Overview
This lesson covers balancing chemical equations, the process of rusting, and the reactions of metals with oxygen, focusing on key terms, processes, and practical examples.
Balancing Chemical Equations
- Chemical equations show reactants on the left and products on the right, with an arrow indicating a reaction.
- Subscripts indicate the number of atoms of each element in a compound (e.g., CO₂ has 2 oxygens).
- Diatomic molecules (e.g., O₂, H₂) must be written with a subscript of 2 when alone.
- To balance equations, adjust coefficients (numbers in front) but never subscripts.
- Atoms cannot be created or destroyed in reactions; the number of each must be equal on both sides.
- Add a triangle (Δ) below the arrow to indicate heat was used in the reaction.
Examples of Balancing
- Water: H₂ + O₂ → H₂O is not balanced; correct form is 2H₂ + O₂ → 2H₂O.
- Magnesium oxide: 2Mg + O₂ → 2MgO balances magnesium and oxygen.
- Iron oxide: 4Fe + 3O₂ → 2Fe₂O₃ balances iron and oxygen using the lowest common multiple.
Reactions of Metals with Oxygen
- Combustion is burning in oxygen, releasing energy as light and heat.
- Magnesium burns in oxygen with a bright white flame, forming magnesium oxide (MgO).
- Iron reacts with oxygen to form iron oxide (Fe₂O₃), part of rust, often seen as orange-brown flakes.
Rust and Prevention
- Rust forms when iron reacts with moist air containing oxygen.
- Prevent rust by painting, applying oil/grease, galvanizing (zinc coating), or electroplating (chrome/zinc layer).
- Rust is corrosive, weakens metals, and increases maintenance costs.
Practice Examples and Review
- Subscript: the small number behind an element, shows atom count.
- Symbol for heat in reactions: a triangle (Δ) below the arrow.
- Ratio in MgO is 1:1, in ZnCl₂ is 1:2, in NaNO₃ is 1:1:3.
- Sodium and oxygen reaction: balanced equation 4Na + O₂ → 2Na₂O.
Key Terms & Definitions
- Combustion — Rapid chemical reaction with oxygen, releasing heat and light.
- Subscript — Small number in a formula showing atom count in a compound.
- Coefficient — Number in front of a compound indicating the number of molecules.
- Diatomic molecule — Molecule consisting of two atoms of the same element (e.g., O₂).
- Galvanizing — Protecting a metal by coating it with zinc.
- Electroplating — Using electricity to apply a metal layer for protection/shininess.
Action Items / Next Steps
- Review and practice balancing chemical equations.
- Answer practice questions provided in the lesson to consolidate understanding.
- Prepare for the next lesson on non-metals reacting with oxygen.