Mole Ratios and Mass-to-Mass Stoichiometry

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What is reaction stoichiometry?

It is the quantitative relationship between reactants and products in a chemical reaction, determined by the coefficients in the balanced equation.

What does a coefficient in a balanced equation represent?

It indicates the relative number of particles, or relative amount in moles, of that substance in the reaction.

What is a stoichiometric factor?

It is a ratio of coefficients from a balanced chemical equation, written as a conversion factor to relate amounts of two substances.

How do you choose the orientation of a mole ratio?

Place the desired substance in the numerator and the given substance in the denominator so the given substance’s units cancel.

How do you convert moles of a product to molecules?

Multiply the product’s amount in moles by Avogadro’s number, $6.022 \times 10^{23}$ molecules per mole.

Quiz questions

1. What do the coefficients in a balanced chemical equation indicate?Answer: The relative amounts of reactants and products in the reaction.
2. For $2Al + 3I_2 \rightarrow 2AlI_3$, how many moles of $I_2$ react with $0.429\text{ mol }Al$?Answer: $0.644\text{ mol }I_2$
3. Which sequence is used to calculate the mass of one substance from the mass of another in a reaction?Answer: Convert the given mass to moles, apply the mole ratio, then convert to mass.
4. For $MgCl_2 + 2NaOH \rightarrow Mg(OH)_2 + 2NaCl$, what mass of $NaOH$ produces $16\text{ g }Mg(OH)_2$? Use molar masses of $58.3\text{ g/mol}$ for $Mg(OH)_2$ and $40.0\text{ g/mol}$ for $NaOH$.Answer: Approximately $22\text{ g }NaOH$
5. What do the coefficients in a balanced equation establish about the actual quantities used in a particular reaction?Answer: They establish relative amounts, while actual quantities can be scaled up or down.