A chemicalchange produces a new substance whereas in a physicalchange 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 physicalchanges 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.
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 + sodiumchloride = sodium sulfate + water
Example 3:
NitricAcid + SodiumHydroxide = sodium nitrate + water