Stoichiometry

Related Examples and Practice Problems

Additional Worked Out Examples/ Practice

  • Identifying classification types: Differentiation between elements, compounds or mixtures and homogeneous and heterogenous mixtures

  • Separation techniques: Selected and explaining limitation of appropriate separation

  • Relating Properties to Composition: Predicting classification based on descriptive properties

Topic Summary & Highlights
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Core Concept

Stoichiometry is the branch of chemistry that deals with the quantitative relationships between reactants and products in a chemical reaction. It allows chemists to predict how much of each substance is needed or produced in a reaction.

Practice Tips

  • Balanced Chemical Equations: Always balance the chemical equation first to ensure correct mole ratios for stoichiometric calculations.

  • Mole Ratios: Use the coefficients in the balanced equation to relate moles of one substance to another in the reaction.

  • Dimensional Analysis: Set up conversions systematically so that units cancel out, guiding you to the desired result.

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Key Concepts

Mole Ratio:

  • The coefficients in a balanced chemical equation represent the ratio of moles of each substance involved in the reaction.  

  • For example, in the reaction 2H₂ + O₂ → 2H₂O, the mole ratio is 2:1:2, meaning 2 moles of H₂ react with 1 mole of O₂ to produce 2 moles of H₂O.  

Balanced Chemical Equation:

  • A balanced equation is essential for stoichiometry calculations because it reflects the conservation of mass, with the same number of atoms of each element on both sides.  

  • Example: In 2 Al + 3 Cl₂ → 2 AlCl₃, the equation is balanced, so stoichiometry calculations can be made accurately.  

Molar Mass:

  • The molar mass (g/mol) of a substance, found on the periodic table, allows conversion between grams and moles.  

  • Example: The molar mass of H₂O is 18.02 g/mol (2 H atoms at 1.01 g/mol each + 1 O atom at 16.00 g/mol).  

Conversions in Stoichiometry:

  • Stoichiometry problems often involve converting between grams, moles, and molecules using molar mass and Avogadro's number (6.022 x 10²³ particles/mol).

Two methods to solve

  1. Dimensional Analysis

  2. BCA Table

Dimensional Analysis

  1. Write and Balance the Chemical Equation: Ensure the equation is balanced with the correct coefficients to use in mole ratios.

  2. Convert Known Quantities to Moles: If you start with grams of a substance, convert to moles using the molar mass.

  3. Use Mole Ratios to Find Unknown Quantities: Use the mole ratio from the balanced equation to relate moles of the given substance to moles of the unknown substance.

  4. Convert Moles Back to Desired Units: If needed, convert moles back to grams or other units using molar mass.

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