Stoichiometry: Calculations With Chemical Formulas and Equations

Chemical Equations

Slide 1: Title Slide

• Title: Introduction to Chemical Equations

• Subtitle: Understanding Reactants, Products, and Balancing Equations

Slide 2: What is a Chemical Equation?

• Definition: A symbolic representation of a chemical reaction.

• Example: The combustion of hydrogen gas.

Slide 3: Example of a Chemical Equation

• Equation: 2 H₂ + O₂ → 2 H₂O

• Explanation:

  • Reactants: H₂ and O₂

  • Products: H₂O

  • Arrow (→): Represents "produces"

Slide 4: Components of a Chemical Equation

• Reactants: Substances before the reaction (left side).

• Products: Substances formed after the reaction (right side).

• Coefficients: Numbers indicating relative amounts of molecules.

• Subscripts: Indicate the number of atoms in a molecule.

Slide 5: Law of Conservation of Mass

• Concept: Atoms are neither created nor destroyed in a chemical reaction.

• Balanced Equation: Same number of atoms on both sides.

Slide 6: Balancing Chemical Equations

• Example Breakdown:

  • H₂ + O₂ → H₂O (Unbalanced)

  • 2 H₂ + O₂ → 2 H₂O (Balanced)

• Multiplication Rule: Coefficients × Subscripts = Total atoms.

Slide 7: Visual Representation

• Diagram of H₂ and O₂ reacting to form H₂O molecules.

Slide 8: Key Takeaways

• Chemical equations represent reactions symbolically.

• Reactants → Products.

• Must be balanced to follow the conservation of mass.

Balancing Chemical Equation

Slide 1: Title Slide

• Title: Balancing Chemical Equations

• Subtitle: Understanding Coefficients, Subscripts, and the Conservation of Mass

Slide 2: Writing an Unbalanced Equation

• Definition: A reaction equation that does not yet have equal atoms on both sides.

• Example: CH₄ + O₂ → CO₂ + H₂O (Unbalanced)

Slide 3: Steps to Balance an Equation

1. Identify reactants and products.

2. Write their chemical formulas.

3. Adjust coefficients to balance atom numbers.

4. Use smallest whole-number coefficients.

5. Never change subscripts (this alters substance identity).

Slide 4: Coefficients vs. Subscripts

• Subscripts: Define chemical identity (H₂O ≠ H₂O₂).

• Coefficients: Adjust only the number of molecules (2 H₂O = two water molecules).

• Rule: Only coefficients can be changed to balance equations!

Slide 5: Balancing CH₄ Combustion Reaction

Step 1: Write the unbalanced equation
CH₄ + O₂ → CO₂ + H₂O (Unbalanced)

Step 2: Balance Carbon (C)

• CH₄ has 1 C → CO₂ has 1 C (already balanced).

Step 3: Balance Hydrogen (H)

• CH₄ has 4 H → H₂O has 2 H.

• Place 2 in front of H₂O to make 4 H on both sides.

• CH₄ + O₂ → CO₂ + 2 H₂O (Still unbalanced).

Step 4: Balance Oxygen (O)

• Reactants: O₂ has 2 O atoms.

• Products: CO₂ has 2 O + 2 H₂O (each with 1 O) = 4 O atoms.

• Place 2 in front of O₂ to balance.

Final Balanced Equation:
CH₄ + 2 O₂ → CO₂ + 2 H₂O

Slide 6: Visual Representation

• Diagram: CH₄ + O₂ molecules rearrange into CO₂ + H₂O.

Slide 7: Key Takeaways

• Always balance equations by adjusting coefficients.

• Never change subscripts in chemical formulas.

• Start with elements appearing in the fewest compounds.

• Use smallest whole-number coefficients.