Chapter 7: Chemical Reactions and Quantities

Chapter 7: Chemical Reactions

Chemical Reactions Overview

  • Chemical change: transformation of substances into new forms with different properties and formulas.

  • Example: Iron (Fe) reacts with oxygen (O2) to form rust (Fe2O3).

Evidence of Chemical Change

  • Observable signs: bubbles, color change, solid formation, heat transfer.

Chemical Equations

  • Equations express reactants (left) and products (right).

  • Balanced equations have equal atom counts for reactants and products.

Balancing Chemical Equations

  1. Write correct formulas for reactants/products.

  2. Count atoms for each element.

  3. Use coefficients to balance.

  4. Verify the balanced equation.

Types of Reactions

  1. Combination: Two elements/compounds combine (e.g., 2 Na + Cl2 → 2 NaCl).

  2. Decomposition: One substance splits into simpler substances (e.g., 2 HgO → 2 Hg + O2).

  3. Single Replacement: One element replaces another in a compound (e.g., Zn + 2 HCl → ZnCl2 + H2).

  4. Double Replacement: Ions in compounds switch places (e.g., AgNO3 + NaCl → AgCl + NaNO3).

  5. Combustion: Carbon compounds burn in oxygen to produce CO2 and H2O (e.g., CH4 + 2 O2 → CO2 + 2 H2O + energy).

Oxidation and Reduction

  • Involves electron transfer: OIL RIG (Oxidation Is Loss, Reduction Is Gain).

  • Oxidation number rules establish how to identify oxidation and reduction in reactions.

The Mole

  • A mole (6.02 x 10^23 particles) is a measurement for quantity of substances.

  • Molar mass: mass of one mole of a substance in grams (e.g., molar mass of NaCl = 58.44 g/mol).

Molar Mass Calculations

  • To convert between grams and moles, use molar mass as a conversion factor.

Mass Calculations for Chemical Reactions

  • Use balanced equations to relate mass of reactants/products.

  • Steps: convert mass to moles, use mole ratios to find new moles, convert back to grams.

Percent Yield

  • Percent yield = (actual yield / theoretical yield) x 100%.

  • Theoretical yield is calculated from balanced equations, while actual yield is what is obtained during the experiment.

Energy in Chemical Reactions

  • Reactions require collisions with enough energy to break bonds (activation energy).

  • Exothermic: energy is released (ΔH < 0).

  • Endothermic: energy is absorbed (ΔH > 0).