Math  /  Algebra

QuestionFor example, if a 2.00 g sample of ammonia is mixed with 4.00 g of oxygen in following reaction, use stoichiometry to determine the limiting reagent: 4NH3+5O24NO+6H2O4 \mathrm{NH}_{3}+5 \mathrm{O}_{2} \longrightarrow 4 \mathrm{NO}+6 \mathrm{H}_{2} \mathrm{O}

Studdy Solution

STEP 1

What is this asking? We've got a chemical reaction where ammonia and oxygen mix to make new stuff, and we need to figure out which one runs out first! Watch out! Don't forget to convert grams to moles – we're dealing with *molecules*, not just weight!

STEP 2

1. Calculate moles of reactants
2. Determine the limiting reactant

STEP 3

Alright, let's **start** by calculating the number of moles of each reactant.
Remember, moles are just a way to count *tons* of tiny molecules all at once!
We'll use the **molar mass** to convert from grams to moles.

STEP 4

For **ammonia** (NH3\mathrm{NH}_3), the molar mass is approximately 14.01+31.01=17.04g/mol14.01 + 3 \cdot 1.01 = 17.04 \, \mathrm{g/mol}.
We have 2.00g\mathrm{2.00 \, g} of ammonia, so the number of moles is: 2.00g17.04g/mol0.117mol \frac{2.00 \, \mathrm{g}}{17.04 \, \mathrm{g/mol}} \approx 0.117 \, \mathrm{mol} So we have about 0.117\mathbf{0.117} **moles** of ammonia ready to react!

STEP 5

Now, let's do the same for **oxygen** (O2\mathrm{O}_2).
Its molar mass is 216.00=32.00g/mol2 \cdot 16.00 = 32.00 \, \mathrm{g/mol}.
We have 4.00g\mathrm{4.00 \, g} of oxygen, so the number of moles is: 4.00g32.00g/mol=0.125mol \frac{4.00 \, \mathrm{g}}{32.00 \, \mathrm{g/mol}} = 0.125 \, \mathrm{mol} We've got 0.125\mathbf{0.125} **moles** of oxygen ready to go!

STEP 6

Now for the main event: finding the **limiting reactant**!
This is the reactant that gets used up *first*, stopping the reaction in its tracks.
We'll use the **mole ratio** from the balanced chemical equation to figure this out.

STEP 7

The balanced equation tells us that we need 44 moles of NH3\mathrm{NH}_3 for every 55 moles of O2\mathrm{O}_2.
Let's see how many moles of O2\mathrm{O}_2 we'd need to react with all of our NH3\mathrm{NH}_3: 0.117molNH35molO24molNH30.146molO2 0.117 \, \mathrm{mol} \, \mathrm{NH}_3 \cdot \frac{5 \, \mathrm{mol} \, \mathrm{O}_2}{4 \, \mathrm{mol} \, \mathrm{NH}_3} \approx 0.146 \, \mathrm{mol} \, \mathrm{O}_2

STEP 8

Uh oh!
We only have 0.125\mathbf{0.125} **moles** of O2\mathrm{O}_2, but we'd need 0.146\mathbf{0.146} **moles** to react with *all* the ammonia.
That means oxygen is our **limiting reactant**!
It's going to run out first, leaving some ammonia leftover.

STEP 9

The **limiting reactant** is **oxygen** (O2\mathrm{O}_2).

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