8.4

Overview of Chemical Reactions

• Chemical reactions are fundamental to understanding chemistry and will be explored in depth throughout general chemistry courses.

• Students must learn to identify and draw various types of chemical reactions.

Types of Chemical Reactions

• Combustion Reactions

  • Involves the reaction of a substance with oxygen.

  • General Reaction Format:

  • Sample + O$<em>{2}$ → CO$</em>{2}$ + H$_{2}$O

  • Products:

  • Always produces carbon dioxide (CO$<em>{2}$) and water (H$</em>{2}$O) as primary products.

  • The specific products can vary; depending on the substance (sample) being combusted, other products can include nitrogen gas (N$<em>{2}$) or chlorine gas (Cl$</em>{2}$).

  • Common Examples:

  • Combustion of propane: C$<em>{3}$H$</em>{8}$ + O$<em>{2}$ → CO$</em>{2}$ + H$_{2}$O

  • Combustion of octane (component of gasoline): (C$<em>{8}$H$</em>{18}$) → CO$<em>{2}$ + H$</em>{2}$O

• Alkali Metal Reactions

  • Involves Group 1A alkali metals (e.g., Lithium, Sodium, Potassium).

  • General Reaction with Water Format:

  • 2 M + 2 H$<em>{2}$O → 2 MOH + H$</em>{2}$

  • Example:

  • Sodium (Na) + Water (H$<em>{2}$O) → Sodium hydroxide (NaOH) + Hydrogen gas (H$</em>{2}$)

  • Reactions can be violent due to the production of flammable hydrogen gas.

• Alkali Halide Reactions

  • A subset of alkali metal reactions that combine alkali metals with halogens.

  • General Reaction Format:

  • 2 M (solid) + X$_{2}$ (g) → 2 MX (ionic molecule)

  • Example:

  • Sodium (Na) + Chlorine gas (Cl$_{2}$) → Sodium chloride (NaCl) (Table salt)

• Halide Reactions

  • Involves reactions with halogens (Group 7A elements: F, Cl, Br) and various metals.

  • General Reaction Format:

  • M (metal) + X$_{2}$ → MX

  • Examples:

  • Iron (Fe) + Bromine (Br$<em>{2}$) → Ferric bromide (FeBr$</em>{3}$)

    • Requires consideration of reaction coefficients (e.g., 3/2 Br$_{2}$ for balancing).

  • Hydrogen (H) + Halogen → Hydrogen halide (e.g., HCl, HBr).

  • Chlorine reacting with Bromine (Cl$<em>{2}$ + Br$</em>{2}$).

Reactivity and Electron Transfer

• Reactions typically involve species that either lose electrons (metals) or gain electrons (nonmetals).

• Metals characterized by low ionization energy tend to lose electrons, whereas nonmetals tend to have high electron affinities.

Balancing Chemical Reactions

• Balancing equations requires ensuring that the number of atoms of each element is equal on both sides of the equation.

• Use of fractional coefficients is acceptable for diatomic molecules when balancing reactions.

  • Example of Fractional Use:

  • For the combustion of butane (C$<em>{4}$H$</em>{10}$):

    • C$<em>{4}$H$</em>{10}$ + O$<em>{2}$ → CO$</em>{2}$ + H$_{2}$O

    • Balancing gives: C$<em>{4}$H$</em>{10}$ + 6.5 O$<em>{2}$ → 4 CO$</em>{2}$ + 5 H$_{2}$O

    • This can also be expressed as: C$<em>{4}$H$</em>{10}$ + 13/2 O$<em>{2}$ → 4 CO$</em>{2}$ + 5 H$_{2}$O

Implications of Reactions

• Understanding chemical reactions aids in calculating the amounts of products that can be produced from given reactants.

• Percent yield calculations become crucial for determining the efficiency of reactions.

• Other concepts include identifying limiting reagents and excess reagents to optimize reaction conditions.