How many grams of H2 are needed to produce 12.60 g of NH3

Answer 1

Hi Chris,

For this question, you want to find the percent mass of Hydrogen in the NH₃ compound. Here are the steps you want to follow. The answer is below the steps, but I encourage you to try this on your own:

1. Look on the periodic table to find the mass per mol of each individual element involved in the equation.
2. Use the percent mass formula to find the percent mass of Hydrogen in the compound: % Mass = Mass_H/Mass_NH3
3. Multiply the percent mass into the total mass of the compound to find the mass of H₂ required.

Note: The more proper method to do this is to write out the balanced equation: 3H₂ + N_{2 -->} 2NH₃ . However, it is not necessary in this specific case, because we know we have enough H₂. You MUST write out the balanced equation if the question mentions a surplus or deficiency in any of the elements involved.

ANSWER:

1. H: 1.0 g/mol (grams per mole), N: 14.0 g/mol
2. % Mass = Mass_H/Mass_NH3 = (3*1.0)/(14.0 + 3*1.0) = 3/17 = 0.1765 (17.65%)
3. Mass_H2 required = % Mass * Mass_Total = 0.1765 * 12.60g = 2.224g H₂

Note: Since you are given 4 significant figures, depending on the teacher or tester, you want to have that many significant figures in your final answer. Make sure to leave as many decimal places as possible in preliminary answers found in step 2 and even in step 1!