CIE iGCSE Co-ordinated Sciences-P2.2.1 Thermal expansion of solids, liquids and gases- Study Notes- New Syllabus
CIE iGCSE Co-ordinated Sciences-P2.2.1 Thermal expansion of solids, liquids and gases – Study Notes
CIE iGCSE Co-ordinated Sciences-P2.2.1 Thermal expansion of solids, liquids and gases – Study Notes -CIE iGCSE Co-ordinated Sciences – per latest Syllabus.
Key Concepts:
Core
- Describe, qualitatively, the thermal expansion of solids, liquids and gases at constant pressure
Supplement
- Explain some of the everyday applications and consequences of thermal expansion
CIE iGCSE Co-Ordinated Sciences-Concise Summary Notes- All Topics
Thermal Expansion of Matter (at Constant Pressure)
Thermal expansion is the increase in size or volume of a substance when its temperature is raised at constant pressure, due to increased particle motion.
1. Solids
- Particles in solids are in a fixed lattice and vibrate about their mean positions.
- Heating increases the vibration amplitude of particles.
- Particles push slightly further apart → the solid expands slightly in length, area, or volume.
- Expansion is generally small and uniform, because particles are strongly bound.
Example: Metal rails expand in summer → expansion gaps are provided.
2. Liquids
- Particles are close but can slide past each other.
- Heating increases particle speed and average separation.
- Liquid volume increases more noticeably than solids because particles are less constrained.
Example: Thermometer liquids (mercury or alcohol) rise in the tube when heated.
3. Gases
- Particles are far apart and move freely.
- Heating increases particle kinetic energy → particles move faster → collisions with container walls are more frequent and energetic.
- At constant pressure, the gas expands greatly to occupy a larger volume.
Example: Hot air in a balloon → balloon inflates as air expands.
Key Concept:
- All substances expand on heating, but the degree depends on the strength of forces between particles and freedom of movement.
- Solids: very small expansion. Liquids: moderate expansion. Gases: very large expansion.
- Thermal expansion occurs because heating increases partbicle motion, increasing average separation between particles.
Summary Table
| State | Particle Arrangement | Effect of Heating | Observation |
|---|---|---|---|
| Solid | Fixed lattice | Particles vibrate more → slightly further apart | Small expansion in length/volume |
| Liquid | Close but irregular | Particles move faster → average separation increases | Moderate increase in volume |
| Gas | Far apart, random motion | Particles move faster → collisions push walls outward | Large increase in volume |
Example :
A metal bridge expands on a hot day. Explain why this happens using the particle model.
▶️ Answer/Explanation
Heating increases vibration of metal atoms → particles move slightly further apart → bridge expands in length.
Example :
Mercury in a thermometer rises when heated. Explain in terms of particle motion.
▶️ Answer/Explanation
Heating increases kinetic energy of mercury atoms → particles move faster and slightly further apart → volume of liquid increases → mercury rises in the tube.
Example :
A hot air balloon rises when the air inside it is heated. Explain this phenomenon using the particle model and thermal expansion.
▶️ Answer/Explanation
Step 1: Heating the air increases the kinetic energy of air particles → particles move faster.
Step 2: Particles move further apart at constant pressure → the air inside the balloon expands → density decreases.
Step 3: The density of hot air becomes less than the cooler outside air → buoyant force lifts the balloon.
Final Answer: The balloon rises because heating increases particle motion, expands the air, and reduces its density, producing lift.
Everyday Applications and Consequences of Thermal Expansion
When substances are heated, their particles move faster and on average are further apart. This causes solids, liquids, and gases to expand, which has both practical applications and sometimes undesirable consequences.
1. Solids
- Railway Tracks: Rails expand in hot weather → small gaps (expansion joints) are provided to prevent bending or buckling.
- Bridges: Metal and concrete bridges expand → expansion joints allow safe movement.
- Thermometers (solid parts): Some bimetallic strips in thermometers bend when heated due to differential expansion of metals → indicates temperature.
- Consequence: If expansion is not allowed for, solid structures may deform or crack.
2. Liquids
- Thermometers: Mercury or alcohol rises in the tube when heated → used to measure temperature accurately.
- Liquid-filled containers: Hot liquids may overflow if there is no space for expansion.
- Consequence: Spillage or container rupture if liquid expands too much without allowance.
3. Gases
- Hot Air Balloons: Heating the air decreases its density → balloon rises.
- Internal Combustion Engines: Gases expand in cylinders → perform work on pistons.
- Pressure Cookers: Gases inside increase pressure as temperature rises → cooks food faster.
- Consequence: Uncontrolled expansion can lead to bursting containers if not properly managed.
Example :
Why do railway tracks have small gaps between them in summer?
▶️ Answer/Explanation
Heating causes the metal rails to expand as particle vibrations increase. The small gaps allow this expansion without bending or buckling the tracks.
Example :
A metal lid is stuck on a glass jar. Explain how you can use thermal expansion to open the lid, and why this works in terms of particle motion.
▶️ Answer/Explanation
Step 1: Heat the metal lid (e.g., run under hot water).
Step 2: Heating increases the vibration of metal atoms → particles move slightly further apart → the lid expands.
Step 3: The glass jar expands very little because solids expand differently depending on material → the lid loosens relative to the jar.
Final Answer: The lid can now be unscrewed easily because thermal expansion of metal increased the lid’s size, reducing friction with the jar.