PHYSICAL SCIENCE (NEED HELP)

Question

20 grams of nitrogen reacted with 2.5 moles of hydrogen to form ammonia (NH3) gas. What is the number of moles of nitrogen. 



N₂+   3 H₂  -------- >   2NH₃

Answer should be rounded to 2 decimal places with the unit -MOLES.

Answer 1

This question is tricky because it seems more complicated than it actually is. What you need to focus on is just nitrogen (N₂). You know you have 20 g of nitrogen and are trying to determine the number of moles.

When converting from mass (g) to moles, you'll need to use the mass on the Periodic Table. Nitrogen is element 7 (on the right side) and has a mass of 14.007 grams per mole. Because its chemical formula is written as N₂, you'll need to multiply that mass by 2. The molar mass of N₂ is 28.014 g/mol. Let's look at the conversion:

Start by writing what you know, then, decide whether you'll need to divide or multiply by the molar mass. Because we're starting with grams, you'll want grams to cancel out. Therefore, you'll need to divide by the molar mass.

20 g N₂ ÷ 28.014 g/mol = 0.713929 moles

All that's left to do is round to 2 decimal places: 0.71 moles of nitrogen

Hope that helps!