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StoichiometryChemistryHigh schoolabout 1:27

Grams of NH3 from 28 g of N2: animated lesson

A narrated, step-by-step stoichiometry video lesson with captions. Final answer: N2 + 3H2 → 2NH3; 28 g N2 → NH3: 34.045 g (1.999 mol).

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Video with a synthetic English voice and captions. Pick another language for subtitles in that language, or open the interactive version.

Video narrated by a synthetic voice (Piper TTS, en_US-ljspeech-high voice (LJ Speech dataset, public domain)); the steps come from our maths engine and the answer was checked independently. Download MP4 (0.5 MB) · Captions (WebVTT)

Steps on screen

1. The problem
Worked example
In the reaction N2 + H2 → NH3, how many grams of NH3 form from 28 g of N2?
2. Steps, part 1
1. $\text{N}: 2c_{1} = 1c_{3} \\ \text{H}: 2c_{2} = 3c_{3}$
  Write an atom balance for each element
2. $c_{1} = 1,\ c_{2} = 3,\ c_{3} = 2$
  Solve the linear system with the smallest whole numbers
3. $\mathrm{N_{2}} + 3\mathrm{H_{2}} \rightarrow 2\mathrm{NH_{3}}$
  Balanced equation
4. $n = \frac{28\ \text{g}}{28.014\ \text{g/mol}} = 0.9995\ \text{mol}$
  Moles of N2
3. Steps, part 2
1. $n = 0.9995 \times \frac{2}{1} = 1.999\ \text{mol},\quad m = 1.999 \times 17.031 = 34.045\ \text{g}$
  NH3 via the mole ratio 2 : 1
4. The answer
$\mathrm{N_{2}} + 3\mathrm{H_{2}} \rightarrow 2\mathrm{NH_{3}}$
N2 + 3H2 → 2NH3
5. Check
- N: 2 = 2, H: 6 = 6 ✓
- NH3 is produced in a 2 : 1 mole ratio to N2.

Transcript

The problem. Here is the problem: In the reaction N2 plus H2 → NH3, how many grams of NH3 form from 28 g of N2? Balance atoms of every element, then use the coefficients as mole ratios.

Steps, part 1. Write an atom balance for each element. Give each species an unknown coefficient; atoms of every element must be equal on both sides. Solve the linear system with the smallest whole numbers. Exact elimination leaves one free coefficient; scaling by the least common denominator gives integers. Balanced equation. Moles of N2.

Steps, part 2. NH3 via the mole ratio 2: 1.

The answer. So the answer is N2 plus 3H2 → 2NH3; 28 g N2 → NH3: 34.045 g (1.999 mol). Coefficients in a balanced equation count particles (moles), not grams. Convert grams to moles, apply the mole ratio, then convert back to grams with the other species prime molar mass. Assumes the reaction goes to completion with the known species fully consumed (or formed).

Check. N: 2 equals 2, H: 6 equals 6, which checks out. NH3 is produced in a 2: 1 mole ratio to N2.

About stoichiometry

Use a balanced equation to find how many grams of product form from a given mass of reactant.

Grams of NH3 from 28 g of N2: Animated Step-by-Step Lesson