Grade 10 Chemistry Knowledge area Chemical change Physical

Grade 10 Chemistry Knowledge area: Chemical change

Physical and chemical change 1. 1 Separation of particles 1. 1. 1 Physical change • Types of changes: 1. State change 2. Change of shape 3. Colour change • Energy is required. Relatively small amounts of energy are necessary These are mainly reversible reactions. A change in shape is not always reversible.

Physical and chemical change 1. 1 Change of condition (state) Examples • Ice melts and forms water. • Water evaporates and forms water vapour. • Water freezes and forms ice. • Water vapour condenses and forms water. Sublimation is a process whereby a solid changes directly into a gas. Definition

Physical and chemical change Examples Dry ice (CO 2 solid) becomes CO 2(g). Quick facts Dry ice is typically used in ice-cream carts to keep the ice-cream iced. When it sublimates, it does not change into a liquid, which would make a mess.

Physical and chemical change Below is a table of the characteristics of state change that focuses particularly on water: SOLID: ICE LIQUID: WATER GAS: WATER VAPOUR • Spaces between particles (ice molecules) are larger than expected due to hydrogen bonds. • Orderly arrangement of particles • Particles only vibrate. • Strong forces between particles • Small spaces between particles (water molecules) • Particles move in a random, but restricted fashion. • Collisions between particles occur. • Weaker forces between particles • Big empty spaces between particles (vapour molecules) • Particles move fast. • High speed collisions occur between particles. • Movement is random. • Very weak/no forces between particles

Physical and chemical change SOLID: ICE LIQUID: WATER Just before melting: • Particles move faster. • Particles further apart • More intense collisions due to higher speed. During state change: • Spaces between particles increase. • Forces between particles weaken. • Arrangement is less orderly. melting GAS: WATER VAPOUR Just before evaporation: • Particles move very quickly. • Particles are far apart. • Intense collisions at high speeds During state change: • Spaces between particles are huge. • Forces between particles are weak. • Arrangement is random. evaporation

Physical and chemical change SOLID: ICE LIQUID: WATER freezing Just before freezing: • Particles move very slowly. • Particles are close together. During state change: • Very small spaces between particles • Forces between particles are very strong. • More orderly arrangement of particles GAS: WATER VAPOUR condensation Just before condensation: • Particles move slower. • No longer far apart • Collisions are less intense. During state change: • Spaces between particles decrease. • Forces between particles strengthen. • Arrangement is more orderly. No kinetic energy change occurs during this state change.