SUPPLEMENTARY TOPIC 2: more about gases.

Transcription

1 SUPPLEMENTARY TOPIC 2: mre abut gases. Behaviur f gases. Frm the kinetic mlecular thery (Supplementary Tpic 1) the mlecules f a gas are, n average, relatively far apart and in cnstant mtin in straight lines between cllisins, displaying cnsiderable rapid translatinal mtin. When the mlecules cllide, they rebund with n lss f energy. Als accrding t this mdel, cllisins f these fast-mving mlecules with the walls f the cntainer are the cause f pressure. In this Tpic, prperties f gases are further examined with regard t their respnse t pressure applied and t temperature, their slubility in water and their mlar vlumes. Atmspheric pressure. At sea level, the atmsphere f earth causes a pressure f 1.0 kg t be exerted n 2 each square centimetre f any bject (written as 1.0 kg cm. ). We are blivius t this pressure, just as a fish is nt aware f the much larger pressures t which it is subjected in the sea. Withut that cnstant pressure, the human bdy cannt functin prperly. Fr example, the actin f the lungs in breathing depends n air pressure causing fresh air t flw int the lungs when muscles expand the rib cage. In space, a persn nt maintained at atmspheric pressure by a space suit wuld experience the biling f all water in his bdy at bdy temperature due t the vacuum f space. Rapid travel up r dwn a steep hill may cause pressure imbalance n either side f the ear drum, leading t temprary lss f hearing. Effect f pressure n the vlume f a gas. When pressure is increased n a gas trapped in a suitable cntainer, its vlume decreases. Fr example, if ne blcks ff the utlet f a bicycle pump and then tries t push the pistn dwn the pump, the air in the barrel f the pump is cmpressed. Releasing the handle allws the gas t expand back t its riginal vlume (assuming nne leaked ut!). Further, as the pistn is pushed dwn the barrel, increasing resistance is felt, until ultimately mre frce than ne can supply is needed t cmpress the air. Careful bservatins f the relatinship between the pressure applied t a gas and its vlume have been made using gases trapped in a glass clumn. The pressure is cnveniently supplied by a mercury reservir which can be placed at measured heights. These experiments shw that prvided the temperature remains unchanged, the vlume f a trapped gas is inversely prprtinal t the applied pressure and this relatinship is knwn as BOYLE'S LAW. This means that, as pressure is increased n the gas, its vlume decreases prprtinately. Fr example, if the pressure (P) were dubled, the vlume (V) wuld be halved. Byle's law can be expressed by the equatin P V = cnstant r P 1 V 1 = P 2 V2 where V 1 and V 2 are the vlumes when the pressures are P 1 and P 2 respectively. As an example, 1.0 L f air at 1.0 atmsphere pressure at a cnstant temperature wuld ccupy 0.5 L at 2.0 atmspheres as 1.0 x 1.0 = 0.5 x 2. Diagrammatically, the relatinship between pressure and vlume culd be shwn as illustrated n the next page. ST2-1

2 Vlume (L) Pressure (atm) The accmpanying diagrams illustrate hw the vlume f a gas changes as the pressure increases. In terms f the kinetic mlecular thery presented in Supplementary Tpic 1, the reduced vlume available t the gas results in mre cllisins between the gas mlecules and the cntainer walls, leading t increased pressure, as illustrated in this diagram. Gases under pressure have the ability t d wrk when they are allwed t expand again, due t reductin f the pressure, thus releasing the stred energy in the cmpressed gas. Examples include the use f air cmpressrs t drive jack hammers, and the firing f pellets in an air rifle. Check yur understanding f this sectin. Calculate the pressure required t cmpress air which ccupies a vlume f 1.00 L at 1.00 atmspheres t 0.10 L at the same temperature. Effect f temperature n the vlume f a gas. When a gas in a fixed vlume cntainer is heated, the pressure inside the cntainer increases as the gas cannt expand. If the cntainer is ne which maintains cnstant pressure instead f cnstant vlume, (e.g. a pistn in a cylinder), the vlume (V) expands as temperature (T) increases. A graph f the vlume pltted ver a range f temperatures is fund t be a straight line, as illustrated n the next page. If this line were t be extraplated t zer vlume, the temperature wuld be 273 C. As n sample f matter culd reduce t zer vlume, this temperature represents the lwest theretical temperature pssible. ST2-2

