Question #f6afd
1 Answer
Here's what I got.
Explanation:
The idea here is that you need to use the stoichiometric coefficients that exist between the chemical species tha ttake part in the reaction to figure out how many molecules of reactants will actually take part in the reaction.
The balanced chemical equation for this reaction looks like this
color(red)(2)"C"_4"H"_text(10(g]) + 13"O"_text(2(g]) -> color(blue)(8)"CO"_text(2(g]) + color(purple)(10)"H"_2"O"_text((g])
Usually, you would look at the stoichiometric coefficients of the reactants and of the products as representing mole ratios. But since a mole is simply a very large collection of molecules, you can look at these ratios as being molecule ratios.
So, you have a
You know that you're starting with
30 color(red)(cancel(color(black)("molecules C"_4"H"_10))) * "13 molecules O"_2/(color(red)(2)color(red)(cancel(color(black)("molecules C"_4"H"_10)))) = "195 molecules of O"_2
Since you have fewer molecules of oxygen gas, this compound will act as a limiting reagent, i.e. it will determine how many molecules of butane actually react.
More specifically,
30 color(red)(cancel(color(black)("molecules O"_2))) * (color(red)(2)" molecules C"_4"H"_10)/(13color(red)(cancel(color(black)("molecules O"_2)))) = "4.615 molecules C"_4"H"_10
Now, it's important to realize that you're dealing with molecules, so you can't have decimal numbers, since that would imply fractions of a molecule.
So, you don't have enough oxygen to allow for
4 color(red)(cancel(color(black)("molecules C"_4"H"_10))) * "13 molecules O"_2/(color(red)(2)color(red)(cancel(color(black)("molecules C"_4"H"_10)))) = "26 molecules of O"_2
So,
4 color(red)(cancel(color(black)("molecules C"_4"H"_10))) * (color(blue)(8)" molecules CO"_2)/(color(red)(2)color(red)(cancel(color(black)("molecules C"_4"H"_10)))) = "16 molecules CO"_2
4 color(red)(cancel(color(black)("molecules C"_4"H"_10))) * (color(purple)(10)" molecules H"_2"O")/(color(red)(2) color(red)(cancel(color(black)("molecules C"_4"H"_10)))) = "20 molecules H"_2"O"
So, the reaction will consume
4 molecules of butane26 molecules of oxygen gas
and produce
16 molecules of carbon dioxide20 molecules of water
The molecules that have been consumed are no longer present in the container. Don't forget that we still have molecules of butane and of oxygen gas that did not take part in the reaction! More specifically, you will also have
30 -4 = 26 molecules of butane30 - 26 = 4 molecules of oxygen gas
Therefore, the total number of molecules present in the reaction vessel after the reaction is completed will be
overbrace(26 + 4)^("unreacted") + overbrace(16 + 20)^(color(brown)("produced")) = color(green)("66 molecules")