Matter in Our Surroundings
States of matter, evaporation, latent heat, and effect of temperature and pressure.
Chapter Overview
Temperature and pressure determine the state of matter. Heating increases kinetic energy of particles.
Matter exists in three states — solid, liquid, and gas — depending on interparticle forces and kinetic energy. This chapter covers characteristics of particles, changes of state, evaporation, and factors affecting it.
States of Matter
- Solid: definite shape and volume; particles vibrate in fixed positions
- Liquid: definite volume, no fixed shape; particles slide over each other
- Gas: no fixed shape or volume; particles move randomly at high speed
Change of State
Melting point
Temperature at which solid → liquid (e.g. ice 0°C)
Boiling point
Temperature at which liquid → gas (water 100°C at 1 atm)
Latent heat
Q = mL (L = specific latent heat)
Evaporation
- Surface phenomenon — particles with enough KE escape as vapour
- Increases with temperature, surface area, wind; decreases with humidity
- Causes cooling (e.g. sweat evaporation)
Solved Examples
Step-by-step solutions — read each step before checking the final answer.
Latent heat of fusion
How much heat to melt 2 kg ice at 0°C? (L_f = 334 kJ/kg)
- 1Q = mL = 2 × 334 kJ
- 2Q = 668 kJ
Answer
668 kJ
Evaporation cooling
Why does water in an earthen pot stay cool?
- 1Water seeps through pores
- 2Evaporation from outer surface
- 3Latent heat taken from water → cooling
Answer
Evaporation causes cooling
Key Points to Remember
- ✓ Particles of matter have spaces and are in constant motion
- ✓ Diffusion is faster in gases than liquids
- ✓ Sublimation: solid directly to gas (camphor, dry ice)
Exam Tips
- • Draw particle diagrams for three states
- • Distinguish evaporation from boiling
- • State SI units for heat and mass
Practice MCQs — Matter in Our Surroundings
Test your understanding with topic-wise multiple choice questions. Explanations appear after each answer.
Which state has maximum interparticle spaces?