Quantitative Chemistry

• Law of Conservation of Mass


  In a chemical reaction, the total mass of the reactants equals the total mass of the products
• Matter is neither created nor destroyed during a chemical reaction
• Balanced Equation


  A chemical equation with the same number of each type of atom on both sides
• Balancing an equation


  Adjust coefficients (the numbers before molecules), not subscripts in the chemical formulas
• Relative Formula Mass (Mr)


  The sum of the relative atomic masses (Ar) of all atoms in a molecule
• Open Systems


  When reactions occur in an open system, mass can appear to change if gases enter or leave the system
• Closed Systems


  In a closed system, the mass remains constant, as no gases can escape or enter
• Accuracy


  The closeness of a measurement to the true value
• Precision


  The reproducibility of a set of measurements under unchanged conditions
• Mole


  A unit for measuring the amount of substance. One mole contains 6.022 × 10^23 particles (Avogadro's number)
• Molar Mass (M)


  The mass of one mole of a substance, equal to its relative formula mass in grams
• Use moles to quantify the amount of reactants and products
• The coefficients in a balanced chemical equation represent the ratio of moles of each substance involved
• Using Moles to Balance Equations


  1. Write the unbalanced equation

  2. Convert masses of reactants/products to moles using moles = mass/molar mass

  3. Balance the equation using these mole ratios, ensuring the number of atoms of each element is equal on both sides

  4. Adjust coefficients to obtain the simplest whole-number ratio