3 ST2-3 A temperature scale called the KELVIN SCALE adpts this temperature as its zer, smetimes called "ABSOLUTE ZERO", and uses the same interval fr a degree as is used fr the Celsius r centigrade scale. Thus zer n the Celsius scale wuld be 273 n the Kelvin scale, shwn as 273 K (n degrees sign is used). Likewise, the typical rm temperature in summer f 25 C is 298 K. If the Kelvin scale were used, the vlume f a gas held at cnstant pressure is DIRECTLY PROPORTIONAL t the temperature. i.e. V = Cnstant T, r V 1/T 1 = V 2/T 2 fr tw temperatures T 1 and T 2. This relatinship is referred t as CHARLES'S LAW. The fllwing diagrams illustrate hw the vlume and pressure f a cntained gas respnd t temperature changes.

4 ST2-4 As an example, 1.0 L f air at 25 C (298 K) expands when heated t 100 C (373 K) s that the final vlume is 1.0 x 373/298 L = 1.25 L at the same pressure. Check yur understanding f this sectin. Calculate what temperature 1.0 L f air at 273 K wuld have t be heated t in rder that its vlume increased t 2.0 L at the same pressure. The vlume, pressure and temperature relatinships fr gases given by the laws f Byle and Charles can be cmbined int a single equatin. Fr tw sets f cnditins 1 and 2, P 1 V 1 = P 2 V 2 T 1 T2 where T is in Kelvin. Units used fr pressure. There are numerus units used t measure the pressure f gases. The mst cmmnly used are atmspheres, millimetres f mercury and Pascals. As atmspheric pressure varies cnstantly with weather cnditins and als with altitude, it is necessary t define ne atmsphere f pressure as 760 millimetres f mercury (mmhg). This refers t the height f a clumn f mercury that can be supprted in a glass tube in an instrument called a barmeter. The Pascal (Pa) is the SI unit f pressure and ne atmsphere crrespnds t kilpascals (kpa). Example1. A mtr car tyre at 25.0 C (298K) has a vlume f 50.0 litres at a pressure = 240 kilpascals. After travelling n a ht rad, the tyre vlume is 50.5 litres and the temperature f the air inside is 70.0 C (343K). Calculate the pressure nw in the tyre. P 1 = 240 kpa, V 1 = 50.0 L, T 1 = 298 K P 2 =?, V 2 = 50.5 L, T 2 = 343 K Substituting in the cmbined Byle s and Charles s law equatin, P 1 V 1 = P 2 V 2 T 1 T = P P 2 = 274 kpa Kinetic mlecular explanatin f Charles s law. The kinetic mlecular mdel f gases explains Charles's Law in terms f the mlecules mving faster at higher temperatures and thus having mre energy. Cnsequently cllisins between the mlecules and the walls f the cntainer ccur

5 ST2-5 mre frequently and result in mre frce n the walls - i.e. an increase in pressure ccurs. If the cntainer walls are nt rigid, then accrding t Byle's Law, the vlume will expand. The effect f temperature n gas pressure and vlume is seen in the increase in pressure bserved when the tyres f a mtr car becme htter as the car is driven. The tyres are able t increase their vlume nly slightly, leading t increased pressure at the higher temperature as in the abve example. Hence ne needs t check the pressures when the tyres are cld t avid under-inflatin. The kinetic mlecular thery s explanatin f Charles s Law shwing the relatin between vlume and temperature at cnstant pressure is illustrated in the fllwing diagrams. Mixtures f gases. If a mixture f gases is in an enclsed cntainer, then each gas expands t unifrmly and independently fill the cntainer and the PARTIAL PRESSURE f each gas is the pressure which it wuld exert if that gas alne ccupied the cntainer. The ttal pressure is the sum f all the partial pressures f all the cmpnent gases in the mixture. Fr a mixture f gases 1, 2,3... P - P + P + P +... ttal Slubility f gases in liquids. In earlier Tpics, it was shwn hw inic slids such as sdium chlride disslve in water because the ins cmbine with the plar water mlecules, releasing enugh energy t break the inic crystal lattice. Gases als disslve in liquids such as water, but usually they d nt prduce ins in slutin. Fr mst gases, instead f the relatively strng attractive frces existing between ins and water mlecules, there are much weaker attractins which allw at least sme f the gas t transfer int the disslved state. Fr example, the disslutin f xygen gas in water culd be represented by the equatin O 2(g) O 2(aq) where O 2(aq) represents the assciatin between water mlecules and the xygen mlecule. The amunt f gas present in a given slutin depends n the fllwing three factrs.

