Kinetic Theory of Matter PDF

‘Kinetic’ Theory of Matter What is matter? How do we define matter? What is the physics behind matter? 1  Kinetic theory of matter Kinetic theory  based on the idea that particles of matter are always in motion, above absolute zero K...

‘Kinetic’ Theory of Matter What is matter? How do we define matter? What is the physics behind matter? 1  Kinetic theory of matter Kinetic theory  based on the idea that particles of matter are always in motion, above absolute zero K ( = -273.15oC). Explains the properties of solids, liquids, and gases in terms of: the energy of the atoms and forces that act between atoms. 2  States of Matter Matter something that contains : atoms or molecules is the normal state we Material recognize this matter as. Solid Liquid Gas/Vapour Ice, water and steam are three different states of matter of the same material. 3  State of Matter: Plasma Plasma = when high energy added to a gas it disassociates to give a gas containing ionized particles = possess +ve ions and free -ve electrons. Heating a gas may ionize its molecules or atoms, thus turning it into a plasma. Strong electromagnetic fields applied with a laser or microwave generator also creates plasma. Lightning is an example of plasma present at Earth's surface. Typically, lightning The presence of a number of charge carriers makes the discharges 30,000 amperes at up to 100 plasma electrically conductive so that it responds million volts, and emits light, radio waves, X- strongly to electromagnetic fields. Plasma, therefore, has rays and even gamma rays. Plasma temperatures in lightning can approach properties quite unlike those of solids, liquids, or gases ~28,000 kelvin. and is considered a distinct state of matter. Like gas, plasma does not have a definite shape or a definite volume unless enclosed in a container. Unlike gas, forms structures such as filaments and beams under the influence of a electro-magnetic field. Some common plasmas are stars, lightening and the excited gas in neon signs & plasma TV’s. 4  What is Gas? Properties that define a gas state:  No fixed shape and no fixed volume  Assumes the shape and volume of its container  Highly compressible  Deforms/ Flows easily Distance between molecules  The molecules are far apart- with very little attraction between them.  A gas can be compressed because the molecules are far apart and there is a lot of space between them. 5  Gas Laws ‘Kinetic molecular theory’ is used to explain gas behavior. Every day observation of gas behavior: “sealed bag of potato crisps bulges at its seams when placed in a sunny window “ Why does this happen? Kinetic theory can explain this and other interesting gas behaviors.  Kinetic theory of gases 1. Gas consists of hard, spherical particles, with the following properties:-  particles are so small in relation to the distances between them that their individual volumes can be assumed to be insignificant.  the large relative distances between the particles means that there is considerable empty space between the particles. 2.Gas particles move rapidly in straight paths, independently and in constant random motion. They therefore possess kinetic energy, (energy of motion). 3.No attractive or repulsive forces exist between the particles. Kinetic energy overcomes attractive forces between atoms. 4. Collisions between gas particles and between particles and container walls are elastic collisions. Elastic collision - there is no net loss of kinetic energy  Boyle’s Law The Pressure – Volume Relationship Boyle’s Law Consider the effect of pressure on the 1627-1691 volume of a contained gas while the “temperature remains constant.” Boyle’s law states that: “for a given mass of gas, at constant temperature, the volume of the gas varies inversely with pressure.” When pressure increases, then volume is reduced. P Similarly, pressure reduces with increase in volume:  Practical Examples Think about what happens to your bicycle tyres in the winter As the temperature decreases the tyres deflate = less volume. This also happens if you take a balloon outside on a cold day ( the kinetic energy of the gas reduces, so does the pressure , so the container = balloon, is less stretched to contain the gas = less volume.  Gay-Lussac’s Law The Pressure - Temperature Relationship Joseph Gay-Lussac (1778-1850), French chemist Gay-Lussac’s law states: “the pressure of a fixed mass of gas is directly proportional to the Kelvin temperature if the volume remains constant.”  The “Amount” of a Gas We have looked at changing : pressure, volume, and temperature. There is a fourth variable : the amount of gas in the system. The ‘amount’ of a chemical substance is expressed in terms of the number of moles, n. Unit amount = mole ( sometimes written as mol) *** a mole of a material is simply the atomic weight, (if it is an element), or molecular weight (relative molecular mass if a molecule) expressed as grams. Example , nitrogen atomic mass 14.007 a.m.u 1 mole of a nitrogen gas ‘molecule’ = 2 x 14.007 ~ 28 g.  AVOGADRO’S HYPOTHESIS The number of moles of gas is directly proportional to the number of particles The ‘particles’ that make up different gases are not the same size. For example: Chlorine molecules have a large number of electrons, protons and neutrons. They have bigger atomic radii, and exist as two chlorine atoms bonded via covalent bonds. They therefore occupy more volume than a helium ‘molecule’ which has only two protons+ 2 neutron and two electrons. Early scientists assumed, logically, that a collection of larger molecules would occupy a larger volume than the same collection of an equal number of small molecules.  