Changing Substances

    Cards (34)

    • A chemical change produces a new substance whereas in a physical change no new substance is produced.
    • A chemical change is irreversible whereas a physical change is reversible
    • Melting, evaporating, condensing, freezing and sublimation are examples of physical changes because they only change the state (solid, liquid or gas) of the substance
    • These processes only change the energy that each particle has (how much it moves) and not its arrangement or properties (e.g. its boiling or melting point)
    • A chemical change can be identified if there is a change in colour or temperature, or if the reaction produces light
    • In a chemical change, a new substance (or product) is always made.
    • A chemical change can also be called a chemical reaction.
    • The number and type of atoms do not change in a chemical change and are only rearranged.
    • The total overall mass is conserved in a chemical change (the mass of reactant is equal to the mass of the products).
    • Every reactant atom will become a product atoms
    • Extra atoms cannot be made and atoms cannot disappear.
    • Metals react with oxygen to produce metal oxides.
    • The general equation is:
      Example 1: Metal + Oxygen = Metal Oxide
      Example 2: Lithium + Oxygen = Lithium Oxide
      These reactions are oxidation reactions because the metals gain oxygen.
    • Reduction is the loss of oxygen
    • Oxidation is the gain of oxygen
    • Exothermic reactions transfer energy to the surroundings
    • Endothermic reactions take in energy from the surroundings
    • Acids react with some metals to produce salts and hydrogen.
      Metal + Acid = Salt + Hydrogen
    • Example 1: Copper + Hydrochloric acid = copper chloride + hydrogen
      Example 2: Sodium + Nitric Acid = Sodium Nitrate + hydrogen
    • Acids are neutralised by alkalis (e.g. soluble metal hydroxides) and bases (e.g. insoluble metals hydroxides and metal oxides) to produce salts and water.
    • Acid + Alkali = salt + water
      Acid + Base = salt + water
    • Acids are neutralised by metal carbonates to produce salts, water and carbon dioxide
    • Acid + metal carbonate = salt + water + carbon dioxide
    • The particular salt produced in any reaction between an acid and a base or alkali depends on the acid and metal in the base, alkali or carbonate
    • Hydrochloric acid produces chloride salts,
      nitric acid produces nitrate salts,
      and sulfuric acid produces sulfate salts
    • Example 1:
      Hydrochloric acid + sodium hydroxide = sodium chloride + water
    • Example 2:
      Sulfuric acid + sodium chloride = sodium sulfate + water
    • Example 3:
      Nitric Acid + Sodium Hydroxide = sodium nitrate + water
    • Example 4:
      Hydrochloric acid + sodium carbonate = sodium chloride + water + carbon dioxide
    • Example 5:
      Nitric acid + Sodium carbonate = sodium nitrate + water + carbon dioxide
    • Example 6:
      Sulfuric acid + sodium carbonate = sodium sulfate + water + carbon dioxide
    • The test for hydrogen uses a burning splint held at the open end of a test tube of the gas. Hydrogen burns rapidly with a squeaky pop sound.
    • The test for carbon dioxide uses a solution of calcium hydroxide (limewater).
    • When carbon dioxide is shaken with or bubbled through limewater the limewater turns milky (cloudy)
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