Review the key concepts, formulae, and examples before starting your quiz.
πConcepts
A Physical Change is a temporary change in which no new substance is formed, and the chemical composition of the original substance remains the same. Example: Melting of ice ().
A Chemical Change is a permanent change in which a new substance with different properties is formed. It is usually irreversible. Example: Burning of Magnesium ().
Characteristics of Physical Changes: Reversible, no change in mass (of the specific substance), and no net absorption or release of energy in large amounts.
Characteristics of Chemical Changes: Irreversible, change in the mass of individual substances, and significant energy changes (Exothermic or Endothermic).
Law of Conservation of Mass: In any chemical change, the total mass of the reactants is equal to the total mass of the products ().
Exothermic Reactions are chemical changes that release heat energy to the surroundings, such as the respiration process ().
Endothermic Reactions are chemical changes that absorb heat energy from the surroundings, such as photosynthesis ().
πFormulae
π‘Examples
Problem 1:
Explain whether the burning of a candle is a physical or chemical change.
Solution:
It is both a Physical and Chemical change.
Explanation:
The melting of wax is a physical change because it can be solidified back into wax (). The burning of the wick and wax vapor to produce and is a chemical change because new substances are formed and it is irreversible.
Problem 2:
What is observed when an iron nail () is placed in a blue colored Copper Sulphate () solution?
Solution:
Explanation:
This is a chemical change called a displacement reaction. The blue color of fades and turns light green due to the formation of Ferrous Sulphate (), and a brown deposit of Copper () is seen on the nail.
Problem 3:
Identify the type of change: .
Solution:
Physical Change (Sublimation).
Explanation:
Sublimation of Ammonium Chloride () is a physical change because it only involves a change in state from solid to gas and can be reversed by cooling (deposition) without changing the chemical identity.