Chapter 2 - Physical and Chemical changes Flashcards
What is a physical change?
A physical change is a change in which no new substances are formed and the chemical composition of the original substance remains the same , even though some of its physical properties such shape , colour , state etc . may change.
Characteristics of a physical change.
⁕No new substance is formed.
⁕There is no change in the chemical composition of the original substance.
⁕The change is temporary and it can be reversed by reversing the conditions.
⁕The change is only in the state , size , shape , colour , texture or smell of some or all substances that go through the physical change.
⁕There is no change in the mass of the substances involved in a physical change.
⁕There is usually no loss or gain of energy as a result of a physical change.
What is a chemical change?
A chemical change is a permanent change in which new substances are formed whose chemical composition and physical and chemical properties are different from those original substances.
Characteristics of a chemical change.
⁕New substance(s) is/are formed.
⁕The composition of the original substance completely changes.
⁕The change is permanent and irreversible.
⁕There is a change in the mass of the original substance.
⁕There is usually an exchange energy in a chemical change which means energy in the form of heat and light may be absorbed or rejected.
Why is burning of candle a chemical change?
when a candle is lighted , some of the molten wax first melts and turns into a fluid , and then burns to produce a flame. New substances CO₂ and water vapour are formed along with the evolution of heat and light energy. this shows a chemical change.
