chemical changes
definition of chemical change → a change in which new substance is formed
definition of physical change → a change in which no new substances are fromed
chemical changes | physical changes |
|---|---|
new substances formed | no new substances formed |
energy in the form of heat and light produced (in some cases only) | no heat and/or light produced |
reactions are usually irreversibe | reactions are usually reversible (eg. can be separated using physical changes like filtration, evaporation to dryness, distillation) |
change in properties (eg. colour, magnetic property, electrical conductivity) | no changes in properties of substances |
types of chemical changes:
Mixing (when two or more reactants are mixed together)
acid reactions
acid + metal → salt + hydrogen
acid + base → salt + water
acid + carbonate → salt + carbon dioxide + water
Heating (when heat / increase in temperature is necessary)
thermal decomposition - the decomposition of substances
calcium carbonate → calcium oxide + water (when heated)
combustion - combination of substance with oxygen in the presence of heat
petrol + oxygen → carbon dioxide + water (when heated)
exposure to light (occur only when light is present)
photosynthesis (process whereby organisms with chlorophyll presence produce glucose and oxygen)
carbon dioxide + water → glucose + oxygen (in the presence of light)
interaction with oxygen / oxidation (any reactions involving oxygen
rusting (only for iron, other metals corrode)
iron + water + oxygen → hydrated iron (III) oxide
for rusting to occur, moisture and oxygen must be present
respiration
glucose + oxygen → carbon dioxide + water
using electric current (when a current is passed through)
electroplating (coating an object with a metal by passing an electric current through a solution)
used to coat items like trophies / coins with a thin layer of metal
used in many field (such as aesthetics, medical, manufacturing)
used to prevent corrosion on metal applainces that corrode easily