Chemical Equation

Chemical changes are shown using chemical equations

• One way to show a chemical reaction is to write a word equation.
• It’s not as quick as using chemical symbols and you can’t tell straight away what’s happened to each of the atoms, but it’s dead easy.
  • Here’s an example-you’re told that methane burns in oxygen giving carbon dioxide and water
  • Methane + Oxygen - Carbon Dioxide + Water
  • The molecules on the left-hand side of the equation are called reactants(because they react with each other)
  • The molecules on the right-hand side are called the products(because they’ve been produced from the reactants

Symbol equations show the atoms on both sides

• Chemical changes can be shown in a kind of shorthand using symbol equations.
• Symbol equations just show the symbols or formulas of the reactants and products
  • Magnesium + Oxygen - Magnesium Oxide
  • 2Mg + 02 - 2Mg0

Symbol equations need to be balanced

• There must always be the same number of atoms on both sides-they can’t just disappear
• You balance the equation by putting numbers in front of the formulas where needed.
  • Take this equation for reacting sulfuric acid with sodium hydroxide:
  • H2S04 + Na0H - Na2S04 + H20
• The formulas are all correct but the numbers of some atoms don’t match up on both sides
• You can’t change formulas like H2SO4 to H2SO5. You can only put numbers in front of them.
• The more you practise, the quicker you get, but all you do is this:
  • Find an element that doesn’t balance and pencil in a number to try and sort it out
  • See where it gets you. It may create another imbalance, but if so, pencil in another number and see where that gets you
  • Carry on chasing unbalanced elements and it’ll sort itself out pretty quickly