Question

Help please need to know for an exam.
How do you do a stoichiometric calculation?

Answer 1

Basically, stoichiometric calculations include following steps :

\(\space \space \bullet \textbf{Balance the equation. }\\
\space\space \bullet \textbf{Conversion of units of a given entity to moles} \\
\space \space \bullet \textbf{Calculation of the moles yielded by the given reaction} \\
\space \space \bullet \textbf{Convert moles of wanted substance to desired units.
} \)

\(\qquad \quad\qquad \quad \quad \quad \large \color{blue} {\underline{\textbf{Balancing an equation}}} : \\
\space \textbf{Basic principle :The constituent parts of a chemical equation are } \\\textbf{ never destroyed or lost: the yield of a reaction must exactly correspond} \\\textbf{ to the original reagents. This fact holds not just for the type of elements} \\\textbf{ in the yield, but also the number. } \)

\(\textbf{The process is generally trial and error . } \)

\(\qquad \quad\qquad \large \color{blue} {\underline{\textbf{Conversion of units of a given entity to moles
}}} : \\

\textbf{Moles}(n) = \cfrac{\mathsf{Mass} \space \mathsf{ of} \space \mathsf{ sample} (m) } {\mathsf{Molar} \space\mathsf{ Mass}(M) }\) .

You can also use the ideal gas equation : \(PV = nRT \) .

[P = Pressure, V = Volume, n = Moles , R = Universal gas constant , T = Temperature ]

\(\qquad \large \color{blue} {\underline{\textbf{Calculation of the moles yielded by the given reaction
}}} : \\ \)

It is done by calculating mole ratio first.

Example : (of calculating mole ratio ) : \(4 Fe + 3 O_2 \rightarrow 2Fe_2 O_3 \) .

The above reaction means : 4 moles of Fe , 3 moles of \(O_2\) and 2 moles of \(Fe_2 O_3\) . So mole ratio is 4 : 3 : 2 .

By this , you can calculate the yield of the reaction in moles.

\(\textbf{ The fourth point involves the factors we used in the second point .}\)

Answer 2

I studied this topic from SparkNotes earlier. So, have taken some points from there also.

Here is the link : http://www.sparknotes.com/chemistry/stoichiometry/stoichiometriccalculations/section2.rhtml