Physical and Chemical Changes

Vocabulary flashcards defining physical and chemical changes, their properties, and specific experimental observations based on the lecture transcript.

Physical Change

A change which alters some specific property of matter without any change in the composition of its molecules.

Chemical Change

A change which alters the specific properties of a substance by bringing about a change in its molecular composition, followed by a change in its state.

Zinc Oxide Heating

A temporary physical change where $2\,\text{g}$ of white zinc oxide powder strongly heated for $2\,\text{minutes}$ turns yellow, and returns to white upon cooling.

Lead Oxide Heating

A temporary physical change where yellow lead oxide powder changes to a reddish brown colour on heating and changes back to yellow upon cooling.

Dissolution and Evaporation of Common Salt

A physical change where common salt dissolved in $50\,\text{cm}^3$ of water leaves behind the original mass of salt (e.g., $15\,\text{g}$) after water evaporates.

Heating of Platinum Wire

A temporary physical change where a short length of platinum or nichrome wire held in a non-luminous Bunsen flame becomes red hot and regains its original colour upon cooling.

Magnetisation of Iron Wire

A temporary physical change where a bicycle spoke becomes a magnet after being rubbed with a permanent bar magnet, and loses its magnetism after being struck against a table $50\,\text{times}$.

Magnesium Oxide

The white ash with entirely different properties formed when a $5\,\text{cm}$ magnesium ribbon burns in a non-luminous flame for about $2\,\text{minutes}$, releasing heat and light.

Burning of a Candle

A permanent chemical change in which candle wax burns to give off heat and light energy, producing carbon dioxide gas and water vapour.

Decomposition of Mercuric Oxide

A permanent chemical change where $2\,\text{g}$ of red mercuric oxide turns black on strong heating and decomposes into oxygen gas (which lights a glowing splint) and silvery droplets of mercury.

Decomposition of Sugar

A permanent chemical change where $2\,\text{g}$ of sugar melts, turns brown, gives off steam, and leaves behind a black residue of charcoal (carbon).

Characteristics of Physical Changes

Properties defining physical changes: no new substance is formed, changes are generally reversible, there is no change in weight, and only a little heat (if any) is absorbed or given off.

Characteristics of Chemical Changes

Properties defining chemical changes: permanent in nature, irreversible, forms new substances with entirely new properties, alters molecular composition, and evolves heat and light energy.