Chemical Reactions and Equations

Chemical Equations

• Basic word equation: Hydrogen + Oxygen → Water
• Chemical equation with state symbols:
  • Unbalanced: H2 + O2 → H_2O
  • Balanced: 2H2 + O2 → 2H_2O

Ionic Equations

• Focus on ionic equations, half equations, and redox reactions.

Example: Magnesium and Zinc Sulfate

• Reaction: Magnesium (solid) + Zinc Sulfate (aqueous) → Magnesium Sulfate (aqueous) + Zinc (solid)
  • Mg(s) + ZnSO4(aq) → MgSO4(aq) + Zn(s)
• This is a displacement reaction.

Displacement Reaction

• A more reactive element displaces a less reactive element.
  • Magnesium is more reactive than zinc, hence it displaces zinc from zinc sulfate.
• If the reverse occurs (Zinc + Magnesium Sulfate), no reaction happens because zinc is less reactive than magnesium.
  • Zn(s) + MgSO_4(aq) → No Reaction

State Symbols

• s = solid
• l = liquid
• g = gas
• aq = aqueous (dissolved in water)
  • Aqueous solutions contain ions.
  • Example: ZnSO4(aq) consists of Zn^{2+} and SO4^{2-} ions floating freely in water.

Ionic Equation Breakdown

• Mg(s) + ZnSO4(aq) → MgSO4(aq) + Zn(s)
• Mg(s) + Zn^{2+}(aq) + SO4^{2-}(aq) → Mg^{2+}(aq) + SO4^{2-}(aq) + Zn(s)
• Spectator ions: Ions that do not participate in the reaction (e.g., SO4^{2-}, which remains SO4^{2-}).
• Ionic Equation: Includes only the reacting species.
  • Mg(s) + Zn^{2+}(aq) → Mg^{2+}(aq) + Zn(s)

Half Equations

• Breaking down the ionic equation into oxidation and reduction half-reactions.

Magnesium Half-Equation

• Mg → Mg^{2+} + 2e^-
• Magnesium loses two electrons to become Mg^{2+}.

Zinc Half-Equation

• Zn^{2+} + 2e^- → Zn
• Zinc gains two electrons to become Zn.

Oxidation and Reduction (Redox)

• Oxidation: Loss of electrons.
  • Mg → Mg^{2+} + 2e^- (Magnesium is oxidized)
• Reduction: Gain of electrons.
  • Zn^{2+} + 2e^- → Zn (Zinc is reduced)
• Redox Reaction: A reaction where both oxidation and reduction occur simultaneously.

Chemical Formulas

Determining Chemical Formulas Using the Periodic Table

• Elements in the same group have similar ionic charges.
  • Group 1 elements form +1 ions.
  • Group 2 elements form +2 ions.
  • Group 3 elements form +3 ions.
  • Group 5 elements form -3 ions.
  • Group 6 elements form -2 ions.
  • Group 7 elements form -1 ions.

Examples of Ions

• Oxygen (Group 6): O^{2-}
• Nitrogen (Group 5): N^{3-}
• Lithium (Group 1): Li^{+1}
• Sodium (Group 1): Na^{+1}
• Magnesium (Group 2): Mg^{2+}
• Calcium (Group 2): Ca^{2+}

Swap and Drop Method

• Used to determine chemical formulas.

Procedure

1. Identify the ions and their charges.
2. Swap the magnitudes of the charges.
3. Drop the charges.

Example: Magnesium Chloride

• Magnesium: Mg^{2+}
• Chloride: Cl^{-1}
• Swap and Drop:
  • Mg1Cl2
• Chemical Formula: MgCl_2

Practice Examples

• Sodium Chloride: NaCl
• Magnesium Bromide: MgBr_2
• Calcium Fluoride: CaF_2
• Aluminum Oxide: Al2O3
• Magnesium Oxide: MgO

Transition Metals and Roman Numerals

• Transition metals can have multiple oxidation states (variable charges).
• Roman numerals indicate the charge of the transition metal ion.

Example: Iron (III) Oxide

• Iron (III): Fe^{3+}
• Oxide: O^{2-}
• Chemical Formula: Fe2O3

Example: Cobalt (II) Chloride

• Cobalt (II): Co^{2+}
• Chloride: Cl^{-1}
• Chemical Formula: CoCl_2

Common Ions

• Iron (II): Fe^{2+}
• Iron (III): Fe^{3+}
• Sulfate: SO_4^{2-}
• Sulfide: S^{2-}
• Carbonate: CO_3^{2-}
• Nitrate: NO_3^{-}
• Hydroxide: OH^{-}

Chemical Formula Examples with Polyatomic Ions

• Aluminum Hydroxide: Al(OH)_3
• Calcium Nitrate: Ca(NO3)2
• Sodium Nitrate: NaNO_3

Importance of Fundamentals

• Understanding chemical formulas and equations is crucial for success in chemistry.
• Practice with examples to build confidence.

Splitting Substances in Equations

• AgNO_3 and KCl are expected to be split into ions in aqueous solutions.

Applications

• Dentistry requires knowledge of chemical language (formulas and equations).