Matter and its importance / Jirim dan kepentingannya
Matter and its importance (Jirim dan kepentingannya) tests whether you can explain observable behaviour - compression, diffusion, melting and boiling - using the kinetic particle theory rather than description alone. SPM asks you to link particle arrangement, particle movement and forces to the properties of solids, liquids and gases, then apply that model to changes of state and everyday separation or purification contexts.
Core model
- Solid: particles closely packed, vibrate about fixed positions; fixed shape and volume; cannot be compressed.
- Liquid: particles close but irregular, slide past one another; fixed volume, takes container shape.
- Gas: particles far apart, move randomly at high speed; fills container, compressible. During a change of state, energy changes particle spacing and movement, not particle size or identity. Temperature stays constant at melting and boiling because absorbed heat is used to overcome attractive forces between particles, not to raise kinetic energy.
Worked example
A heating curve for ice at −10 °C shows a rise to 0 °C, a flat line at 0 °C, then a rise to 100 °C, then another flat line. Explain both plateaus. At 0 °C, ice melts: energy breaks the rigid lattice arrangement, allowing particles to slide; temperature does not rise until all ice has melted. At 100 °C, water boils: energy separates liquid particles into gas; again temperature is constant until vaporisation is complete. The length of each plateau depends on mass and the energy needed for the change of state, not on the final temperature.
Traps
Do not say particles expand when a gas is heated; they move faster and collide more forcefully, and spacing increases. Particles do not melt. Impurities usually lower melting point and raise boiling point. Diffusion is faster for lower-mass gas molecules at the same temperature, not because they are smaller in volume.