Stoichiometry

Stoichiometry is the calculation of reactants and products in chemical reactions. In civil engineering, it's vital for calculating concrete mix ratios, neutralizing acid mine drainage, and understanding corrosion rates.

The Mole Concept

Avogadro's Number and Molar Mass

Mole (mol): The SI unit for amount of substance.
Avogadro's Number ( $N_A$ ): $6.022 \times 10^{23}$ particles per mole.
Molar Mass ( $M$ ): The mass of one mole of a substance (g/mol).
- Calculated by summing atomic masses from the periodic table.
- Example: $H_2O = (2 \times 1.008) + 15.999 = 18.015 \, g/mol$ .

Balancing Chemical Equations

Chemical equations represent the reactants converting to products. They must be balanced to satisfy the Law of Conservation of Mass.

$\text{Unbalanced:} \quad Fe + O_2 \rightarrow Fe_2O_3$ $\text{Balanced:} \quad 4Fe + 3O_2 \rightarrow 2Fe_2O_3$

Stoichiometric Calculations

Limiting Reactant

The reactant that is completely consumed first, limiting the amount of product formed.

To find it:
1. Convert all reactant masses to moles.
2. Divide moles by their stoichiometric coefficients.
3. The smallest value corresponds to the limiting reactant.

Percent Yield

The efficiency of a reaction. $\% \text{Yield} = \frac{\text{Actual Yield}}{\text{Theoretical Yield}} \times 100\%$

Actual Yield: Experimental amount obtained.
Theoretical Yield: Calculated maximum amount based on stoichiometry.

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