6 ST2-6 (i) the particular gas (ii) the temperature (iii) the pressure f gas ver the slutin. (i) Sme gases interact t a significantly greater extent with the slvent than d ther gases. Fr example, the gas ammnia, NH 3, is very sluble in water because it can + hydrgen bnd t the water mlecules (Tpic 13) and als it frms ins f NH 4 and OH t a small extent. By cmparisn, gases such as xygen and nitrgen are much less sluble in water because they have n hydrgen bnding with the slvent and d nt frm ins in water. Hydrgen chlride is very sluble in water due t the reactin t frm hydrchlric acid which arises frm the cmplete inizatin f hydrgen + chlride t H and Cl ins as shwn in the fllwing equatin. + HCl(g) H (aq) + Cl (aq) Hwever, generally gases d nt frm ins r hydrgen bnd with the slvent. (ii) The slubility f a gas in any slvent decreases as the temperature increases. If water is biled fr lng enugh, all disslved gases will be expelled. Hwever, if the biled water is then left expsed t the air fr a while, gases frm the atmsphere will again disslve until their cncentratins return t the values that existed befre the water was biled. Once this ccurs, a dynamic equilibrium is established between gas disslving and gas escaping frm the slutin. The reductin in gas slubility with increased temperature is due t the increased energy f the disslved gas mlecules which allws them t escape frm the slvent. e.g. O (aq) + heat O (g) 2 2 The reductin in slubility f a gas with increased temperature is the ppsite effect t that bserved fr mst slids disslving. The reasn is that increasing the temperature imparts increased energy t the disslved gas mlecules which can then escape frm the disslved state t the gaseus state mre easily, while fr slids, the additinal energy imparted at a higher temperature allws its cmpnent ins r mlecules t escape frm the crystal lattice mre easily and thus g int the disslved state. The reduced slubility f gases in slvents at higher temperatures has a drastic effect n aquatic life. Reduced xygen cntent in water due t heating (e.g. by discharge f ht water frm pwer statin cling twers) can cause the death f fish and ther xygen-breathing aquatic animals. Cnversely, cler cean temperatures encurage marine life, fr example the Humbldt current that flws nrth alng the cast f Suth America. The fllwing table gives the slubilities f a number f gases at 1 atmsphere pressure and a temperature f 0 C in mle per litre. The last tw gases in the list have much strnger interactins with water due t inisatin and/r hydrgen bnding. Gas Slubility (ml/l) nitrgen xygen hydrgen carbn mnxide hydrgen sulfide ammnia 11 hydrgen chlride 12

7 ST2-7 (iii) Increased pressure f a gas abve a slvent causes mre gas t disslve. This effect is illustrated in the fllwing diagram. Henry's Law states that the slubility f a gas in a slvent is directly prprtinal t the pressure f the gas abve the slutin. Just as slutins f slids in liquids reach saturatin when sufficient slid has been added, s t d slutins f gases becme saturated when n mre f the gas can be made t disslve, n matter hw high the pressure used. The amunt f gas that can disslve befre saturatin is reached at a given temperature will therefre increase as the pressure f the gas ver the slutin is increased. If a mixture f gases is present ver the liquid, then the amunt f each disslving is prprtinal its partial pressure ver the slutin. Examples f Henry's Law in actin include the "divers bends" and the prductin f sda water in a sda siphn. Divers bends result frm nitrgen which has disslved t a greater extent in the bld at the higher pressures supplied in rder t balance the pressure f water at great depths. While the diver stays deep dwn in the water, the nitrgen remains disslved, but if the diver surfaces rapidly the nitrgen slubility falls t match the external pressure. The excess nitrgen cmes ut f slutin in the bld as bubbles which cause cnsiderable pain and pssibly death due t blckage f bld vessels. The slubility f xygen in the bld wuld als be reduced as the diver surfaced, but it can be remved in the bdy by respiratin. Carbnated drinks are made by frcing carbn dixide t disslve at high pressure in water. While the drink remains sealed, the gas stays in slutin but when the pressure is released by remving the lid, the carbn dixide cmes ut f slutin rapidly and frms the familiar bubbles assciated with fizzy drinks. The prcess f disslutin f a gas in water is hastened by increasing the surface area f water in cntact with the gas. This is the reasn fr bubbling air thrugh the water in an aquarium tank in rder t increase the amunt f xygen available. The ideal gas equatin. The cmbined laws f Byle and Charles given previusly shw that PV/T fr any fixed amunt f gas is a cnstant prvided that T is expressed in the Kelvin temperature scale. If an amunt f gas equal t exactly 1 mle is used, this cnstant is called the UNIVERSAL GAS CONSTANT, symblised as R. The numerical value f R will depend n the units used t express the pressure and vlume f the gas. If the pressure is measured in atmspheres and the vlume measured in litres

