the starting value of NO and convert it to kJ:

50.0 g NO X 113.1 kJ / 60.0 g NO = 94.25 kJ released

(94.3 kJ if question is asking for correct significant figures).

The 60.0 g NO was derived from the original molar mass calculation.  The equation points out that 2 moles of NO react to form 113.1 kJ. Therefore,, it is accurate to say that 60.0 g NO (2 X NO molar mass) forms 113.1 kJ.

(94.3 kJ if question is asking for correct significant figures).