I’m working on the question below and the answer is 50cm^3. Could someone help me figure this out? Thanks in advance!

A 30cm^3 sample of nitrogen was reacted with a 60cm^3 sample of fluorine according the equation:

1/2 N2(g) + 3/2 F2 (g) ----> NF3 (g)

What is the volume of the gas mixture after the reaction, at constant temperature and pressure?

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Hi! We can rewrite the equation as

N2 + 3 F2 → 2NF3

We can see that fluorine would be the limiting reactant and nitrogen is in excess. We can use the molar ratio 1 : 3 : 2 to say that 60 cm3 of fluorine will react with 20cm3 of nitrogen. Using the molar ratio we can determine the volume of NF3:

60/3 x 2 = 40 cm3

Now remember there is 10 cm3 left over of nitrogen that did not react since it was in excess. So the total volume of the gas mixture is 40 + 10 = 50 cm3

Hope this helps!

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Thank you for your answer! Would it be possible to solve this question if you hadn’t rewritten the equation initially because that’s where I was making mistakes. Furthermore, in question 46 of IMAT 2017 the total volume of gas was only based off of the limiting reactant (F2) and the leftover chlorine was not included in the final volume (if I’m not mistaken). Is there a reason why these two questions were solved differently?

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Actually in that question in 2017, there was 50 cm3 excess of chlorine added to the volume of the product. Divide 150/3 x 2 = 100 cm3 plus the 50 cm3 excess.

You can do it without rewriting but I rewrote it with whole numbers in front of the molecules so that it will be easier with the molar ratio because it’s a bit confusing with fractions! :))

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Thank you so much! You’re a lifesaver, that question has been confusing me for days.