Topic 1: Stoichiometric Relationships

1.1 States of Matter

The three states of matter 

Change of State

Types of Matter

Types of reactions

  • Combination or synthesis (Example)

  • Decomposition​​ (Example)

  • Simple replacement (Example)

  • Double replacement (Example)


  • Atom Economy

    • Definition: "Measure that accounts for the efficiency of chemical reactions by comparing the amount of reactants with the amount of products."

    • Formula:

  • Freeze-drying of foods:​ Low temperature and low pressure to sublime water, in order to maintain taste.

  • Refrigeration: Energy changes during the evaporation and condensation of a volatile fluid under changing pressure.

1.2 Amount of Substance

Relative atomic mass (Ar)

Definition: The weighted average of the atomic masses of its isotopes and their relative abundance, compared to 1/12th of a carbon-12 atom. Unit: 

Same concept is applied for Relative Molecular mass

Molecular formula

Definition: "The actual number of of atoms of each element in one compound." (Bylikin, 2014)

Example: Ethane:

Relative amount of substance

  • Formula:

Mole (n)

Definition: an SI unit defined as a fixed amount of substance. For instance, a dozen is 12 units of something, the same way a mole is                units of something.

Empirical formula

Definition: "the simplest whole number ratio of atoms of each element in one compound." (Bylikin, 2014)

Example: Ethane:

1.3 Stoichiometry


  • Stoichiometry: the quantitative method of examining the relative amounts of reactant and products.

  • Limiting agent: the reactant that will be completely consumed during the reaction.


  • Theoretical yield: the yield that is calculated.

  • Experimental yield: the yield that is obtained.

  • Difference between yields due to:

    • impurities

    • change in the conditions of a reaction

    • reverse reactions

    • side reactions

    • loss of product

  • Percentage yield:

Note: The concepts of yields are very important for industries. One important example is the Haber-Bosch process (production of ammonia).


STP (Standard temperature and pressure): 273 K and 100kPa

Molar volume of a gas

  • Definition: "the volume of 1 mole of a gas a constant at a given temperature and pressure." 

  • Assumptions:

    • Gases are made from small particles

    • Particles move in straight lines and in different directions

    • There is no kinetic energy loss

    • There is no force of attraction between molecules

  • Molar volume of a gas at STP​:

  • ​Gas Laws:
    • Formula​​:
  • Tip: this formula involves the change in temperature, pressure or volume.

Note: Temperature is always in K

  • Ideal Gas Equation:
    • Formula:


  • A quantitative and volumetric analysis

  • Generally uses indicators

  • Example: Acid-Base titrations or potentiometric titrations (not in the core syllabus)


Air bags: the use of gas laws to "play"the correlation between pressure, temperature and volume in order to quickly expand the total volume of the air bag in case of an accident.

​​Tip: this formula does not involve the change in temperature, pressure or volume.



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