Kinetic Particle Theory

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Self-study before class as homework (read from textbook): States of matter Matter can exist as a solid, liquid or gas. Different properties of solid, liquids or gas: Solid - fixed shape, fixed volume and cannot be compressed Liquid - not fixed shape, fixed volume and cannot be compressed Gas - not fixed shape, not fixed volume and can be compressed  Kinetic Particle Theory  The kinetic particle theory states that all matter is made up of tiny particles and that these particles are in constant, random motion. Solid State Particles are closely packed in an orderly pattern.  The particles are held together by strong forces of attraction. They are not able to move about freely. They only have enough kinetic energy to vibrate and rotate about their fixed positions. Hence, a solid has a fixed shape. A solid cannot be compressed as its particles are already very close to one another. Thus solids also have a fixed volume.  Liquid State More space between the particles as compared to a solid  The forces of attraction between the particles of a liquid are weaker than those in a solid. The particles of the liquid are not held in fixed positions. They are arranged in a disorderly manner and can move freely by sliding over one another. Hence, liquid does not have a fixed shape. The particles of a liquid have more kinetic energy than the particles of the same substance in the solid state.  The particles of a liquid are father away from one another than the particles in a solid. However, the particles of a liquid are still packed quite closely together. Hence, a liquid cannot be compressed and has a fixed volume. Gaseous state Particles are spread far apart from one another as the forces of attraction between the particles are very weak. Gases have a lot of kinetic energy and are not held in fixed positions. They can move about rapidly in any direction. Hence, a gas has no fixed shape. Particles of a gas have a lot more space between them as compared to those of liquids and solids. The larger space allows the gas to be easily compressed when pressure is applied. Hence, the gas can be compressed and has no fixed volume. Change of state Change of state is reversible.  Particles of matter are in constant motion. They have kinetic energy.  When a matter is heated or cooled, the heat taken in or given out causes the kinetic energy of the particles to change.  MELTING (solid to liquid) Heat energy is absorbed by the particles in the solid. The heat energy is converted to kinetic energy. The particles start to vibrate faster about their fixed positions. When the temperature is high enough, the vibrations become sufficient to overcome the attractive forces between them. The particles are no longer in their fixed positions. The particles slide over one another. The substance is now liquid. A heating curve shows how the temperature of a solid changes as it is heated to its melting point. FREEZING (liquid to solid) Energy is given out by the particles of the liquid. The particles lose kinetic energy and begin to move more slowly.When the temperature is low enough, the particles no longer have enough energy to move about freely. Some particles start to settle into fixed positions. All the particles settle into fixed positions. Particles can only vibrate about their fixed positions. The substance is now called a solid  A cooling curve shows how the temperature of a pure liquid changes as it is cooled to its freezing point. EVAPORATION (liquid to gas at temperature lower than boiling point) Evaporation occurs because some particles have enough energy to escape as a gas from the surface of the liquid. Volatile liquids: Liquids that evaporate quickly at room temperature. WHAT IS THE DIFFERENCE BETWEEN BOILING AND EVAPORATION? Boiling occurs only at boiling point whole evaporation occurs at temperatures below boiling point Boiling occurs throughout the liquid while evaporation occurs only at the surface of the liquid Boiling occurs rapidly whole evaporation occurs slowly. CONDENSATION (gas to liquid) Heat energy is given out during condensation. As the temperature drops, the gas particles lose energy and move more slowly. Eventually, the movement of the particles become slow enough for gas to change into a liquid. SUBLIMATION (solid to gas - without going through liquid state) Sublimation occurs because particles at the surface of the solid have enough energy to break away from the solid and escape as a gas (examples: iodine and ammonium chloride) DIFFUSION IN GASES  The process by which particles move freely to fill up any available space is called diffusion. When gases are evenly spread out, we say that a homogenous mixture is formed. Gas particles of different sizes diffuse at different rates. The smaller the particle is, the faster the gas can diffuse. Gas of different masses diffuse at different rates. The lighter the particles, the faster the gas can diffuse. In other words, gases with lower molecular masses diffuse faster than those with higher molecular masses. DIFFUSION IN LIQUIDS Diffusion is the movement of particles from a region of higher concentration to a region of lower concentration.

