#5 Limiting Reactants

How many grams of water will be produced in the complete combustion of 20.0 grams of Octane, C8H18(g) and 50.0 grams Oxygen gas?

This is a limiting reagent problem just like the ones that Devron worked for you this morning.

2C8H18 + 25O2 ==> 16CO2 + 18H2O
That should get you started.
Step 1. convert grams to mols. mols = grams/molar mass

Step 2. Using the coefficients in the balanced equation, convert mols of each to mols of the H2O.

Step 3. The smaller number of mols will be the correct value to use for mols H2O produced.

Step 4. Convert to g. g = mols H2O x molar mass H2O.
Post your work if you get stuck.

To find the amount of water produced in the complete combustion of octane and oxygen, we need to determine the limiting reactant. The limiting reactant is the reactant that is completely consumed, limiting the amount of product that can be formed.

To determine the limiting reactant, we need to compare the stoichiometry of the reactants (the balanced chemical equation) with the given amounts.

First, let's write the balanced chemical equation for the combustion of octane:

C8H18 + 12.5 O2 -> 8 CO2 + 9 H2O

According to the equation, for every one mole of octane, we need 12.5 moles of oxygen gas to react completely. Now, we need to calculate the number of moles for each reactant.

Molar mass of octane (C8H18) = 114.22 g/mol
Molar mass of oxygen (O2) = 32.00 g/mol

To calculate the number of moles, we divide the given mass by the molar mass:

Moles of octane = 20.0 g / 114.22 g/mol
Moles of oxygen = 50.0 g / 32.00 g/mol

Now we have the moles of each reactant and can compare them to determine the limiting reactant. Divide the moles of each reactant by their stoichiometric coefficients (the numbers in front of the reactants in the balanced equation):

Moles of octane / 1 = moles of octane
Moles of oxygen / 12.5 = moles of oxygen

Whichever value is smaller will be the limiting reactant.

Now, multiply the moles of the limiting reactant by the corresponding stoichiometry from the balanced equation to find the number of moles of water formed. Finally, multiply the moles of water by the molar mass of water (18.015 g/mol) to find the mass of water formed.

I'll leave the calculations up to you, but feel free to ask if you have any questions along the way!