Question

. Given the reaction, Fe2O3 + 3 CO arrow 2 Fe + 3 CO2, if 12.0 moles of CO2 are made, then how many moles of CO were used? (Points : 3)

12.0 moles
6.0 moles
4.0 moles
3.0 moles

Answer 1

Use the stoichiometric coefficients to find moles produced. Set up a ratio using the species of interest, like so:

e.g. for a general reaction:

\(\color{red}{a}A + \color{blue}{b}B\) \(\rightleftharpoons\) \( \color{green}{c}C\)

where upper case are the species (A,B,C), and lower case (a,b,c) are the coefficients ,

\(\dfrac{n_A}{\color{red}{a}}=\dfrac{n_B}{\color{blue}{b}}=\dfrac{n_C}{\color{green}{c}}\)

From here you can isolate what you need.
For example: if you have 2 moles of B, how many moles of C can you produce?

solve algebraically: \(\dfrac{2}{\color{blue}{b}}=\dfrac{n_C}{\color{green}{c}}\rightarrow n_C=\dfrac{2*\color{green}{c}}{\color{blue}{b}}\)

Answer 2

\[ \frac{ 2c }{ b }\]

Answer 3

I think its 4 moles

Answer 4

@aaronq

Answer 5

you would set up a ratio like this:

\(\dfrac{n_{CO_2}}{3}=\dfrac{n_{CO}}{3}\)

notice that the coefficients are the same, plug in your values

\(\dfrac{12~~moles}{3}=\dfrac{n_{CO}}{3}\)

without doing anything you can see that \(n_{CO}=12~moles\) because the coefficients are the same.