EP3_1A N5 Chemical Formula – Identifying Chemical & Physical Changes

SUMMARY

Changes of substances can be classified as physical or chemical. The key difference between the two is that for a chemical change a new substance is ALWAYS produced.

Signs of a chemical reaction:

• Color Change.
• Change of Temperature [energy change].
• Evolution of a gas (formation of bubbles)
• Precipitate (formation of a solid after two solutions are mixed, mixture would turn cloudy)

For physical change a change of state or shape occurs, but crucially, no new substance is formed.

• Change in size or shape.
• Change in state of matter (melting/ freezing boiling/ condensing)*.
• Reversible.
• No new substance formed!

* Ice, water and steam (or vapour) are chemically the same compound, H₂O, but just in solid, liquid or gas state.  As ice melts or water boils, it is still H₂O.  The liquid water can be refrozen to form ice.

NOW CHECK YOUR ANSWERS