GCSE Combined Science (AQA)

622 videos | 38 hours

Atomic structure and the periodic table A simple model of the atom, symbols, relative atomic mass, electronic charge and isotopes

Chemical Equations

4:28 Chemical Reactions and Equations
Spec 4.1.1.1 4.3.1.1
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  • In chemical reactions, substances that react together are called reactants.
  • Example: Magnesium and sulfuric acid are reactants.
  • Products are substances produced after reactants react.
  • Example: Magnesium and sulfuric acid produce magnesium sulfate and hydrogen gas.
  • Chemical reactions can be represented by word equations.
  • Example word equation: Magnesium + sulfuric acid ��� magnesium sulfate + hydrogen.
  • Reactants are on the left of the arrow, products on the right.
  • The arrow shows the direction of the reaction.
  • Plus signs indicate reactants reacting together or multiple products.
  • Understanding word equations is important for exams.
  • Chemical reactions can also be written as symbol equations.
  • Symbol equations use chemical formulas for reactants and products.
  • Example: Magnesium (Mg) and sulfur (S) react to form magnesium sulfide (MgS).
  • Numbers in symbol equations multiply the atoms or molecules that follow.
  • Example: 2 H��� + O��� ��� 2 H���O indicates two hydrogen molecules and two water molecules.
  • Subscripts indicate the number of atoms in a molecule.
  • Multipliers apply to the entire molecule; subscripts apply to the symbol they follow.
  • Numbers in symbol equations are read with the formula, e.g., "two H��� reacts with O��� to form two H���O."

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