[PHY] Chapter 8 - Kinetic Model of Matter

DARRELL ER (COPYRIGHTED) © TOPIC 8: KINETIC MODEL OF MATTER DARRELL ER (COPYRIGHTED) ©

CHAPTER ANALYSIS THE ABOUT MASTERY EXAM WEIGHTAGE DARRELL ER (COPYRIGHTED) ©

KINETIC MODEL OF MATTER SOLID, LIQUID, GAS TEMPERATURE & MOTION OF MOLECULES KEY CONCEPT DARRELL ER (COPYRIGHTED) ©

KINETIC MODEL OF MATTER KINETIC MODEL OF MATTER DARRELL ER (COPYRIGHTED) © Physical properties Solid Liquid Gas Diagram Arrangeme nt of particles Packed close together; orderly arrangement Packed loosely together; disorderly arrangement Far apart; random arrangement Movement of particles Vibrate about fixed position Slide over one another Moves randomly at high speed Shape & Volume Fixed shape & fixed Volume No fixed shape but has fixed volume No fixed shape & no fixed volume (can be compressed) Space between molecules Very little Little space (more than solid) Large space Forces between particles Very strong attraction Strong attraction (weaker than solid) Weak attraction Density Very high – particles are close together High – particles are close together Very low – particles are far apart

BROWNIAN MOTION Brownian motion is defined as the constant random movement of smoke particles suspended in a fluid (liquid or gas) due to the uneven bombardment of the suspended particles by the air molecules. Smoke particles movement Smoke particles are observed to move continuously and randomly as they are being hit by unseen, fast-moving air molecules. The reflection of light off the surfaces of the smoke particles appears as bright specks of lights to observers. BROWNIAN MOTION DARRELL ER (COPYRIGHTED) ©

PRESSURE, VOLUME & TEMPERATURE OF GAS For a gas inside a container, the gaseous molecules will collide against the container wall and exert a force per unit area, giving rise to gaseous pressure. A higher frequency of collision will also result in greater force exerted and hence increasing the pressure as well. Formula: PV = nRT Can be simplified to, PV ∝ T RELATIONSHIP OF GAS DARRELL ER (COPYRIGHTED) ©

Pressure ∝ Temperature For a fixed mass of gas at constant volume, when temperature is higher, thermal energy is transferred to the molecules and gaseous particles move faster. This increases both the frequency of collision against the wall and the force exerted by each gaseous particle. Pressure will hence increase. DARRELL ER (COPYRIGHTED) © RELATIONSHIP OF GAS

Pressure ∝ 1/ volume For a fixed mass of gas at constant temperature, average speed of the molecules remains the same. Decreasing the volume of the container means that the number of gas molecules per unit volume in the container is increased. As number of molecules hitting the wall per unit time also increases, pressure increases. Boyle’s Law P1 x V1 = P2 x V2 DARRELL ER (COPYRIGHTED) © RELATIONSHIP OF GAS

Volume ∝ Temperature If pressure is constant, an increase in temperature would increase the volume of the container. When temperature is higher, thermal energy is transferred to the molecules and gaseous particles move faster. This increases both the frequency of collision against the wall and the force exerted by each gaseous particle. Pressure will hence increase. In order to reduce the frequency of collision in order to maintain a constant pressure, volume will increase to reduce the number of particles per unit volume and hence reducing the number of collisions, which helps to maintain pressure at constant value. DARRELL ER (COPYRIGHTED) © RELATIONSHIP OF GAS

TEMPERATURE ∝ MOTION OF MOLECULE When temperature is higher, thermal energy is transferred to the molecules and gaseous particles gain kinetic energy. This cause the molecules to move faster. This increases both the frequency of collision against the wall and the force exerted by each gaseous particle. Since pressure is force per unit area, pressure will hence increase. RELATIONSHIP OF TEMPERATURE & MOTION OF MOLECULES DARRELL ER (COPYRIGHTED) ©