Definitions [13]
Define a slow change.
Changes which take place over a long period of time (hours/days/months/years) are known as slow changes.
Define physical change. Give two examples for the above changes.
Physical change: A temporary change in which no new substance is formed, the composition of substance remains the same, though its state, shape and size may change.
Example of physical change:
- Change of water into its vapours.
- Heating of iron rod.
Define a chemical change. Give two examples of the above changes.
A permanent change in which new substances are formed whose composition and properties are completely different from those of the original
substances.
Chemical change:
(i) Burning of wood.
(ii) Breathing.
Define Triple point.
The triple point of water is that point where water in a solid, liquid and gas state co-exists in equilibrium and this occurs only at a unique temperature and a pressure.
The process of change from one state to another at a constant temperature is called the change of phase.
OR
A transition from one state of matter (solid, liquid, or gas) to another is called change of state.
Define Sublimation.
Sublimation is the process in which a solid changes directly into a gas on heating, without passing through the liquid state.
Explain the term Melting Point.
It can be defined as the fixed temperature at which a solid start changing to its liquid state is Melting Point
Explain the term Melting.
The physical process that results in the transition of a substance from the solid-state to the liquid state on heating at a fixed temperature is called Melting.
Define latent heat of fusion?
Heat energy is absorbed by a solid during melting and an equal amount of heat energy ‘ is liberated by the liquid during freezing, without any temperature change. It is called the latent heat of fusion.
Define the following:
Melting or fusion:
Melting or fusion: The process in which a solid is converted to a liquid by absorbing heat is called melting or fusion.
The change from liquid to gas (or vapour) phase on absorption of heat at a constant temperature, is called vaporisation.
The particular temperature at which vaporisation occurs is called the boiling point of liquid.
The change from vapour to liquid phase on liberation of heat at a constant temperature is called condensation (or liquefaction) and the particular temperature at which the condensation occurs is called the condensation point of vapour.
Key Points
- A change of state occurs when heat exchange causes a substance to transition between solid, liquid, and gas phases.
- Temperature remains constant during a phase change because heat energy changes molecular arrangement (potential energy), not molecular speed (kinetic energy).
- The heating curve has flat plateaus at the melting point (0 °C) and boiling point (100 °C) for water, with rising slopes in between.
Concepts [14]
- Changes-Physical and Chemical
- Classification of Change: Slow and Fast Changes
- Classification of Change: Natural and Man-made Changes
- Classification of Change: Periodic and Non-periodic Changes
- Classification of Change: Desirable and Undesirable Changes
- Classification of Change: Reversible and Irreversible Changes
- Classification of Change: Physical Changes
- Change of State
- Concept of Melting (Fusion)
- Vaporisation or Boiling
- Concept of Freezing (Solidification)
- Concept of Condensation (Liquefaction)
- Concept of Evaporation
- Indicators of a Chemical Change (Chemical Reaction)
