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4. States of Matter I The gaseous state: (i) Ideal gas behaviour and deviations from it (II) pV = nRT and its use in determining a value for Mr II The liquid state The kinetic concept of the liquid state and simple kinetic-molecular descriptions of changes of state III The solid state Lattice structures

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Learning Outcomes Candidates should be able to: (a)state the basic assumptions of the kinetic theory as applied to an ideal gas (b) explain qualitatively in terms of intermolecular forces and molecular size: (i) the conditions necessary for a gas to approach ideal behaviour (ii) the limitations of ideality at very high pressures and very low temperatures (c) state and use the general gas equation pV = nRT in calculations, including the determination of Mr (d) *describe, using a kinetic-molecular model, the liquid state; melting; vaporisation and vapour pressure (e) *describe, in simple terms, the lattice structure of a crystalline solid which is: (i) ionic, as in sodium chloride, magnesium oxide (ii) simple molecular, as in iodine (iii) giant molecular, as in graphite; diamond; silicon(IV) oxide (iv) hydrogen-bonded, as in ice (v) metallic, as in copper [the concept of the unit cell is not required]

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(f) explain the strength, high melting point and electrical insulating properties of ceramics in terms of their giant molecular structure (g) relate the uses of ceramics, based on magnesium oxide, aluminium oxide and silicon(IV) oxide, to their properties (suitable examples include furnace linings; electrical insulators; glass; crockery) (h) describe and interpret the uses of the metals aluminium, including its alloys, and copper, including brass, in terms of their physical properties (i)understand that materials are a finite resource and the importance of recycling processes (j) outline the importance of hydrogen bonding to the physical properties of substances, including ice and water (k) suggest from quoted physical data the type of structure and bonding present in a substance

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Avogadros law: Equal volumes of any gas measured at the same temperature and pressure contain the same numbers of particles (atoms and molecules In order for volumes of gases to be comparable, they must be measured under the same conditions of temperature and pressure. Alternatively the volumes at the required temperature can be worked out using the Ideal Gas Equation.

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Remember Boyles Law: PV = constant Charles Law: V = constant T

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PV = constant (for a fixed mass of gas) T If we take 1 mole of gas the constant is given the symbol R and is called the gas constant, and for n moles of gas we have PV = nRT R is a constant, 8.314 KJ -1 mol -1 P, pressure must be in Pascals, Pa; V, volume must be in m 3 (1m 3 = 10 6 cm 3 = 10 3 dm 3 ), T, temperature must be in Kelvin, K

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Kinetic theory is an attempt to explain the observed properties of gases - The particles are moving randomly - We can neglect the volume of the particles themselves in comparison to the total volume of the gas - The particles do not attract one another - The average kinetic energy of the particles is proportional to the temperature of the gas - No energy is lost in collisions between particles - Bombardment of the walls of the container explains pressure and increasing temperature makes them hit walls harder, so pressure increases

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Deviations from Ideal Gas Behaviour When gases are put under high pressure or cooled down the gas molecules get closer together (or move slower at lower temperatures) and they become attracted to each other using intermolecular forces and start to form a liquid. So there are no gases at 0 K!

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What volume is needed to store 0.050 moles of helium gas at 202.6kPa and 400K? What pressure will be exerted by 20.16g hydrogen gas in a 7.5L cylinder at 20 o C? A 50L cylinder is filled with argon gas to a pressure of 10130.0kPa at 30 o C. How many moles of argon gas are in the cylinder? To what temperature does a 250mL cylinder containing 0.40g helium gas need to be cooled in order for the pressure to be 253.25kPa?

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What volume is needed to store 0.050 moles of helium gas at 202.6kPa and 400K? PV = nRT P = 202.6 kPa n = 0.050 mol T = 400K V = ? L R = 8.314 J K -1 mol -1 202.6V=0.050x8.314x400 202.6 V = 166.28 V = 166.28 ÷ 202.6 V = 0.821 L (821mL)

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What pressure will be exerted by 20.16g hydrogen gas in a 7.5L cylinder at 20 o C? PV = nRT P = ? kPa V = 7.5L n = mass ÷ MM mass=20.16g MM(H 2 )=2x1.008=2.016g/mol n=20.16 ÷ 2.016=10mol T=20o=20+273=293K R = 8.314 J K -1 mol -1 Px7.5=10x8.314x293 Px7.5 = 24360.02 P = 24360.02 ÷ 7.5 = 3248kPa

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A 50L cylinder is filled with argon gas to a pressure of 10130.0kPa at 30oC. How many moles of argon gas are in the cylinder? PV = nRT P = 10130.0kPa V = 50L n = ? mol R = 8.314 J K -1 mol -1 T=30 o C=30+273=303K 10130.0x50=nx8.314x303 506500=nx2519.142 n=506500 ÷ 2519.142=201.1mol

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To what temperature does a 250mL cylinder containing 0.40g helium gas need to be cooled in order for the pressure to be 253.25kPa? PV = nRT P = 253.25kPa V=250mL=250 ÷ 1000=0.250L n=mass ÷ MM mass=0.40g MM(He)=4.003g/mol n=0.40 ÷ 4.003=0.10mol R = 8.314 J K mol -1 T = ? K 253.25x0.250=0.10x8.314xT 63.3125 = 0.8314xT T=63.3125 ÷ 0.8314=76.15K

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Calculations

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