Important notes for AA in T1W9! MACRO-CONCEPT: MODELS  Note! Models are tentative (they will have to change when there are new ideas/findings) What is a scientific model? It is a representation, a prototype or replica of the object/phenomenon that could well explain its physical properties.  Phenomenon includes physical phenomenon like diffusion, dissolving, boiling, condensation, evaporation, melting, sublimation. Physical properties include volume, density, conductivity etc.  What are the assumptions for the Kinetic Particle Model?  Assumptions are valid statements to set the parameters for the model to work. Without the assumption, the principles of the model become invalid or irrelevant.  1. Particles are discrete and small. 2. Particles are in constant motion in randoom directions. 3. Particles possess kinetic energy. Forces of attraction between the particles  4. Heavier particles travel slower than lighter particles. 5. Particles do not stick to each other after collision (elastic collision) 6. Particles do not stick with the walls of container after collision and bounces back after collision with the walls of the container. 7. particles travel in a straight line.  8. Particles are small and discrete. 9. Temperature is an indication of the kinetic energy of the particles, not an indication of the heat added to the substance. What are the limitations of the Kinetic Particle Model?  *** look at the model! Some points may not be a limitation anymore, depending on the model Limitations are features of the model not aligned with the actual properties and are not able to illustrate the principles of the phenomenon.  1. Forces of attraction between particles are not seen in the model (only for static pictures but can be shown clearly on animation). 2. Movement of particles in terms of direction and speed may not be accurately captured on static picture but can be shown clearly on animation.  3. Distance between particles in model may not be scaled accurately to the actual distance between particles.  Note! The change of temperature is the change of kinetic energy. If the substance posses a lot of kinetic energy, the temperature of substance is high.  Comparing the KPT model to a rock concert Features similar to kinetic particle model: -       During concert, people are closely packed and jumping at fixed positions, just like particle in solid state, etc… -       When concert ends, people are moving disorderly sliding past each other but still closely packed, just like particles in liquid state, etc… **** State what happens at the concert and compare to properties of states of matter and KPT. Assumptions: -       People are large in numbers yet small in size relative to entire concert hall -       People do not stick to each other upon collision -       Each person possess kinetic energy -       Each person moves in constant random motion Limitations: -       People are of different sizes/masses unlike particles which are of the same size/mass of same substance -       There is no force of attraction between people unlike particles which consist strong forces of attraction between them -       People are not standing in ordered arrangement, unlike particles in solid state in ordered arrangement Chemical or physical changes Some changes are slow to take place Physical change No new substance formed Usually easily reversible May or may not involve heating  Some types of physical changes include: 1)grinding, tearing, cutting or shaping; 2) A change of state or phase from a solid to a liquid to a gas (melting ice; boiling water) Chemical change  New chemical substance(s) is/are formed  Usually irreversible (some chemical changes can be reversed under special conditions) Heat energy may be given off or absorbed Light energy may be given off or absorbed  Signs of a chemical change:   A change in colour  Production of a gas Formation of a precipitate from mixing solutions  Change of temperature  All the above must follow the formation of a new chemical substance. Note that it is not necessary for all the signs to be shown. Chemical Reactions A process in which new chemical substances are formed: reactants --> Products  New chemical substances formed due to rearrangement of atoms.  No atoms are created or destroyed, according to the Law of Constant Mass Types of Chemical Reactions 1. Combination (synthesis)  Two or more substances combine to form a new substance (eg. magnesium + oxygen --> Magnesium oxide) 2. Decomposition  A substance breaks down into two or more simpler substances (eg. calcium carbonate --> calcium oxide + carbon dioxide) 3. Combustion or burning  Combination of a substance with oxygen. Heat and light energy are given off. (eg. hydrocarbon + oxygen --> carbon dioxide + water) 4. Displacement Reaction  A chemical reaction with an atom/a group of atoms get replaced by another atom/group of atoms. (eg. hydrogen bromide + chlorine --> hydrogen chloride + bromine)  KPT All matter are made up of tiny discrete particles The tiny particles are in constant random motion  These particles in motions have kinetic energy  Higher the temperature, faster the movement of these particles  Solid model  Particles in solids are.. parcked close together in an orderly arrangement. Held together by strong forces of attraction Able to vibrate about the fixed positions but are free to move amongst each other Hence, solids have a fixed shape and volume. Solid cannot be compressed.  Liquid model Particles in liquid are... Packed quite close together but are slightly further apart than in solids. Not in an orderly arrangement  Held together bu strong forces of attraction (weaker than solids) Able to move throughout the liquid Hence, liquids have fixed volume but no fixed shapes. Liquids cannot be easily compressed. Gas model  Particles in gases are... Far apart from each other In a random arrangement Not held together by strong forces (negligible forces of attraction) Able to move freely in all directions Hence, gases have no fixed volumes and no fixed shapes. In addition, gases can be easily compressed. Melting Solid particles gain energy when heated Particles vibrate faster As temperature increases, vibration also increase Finally, particles are able to overcome the forces that hold them in their fixed positions.  Melting point: Temperature at which solid turns into liquid. Boiling Liquid particles gain energy when heated Particles move more quickly as temperature is increased Finally, partcles have sufficient energy to completely break the forces holding them together Particles are now able to move freely and apart.  Boiling point; temperature at which liquid turns into a gas Evaporation  Change of state of a liquid into its vapour at any temperature  Occurs below the boiling point of the liquid  Much slower than boiling Particles escape from the surface of the liquid to form a gas.  Condensation As the temperature drops, the gas particles lose energy to the surrounding and move more slowly Eventually, the movements Macroscopic vs Microscopic (Matter vs Particles)  Matter can feel hot or cold but not particles (Temperature is due to the speed of movement of particles) Gases can be compressed but the size of particles does not change (Distance between the particles of gas that changes not the size of particles.)  [Activity: Classify each of the following substances as either a solid, liquid or gas at 20ºC.] Petrol (melting point: -40, boiling point 62) --> Liquid Ammonia (melting point: -77, boiling point -34) --> Gaseous Copper (II) Chloride (melting point: 620, boiling point: 990) --> Solid Methane (melting point: -85, boiling point: -60) --> Gas Diffusion  Diffusion is the movement of substance from higher concentration to region of lower concentration.  Particles of one substance mingle with and move and spread through particles of another substance Mainly seen in gases and liquids. Bigger the mass, slower the rate  Higher the temperature, the faster the rate. Brownian motion   In 1827,  a botanist named Robert Brown, observed under a microscope that some dead pollen grains suspended in water were constantly moving randomly in all directions.