Free Chemistry Dictionary

Video Example : Writing Chemical Equations

Writing Chemical Equations


  • Reactants
  • Products
  • Chemical equation
  • Notation
  • arrow
  • Atoms
  • Molecules
  • Created or destroyed
  • Principal of entropy

Definition of Writing Chemical Equations

Chemical equations describe the mixing of atoms and molecules together to achieve a reaction

More About Writing Chemical Equations

  • An arrow is used rather than an equal sign to show that the substances are being rearranged by the chemical reaction to form new substances
  • The substances being introduced to the reaction, called the reactants, must appear on the left side of the arrow, and the elements on the right of the arrow are called the products
  • Learn the atomic symbols used. Note that the symbol for an element is either a capital letter or a capital letter follower by a lower case letter. For example, C is carbon and He is helium
  • The notation for an element is a sequential listing of the atoms in the element, with each atomic symbol followed by a subscript number to indicate how many of that particular type of atom is in the element. For example, methane is made up of 1 carbon atom and 4 hydrogen atoms, and is symbolized as CH4
  • The products must be driven to react by the principal of entropy. If reactants are introduced that are capable of rearranging themselves into atoms and molecules in a lower energy state, the reaction will occur due to entropy,
  • Write the reactants on the left side of the right arrow. For example, to cause iron to rust and become ferrous oxide requires iron and oxygen, so the reactants would be Fe and O
  • Write the products on the right side of the right arrow. In the example of rusting iron, the product is ferrous oxide. The equation is thus completed as 2Fe+3/202 + nH20 → Fe2 0 3.nH20
  • Atoms cannot be created or destroyed. The atoms of each element in the inputs to the reaction must carry through to appear in the products of the reaction Thus,
  • Reactants → Products
  • Where the arrow indicates some change that occurs as a result of the process.
  • For example Aluminum (s) + Sulfuric acid (aq) →Hydrogen (g) + Aluminum sulfate (aq) Al+ H2SO4 → Al2(SO4)3 + H 2
  • The reaction must be balanced in accordance with the law of conservation of mass 2Al+ 3H2SO4 → Al2(SO4)3 + 3H 2
  • A chemical reaction equation gives the reactants and products, and a balanced chemical reaction equation shows the mole relationships of reactants and products.
  • Often, the amount of energy involved in the reaction is given. Dealing with the quantitative aspect of chemical reactions is called reaction Stoichiometry.
  • For example, when clamshells, CaCO3, are heated, a gas CO2 will be released, leaving a white powder (solid CaO) behind. This reaction is represented by the reaction as depicted in the picture, and the equation of the reaction is written as: CaCO3 →CaO + CO2