How do you figure out this question?

Question

Gaseous butane will react with gaseous oxygen to produce gaseous carbon dioxide and gaseous water . suppose 2.32 g of butane is mixed with 14. g of oxygen. calculate the minimum mass of butane that could be left over by the chemical reaction. round your answer to significant digits.

Answer 1

If butane is the limiting reactant (which it is according to the calculations), how can any of it be left over. It will run out first, and there will be 0 grams left over. If you want to know the amount of O2 left over, then here's the workings:

2C₄H₁₀ + 13 O₂ ==> 8CO₂ + 10H₂O .. balanced equation

To find limiting reactant, simply divide moles of each by the corresponding coefficient:

For C4H10: 2.32 g C4H10 x 1 mol / 58.12 g = 0.03992 mols (÷2->0.019) -->LIMITING

For O2: 14. g x 1 mol / 32 g = 0.4375 mol (÷13->0.033)

Since C4H10 is limiting, we use the moles of this to find moles of O2 used up:

0.03992 mols C4H10 x 13 mols O2 / 2 mols C4H10 = 0.259 mols O2 used up

Now find moles of O2 remaining:

0.4375 mols O2 - 0.259 mols O2 = 0.1785 mols O2 left over

Now convert to grams:

0.1785 mols O2 x 32 g / mole = 5.7 g O2 left over (2 sig. figs.)

Answer 2

Hi there,

Since this question wants you to determine how much of one of the reactants remains, you will want to apply your knowledge of limiting reagents- one reactant runs out first, restricting how much product can be made overall. Once all the limiting reagent reacts completely with the same amount of the other reactant, there is some of that other reactant left over because it is in excess.

First, you want to write your equation and make sure that it is balanced so that you can find out what your mole-to-mole ratios are (Hint: The molecular formula of butane is C4H10!) You want to balance the equation C4H10 + O2-> H2O + CO2

First, you want to determine what the limiting reagent is. Pick one of the products to determine how much of it can be made. For example, if you pick CO2 start with butane and determine how much CO2 can be made by first dividing the grams of butane you are provided with in the problem and divide by the molar mass to get to number of moles of butane that you have available to use in the reaction. Multiply by the mole-to-mole ratio of C4H10 and CO2 from the balanced reaction and that will give you the number of moles of CO2. Then, do the same thing with O2 to determine how many moles of CO2 can be made from O2. The limiting reagent will be the reactant which results in fewer moles of CO2 being made.

Now that you have determined which reactant is the limiting reagent, you can use the moles of product made and the mole-to-mole ratio of the other reactant and CO2 (the reactant that isn't the limiting reagent) to see how many moles of the other reactant are necessary to make that amount of CO2. Use molar mass of the reactant to get back to grams. Finally, you can subtract this amount from the total amount that you had to start with (given in the problem scenario) to get the amount that is left over.

Let me know if this helps and if you have any questions!