limiting reactants

• Limiting Reactants

  • It is rare to encounter a synthesis with exact stoichiometric amounts of reaction
  • Issues of availability may result in an excess of easily accessible reactant and limited amounts of hard to procure reactants
  • Limiting reactant is the reactant completely converted to products during a reaction
  • When the limiting reactant is used up, no more product can form
  • It determines the maximum possible amounts of product
  • The moles of products formed are determined by the starting number of moles of the limiting reactant
• Identifying Limiting Reactants

  1. Must be done in a chemical reaction to determine the amount of products produced when all the limiting reactant is converted

  2. Can be identified using the Mole ratio method and Mass method
• Percent Yield


  • Yield or reaction yield refers to the quantity of moles of a product formed in relation to the reactants consumed
  • It is usually expressed as a percentage
  • Shows the efficiency of a synthesis method
  • Calculated using the formula: Percent yield = (Actual yield / Theoretical yield) x 100%
• To calculate percent yield, refer to page 85-86 of your Gen Chem 1 book and answer Problem-Solving Practice 3-20 and 3-21
• Gas Pressure


  • One of the most important properties of gases is pressure
  • Pressure is the amount of force per unit area
  • SI unit for pressure is N/m2 or Pascal
  • Pressure exerted by Earth's atmosphere is measured using a barometer
  • Pressure measured using a barometer is usually reported in mm Hg or Torr
  • Other units of pressure include standard atmosphere (atm) and Bar
  • Conversion of pressure units: 1 atm = 760 mmHg = 760 torr = 101.325 kPa, 1 bar = 100000 Pa
• Kinetic-Molecular Theory of Gases

  • Explains the common behavior and properties found among gases
  • Gases can be compressed
  • Gases exert pressure on whatever surrounds them or their container
  • Gases expand into whatever volume is available
  • Gases mix completely with one another
  • Gases are des
• Kinetic-molecular theory of gases

  • Explains the common behavior and properties found among gases
  • Gases can be compressed
  • Gases exert pressure on whatever surrounds them or its container
  • Gases expand into whatever volume is available
  • Gases mix completely with one another
  • Gases are described in terms of their temperature and pressure, the volume occupied, and the amount of gas present
• Postulates of the Kinetic-Molecular Theory

  • A gas is composed of molecules whose size is much smaller than the distances between them
  • Gas molecules move randomly at various speeds and in every possible direction
  • Except when gases collide, forces of attraction and repulsion between them are negligible
  • When collisions between molecules occur, the collisions are elastic
  • The average kinetic energy of gas molecules is proportional to the absolute temperature
• Ideal Gases

  • Ideal gases behave exactly as described by equations relating pressure, volume, temperature, and amount of gas
  • Most gases behave nearly ideally at room temperature and atmospheric pressure
  • Equations that describe the relationship among the 4 variables of gases are called Gas Laws
  • Pressure-volume (Boyle’s Law)
  • Temperature-pressure (Charles’s Law)
  • Amount-volume (Avogadro’s Law)
  • Law of Combining Volumes (Gay-Lussac’s Law)
  • Boyle’s, Charles’s, and Avogadro’s Law were combined and called the Ideal Gas Law
• Ideal Gas Law

  • The ideal gas law summarizes the relationship among volume, temperature, pressure, and amount
  • PV = nRT
  • Where V = volume, T = temperature, n = amount in moles, P = pressure, R = ideal gas constant
  • The ideal gas constant is used to make the proportionality among the variables into an equation
• Gases in Chemical Reactions

  • When applying stoichiometry to gases, the law of combining volumes and the ideal gas law made it possible to use volumes as well as masses or molar amounts in calculations