AVOGADRO’S HYPOTHESIS “Equal volumes of gases at the same temperature and pressure contain equal numbers of particles”. Think about this !!! Avogadro suggests that a room of say, 4 m x 4 m x 3m in volume would need the same number of golf balls to fill it as the number of basketballs! Avogadro realized that there would be large expanses of space between the particles since they were so small and far apart. He suggested that ‘1 mole’ of any gas, irrespective of its atom size, would occupy 22.4 L ( at STP). Recall: a mole = atomic ( or molecular) mass expressed in gram. 1 mol of : Carbon = 12.0 g, 1 mol of Nitrogen = N = 14g.  What is a Liquid? Properties that define a liquid state:  Made up of clusters with molecules ( or atoms if molten metal) which are slightly further apart compared to solids.  Fixed volume but no fixed shape  Assumes the shape of the container which it occupies  Deformed /flows easily ( attractive forces between molecules is weaker) Distance between molecules  The molecules are not arranged in a regular pattern and are slightly further apart than in solids.  Liquids cannot be compressed as the molecules are relatively close together and there is little space between them. Note: only one metal exists as a liquid at room temperature – Mercury. All other liquids are composed of molecules i.e. H2O, C6 H6 , liquid N2, liquid CO2 14  What is a Solid? Define a ‘solid’  Fixed shape and fixed volume  Not compressible  Does not flow Distance between atoms (metals) or molecules (ceramics, wood, polymers, etc)  Atoms or molecules are arranged close together in a regular pattern.  Solids cannot be compressed because the atoms or molecules are already arranged as close together as physically possible = there is little space between them to squash any closer together. Note: metals generally consist of a 3d array of ‘single atoms’ while other solid materials (ceramics, wood, polymers, etc) are composed of ‘molecules.’ 15 In Solids:  There are balanced forces between the atoms. These forces hold them in fixed positions.  The atoms can only vibrate about their fixed positions alternately attracting and repelling one another – like oscillating magnetic poles, or attached via minute, invisible springs. Amplitude of oscillation ~ 10-12 m and frequency 1013 Hz  The strong attractive forces prevent the atoms from leaving their positions while the repulsive forces act when they are too close to each other to prevent them from colliding. This explains why a solid has a fixed shape and a fixed volume.  When a solid is ‘heated’, the atoms gain energy and vibrate even more vigorously. The separation between atoms increases slightly and the solid expands. More energy ( heat) = increased vibration 16 Summary states of matter: almost none 17  Kinetic Model = associated with the energy content of matter The kinetic theory of matter states that all matter is made up of a large number of atoms or molecules which are in continuous motion. The motion in solids is indiscernable – vibration, whereas motion in gas is vigorous and visible seen via Brownian motion – air molecules striking particles of smoke. When temperature increases, thermal energy is transferred to the molecules and the molecules gain kinetic energy ( ½mv2). Hence the molecules move faster - temperature of liquid thermometer = greater vibration = expansion of liquid - ‘warm air’ on summers day – molecules moving faster and striking our skin and transfer some of the kinetic energy to our bodies = we gain energy and feel warmer. 18 Adding/removing energy gives a change in state of matter 19  Phase changes of matter when we apply energy (heat). Heat energy absorbed exactly So we are adding energy balanced by energy to overcome but the temperature does attractive forces holding atoms not rise! and molecules in fixed position in the solid. Endothermic = needs heat in 20  What happens to matter when we remove energy? ?? So we are taking energy out but the temperature does not decrease! Exothermic – gives heat out Kinetic Model of Matter 21  Changes of state: Evaporation v’s Boiling 22 Test your understanding of changes of state 23  Particle Theory All matter consists of many, very small ………………. The particles are in a continual state of ………………….. The degree to which the particles move is determined by the amount of …………………..they have. The particles might be ……………, ………………or …….  Particle Theory All matter consists of many, very small particles. The particles are in a continual state of motion. The degree to which the particles move is determined by the amount of energy they have. The particles might be atoms, molecules or ions.  Describe the three states of matter in SOLID LIQUID GAS terms of their particles: MOTION FORCES ENERGY Consider each of the SOLID LIQUID GAS three states of matter in terms of their particles. Rapid random motion. Rapid random Vibrate about fixed Slide over each other. motion. MOTION positions Particles fill Take the shape of container. container. Weak forces of Very strong attraction and Strong forces of attraction FORCES repulsion. and repulsion. attraction and repulsion. Large amounts of ENERGY Little energy. Intermediate energy. energy.