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Key C20 Notes : Physical vs Chemical Changes
Assignment: Classify the following as chemical or physical changes:
a) sugar dissolves in water
b) a steak is well cooked
c) the filament of a light bulb glows when an electric current flows through it
d) a piece of chalk is crushed
e) a plant grows taller
(a) Physical change: Only the arrangement of the particles is changed, and
sugar can be returned to solid form by boiling away the water.
(b) Chemical change: The cooked meat has changed colour and absorbed
heat and cannot be turned back to raw meat. Note that, although the
absorption of heat causes the chemical change, it is not in itself evidence of a
chemical change. Other observations are also needed.
(c) Physical change: The filament looks the same before the switch is
turned on and after it is turned off.
(d) Physical change: Only the arrangement of the particles is changed.
(e) Chemical change: The plant is producing new materials (leaves, stems,
flowers) as it grows.