Stoichiometry and Chemical Quantities

Manual: General · Subject: Chemistry

Master mole calculations, limiting reagents, percent yield, and solution concentrations.

The mole as a counting unit

Moles and mass

The mole links microscopic particles to measurable quantities. One mole contains $6.022\times10^{23}$ entities, and molar mass in $\mathrm{g\,mol^{-1}}$ converts between mass and amount of substance.

Stoichiometry workflow

1

Step 1: Balance the equation.
2

Step 2: Convert known quantities to moles.
3

Step 3: Use mole ratios from the balanced equation.
4

Step 4: Convert moles to the desired unit.

Yield and excess reactants

The limiting reagent is the reactant that runs out first and sets the maximum theoretical yield. Percent yield is $\%\text{yield} = \frac{\text{actual yield}}{\text{theoretical yield}}\times 100\%.$

Common concentration units

Unit	Meaning	Typical use
Molarity, $M$	Moles solute per liter solution	Reaction calculations
Molality, $m$	Moles solute per kilogram solvent	Colligative properties
Mass percent	Mass of solute divided by total mass	Composition by mass

How many moles are in $18.0\,\mathrm{g}$ of water, $H_2O$ ?

0.50

mol

1.00

mol

18.0

mol

2.00

mol

What is the limiting reagent?

💡

Dimensional analysis

Write units at every step. If the units cancel correctly, your setup is usually right.

If a reaction has a theoretical yield of $25.0\,\mathrm{g}$ and an actual yield of $20.0\,\mathrm{g}$ , what is the percent yield?

20\%

75\%

80\%

125\%

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Stoichiometry and Chemical Quantities

The mole as a counting unit

Moles and mass

Stoichiometry workflow

Yield and excess reactants