Reacting masses and volumes

Reacting Masses and Volumes

Fundamental Concepts

  • Understand the concept of the mole as a unit of quantity in chemistry. One mole of any substance contains exactly the same number of entities, such as atoms, molecules or ions. This number is known as Avogadro’s number, which is approximately 6.02 x 10^23 entities per mole.
  • Familiarize yourself with the concept of molar mass. It’s the mass of one mole of a substance and is typically expressed in grams per mole (g/mol). It equals the sum of the relative atomic masses of all the atoms in the substance’s formula.

Balanced Chemical Equations

  • Understand that a balanced chemical equation illustrates the concept of law of conservation of mass. It signifies that the amount of mass in the reactants equals the mass in the products.
  • Learn to balance chemical formulas by ensuring the numbers of each type of atom on the left-hand side of the formula (reactants) matches with the right (products).

Reacting Masses

  • Understand that the mass of a substance involved in a chemical reaction can be calculated using the equation: mass = moles x molar mass.
  • Be able to apply this equation in problems involving reacting masses, balancing the equation to first establish the mole ratio of the reactants and products.
  • Understand that the stoichiometric coefficients (numbers in front of atoms or molecules in a chemical equation) represent the ratios of moles involved in a reaction.

Reacting Volumes

  • Recognise that Avogadro’s law states that one mole of any gas occupies the same volume at the same temperature and pressure.
  • Recognise that this molar volume is 24.0 dm^3 at room temperature and pressure (20°C and 1 atmosphere). However, the IB usually uses the value 22.4 dm^3 at STP (0°C and 1 atmosphere).
  • Be able to apply this concept to calculate volumes of gases in stoichiometric problems.

Practical Tips

  • Practice as many problems as possible involving reacting masses and volumes to get comfortable with mole conversions, balancing equations and stoichiometric calculations.
  • Always begin by writing down the balanced chemical equation and evaluating what is known and what is asked.
  • Keep the units consistent to avoid any mistakes in the calculation.