can someone please help me with this asap?

Question

N2 + 3 H2 → 2 NH3

1. Nitrogen reacts with hydrogen to form ammonia according to the balanced chemical equation above. For each of the following pairs of reactants, identify the limiting reactant and determine the theoretical yield of NH3 (in moles).

1.  2 moles N2, 7 moles H2

Answer 1

A limiting reagent is the reactant which is consumed completely. According to the reaction above, 1 mol of nitrogen reacts with 3 mol of hydrogen to form 2 mol of ammonia. The coefficients in the balanced chemical reaction tell us what our "stoichiometric ratios" are. For instance, the ratio of N2 to H2 used will always be in a 1:3 ratio.

You are starting with 2 mol of N2 and 7 mol of H2. To determine the theoretical yield, we first need to determine which reactant is limiting. To do this, let's figure out how much hydrogen we would need to consume all of the nitrogen.

We know every 1 mol of nitrogen needs 3 mol of hydrogen. Since we have 2 mol of nitrogen, it will take 6 mol of hydrogen to fully consume it (calculation below). Do we have enough hydrogen to completely use up the nitrogen? Yes, the question says we have 7 mol of hydrogen and we only need 6 mol to fully consume the nitrogen. Therefore, nitrogen is the limiting reagent. (Note: If we had less than 6 mol of hydrogen, then hydrogen would be the limiting reagent.) After using up the 6 mol of hydrogen, we'll have 1 mol of hydrogen leftover. Therefore, hydrogen is called the "excess reagent".

Calculation: 2 mol N2 (3 mol H2 / 1 mol N2) = 6 mol H2; 6 < 7; Nitrogen is limiting

Part 2 of the question asks us to calculate the theoretical yield. The theoretical yield is determined by the starting amount of our limiting reagent. Since we know nitrogen is our limiting reagent, we use stoichiometry starting with the amount of nitrogen we have (2 mol). Every 1 mol of nitrogen produces 2 mol of NH3. Thus, if we start with 2 mol of nitrogen, we should theoretically produce 4 mol of NH3. Our theoretical yield is 4 mol of NH3.

Calculation: 2 mol N2 x (2 mol NH3 / 1 mol N2) = 4 mol NH3