Chemical Equations and Balancing

50 lessons, pages 621–670.

  1. What Is a Chemical Equation? — A shorthand record of what reacts and what forms
  2. Reactants and Products — Starting substances, new substances and which side they go on
  3. The Reaction Arrow and What It Means — Reading → as 'react to form', and why it is not an equals sign
  4. Conservation of Mass: The Core Principle — Total mass of reactants equals total mass of products
  5. Lavoisier and the Discovery of Mass Conservation — Careful weighing in sealed vessels overturns old ideas
  6. Conservation of Mass in Closed Systems — Sealed containers where nothing enters or leaves
  7. Open Systems: When Mass Seems to Change — Gases escaping or being absorbed from the air
  8. Conservation of Atoms: Why Mass Is Conserved — Atoms are rearranged, never created or destroyed
  9. Using Conservation of Mass in Calculations — Finding an unknown mass from the other masses in a reaction
  10. Word Equations: Naming Reactants and Products — Writing reactions in words with plus signs and an arrow
  11. Word Equations for Combustion — Fuels and elements burning in oxygen
  12. Word Equations for Metals and Acids — Metal + acid → salt + hydrogen
  13. Word Equations for Neutralisation — Acid + base → salt + water
  14. Word Equations for Carbonates and Acids — Acid + carbonate → salt + water + carbon dioxide
  15. Word Equations for Thermal Decomposition — One reactant breaking down on heating
  16. Word Equations for Displacement Reactions — A more reactive element taking the place of a less reactive one
  17. Naming Salts in Word Equations — How the metal and the acid decide the salt's name
  18. From Word Equations to Symbol Equations — Replacing names with correct chemical formulae
  19. Writing Correct Formulae for Reactants and Products — Using ion charges and valency to fix each formula
  20. Diatomic Elements in Equations — H₂, O₂, N₂ and the halogens as molecules
  21. Subscripts Versus Coefficients — Why formulae are fixed and only the big numbers change
  22. Counting Atoms in a Formula — Reading subscripts to tally each element
  23. Counting Atoms with Brackets and Coefficients — Multiplying through Ca(OH)₂ and 3H₂SO₄
  24. What Makes an Equation Balanced? — Equal numbers of each type of atom on both sides
  25. Balancing by Inspection: The Basic Method — Tally, adjust coefficients, re-count, repeat
  26. Balancing Simple Synthesis Reactions — Two elements combining into one compound
  27. Balancing Decomposition Reactions — One compound splitting into simpler substances
  28. Balancing Combustion of Hydrocarbons — Carbon first, hydrogen second, oxygen last
  29. Balancing Combustion of Alcohols — Accounting for oxygen already inside the fuel
  30. Balancing with Polyatomic Ions as Units — Treating sulfate, nitrate and hydroxide as single blocks
  31. Balancing Neutralisation Equations — Matching hydrogen ions with hydroxide ions
  32. Balancing Metal and Acid Reactions — Metal charge, salt formula and hydrogen gas
  33. Balancing Carbonate and Acid Reactions — Three products and how to keep track of them
  34. Balancing Displacement Reactions — Metals and halogens swapping partners
  35. Balancing Precipitation Reactions — Two soluble compounds exchanging ions
  36. Fractional Coefficients and Clearing Them — Using ½O₂ temporarily, then doubling everything
  37. The Odd–Even Strategy for Tricky Equations — Doubling an odd count to unlock a stuck balance
  38. Checking and Simplifying Coefficients — Final atom audit and the lowest whole-number ratio
  39. State Symbols in Equations — (s), (l), (g) and (aq) and what each one tells you
  40. Choosing the Correct State Symbols — Using conditions, solubility and observations
  41. Reading an Equation as Particles — Coefficients as numbers of atoms and molecules
  42. Coefficients as Reacting Ratios — How the numbers set the proportions that react
  43. Checking Mass Conservation in a Balanced Equation — Adding relative formula masses on each side
  44. Ionic Equations: An Introduction — Showing only the ions that actually change
  45. Writing Net Ionic Equations — Splitting aqueous compounds and removing spectator ions
  46. Balancing Charge as Well as Atoms — Why total charge must match on both sides
  47. Common Mistakes When Balancing Equations — Changing subscripts, lost diatomics and miscounted brackets
  48. Equations in Industry and Everyday Life — Cooking, fuels, cement and water treatment written as equations
  49. Mixed Practice: From Words to Balanced Equations — Full workflow from description to checked equation
  50. Chemical Equations and Balancing: Unit Review — Conservation of mass, word equations and balancing by inspection