8 ST2-8 (remembering that T must always be in Kelvin), then regardless f which gas is taken, the cnstant R has the value litre atmspheres per Kelvin mle. It can be shwn that pressure vlume has energy units and s if the SI derived units fr P (kilpascals) and vlume (litres) are used, then the resulting energy units are in the SI system, Jules. Using kilpascals and litres, the value and units fr R becme jules per Kelvin mle (written as J K ml ). Fr n mles f gas, the equatin becmes PV = nr r PV = nrt T This is called the IDEAL GAS EQUATION but it applies even t real gases subject t the limits given previusly where pressures are nt extremely high r temperatures extremely lw. One implicatin f this equatin is that the vlume f exactly ne mle f any gas at a specified temperature and pressure is always the same. Fr example, at rm temperature and pressure which are generally taken as 25 C (298 K) and ne atmsphere (101.3 kpa), the MOLAR VOLUME f any gas is 24.5 L. Example 2. In Tpic 9, Tutrial questin 1(a), the reactin shwn in the fllwing equatin was given: O 2(g) + 2SO 2(g) 2SO 3(g) (a) Starting with 1.00 mle f xygen and 2.00 mle f sulfur dixide, calculate the vlume f sulfur trixide prduced at 25 C and kpa assuming cmplete reactin. Frm the equatin, ne mle f xygen prduces tw mles f sulfur trixide. Mlar vlume f any gas at 25 C and kpa = 24.5 L. vlume f SO (g) at these cnditins = L = 49.0 L 3 (b) Calculate the vlume f this amunt f sulfur trixide at 50 C and kpa. Either use the cmbined Byle s and Charles s law equatin r use the ideal gas equatin. Either methd requires the temperature t be in the Kelvin scale. 50 C = ( ) K = 323 K Using P V = P V T 1 T = V V 2 = 26.9 L Using the ideal gas equatin, PV = nrt, V = V = 26.9 L

9 ST2-9 Objectives f this Tpic. When yu have cmpleted this Tpic, yu shuld have achieved the fllwing gals: 1. Understand that all bjects are subject t atmspheric pressure which depends n height abve sea level. 2. Knw the qualitative and quantitative relatinship between the vlume f an enclsed gas and its pressure at a fixed temperature. 3. Knw the qualitative and quantitative relatinship between the vlume f a gas and its temperature n the Kelvin scale. 4. Understand hw the Kelvin temperature scale is derived and be able t cnvert Celsius and Kelvin temperatures. 5. Be able t apply the quantitative relatinships frm Byle's law and Charles's law t sme simple calculatins. 6. Knw that the amunt f gas that disslves in a liquid is determined by the temperature f the liquid, the pressure f gas ver the liquid and characteristics f each individual gas. 7. Knw that in a mixture f gases in an enclsed cntainer, each gas expands t unifrmly fill the cntainer and exerts its partial pressure which is the pressure it wuld exert if that gas slely ccupied the cntainer. 8. Knw that the ttal pressure in a mixture f gases is the sum f the partial pressures f all the cmpnent gases. 9. Knw that gases disslve in liquids as a result f interactins between the gas mlecules and the slvent mlecules. 10. Be able t differentiate between the effects f increased temperature n the slubility f slids in liquids and gases in liquids. 11. Be able t explain the gas laws in terms f the kinetic mlecular mdel. 12. Be able t use the ideal gas equatin in cmputatins invlving vlumes, pressures, temperatures and amunts f gases.

10 ST2-10 SUMMARY. Gases cnsist f particles (atms r mlecules) which are in rapid mtin, clliding with each ther and with the bundaries f their cntainers. One cnsequence f these cllisins is the existence f air pressure. At sea level, the pressure due t the atmsphere is largely unnticed but very significant. The vlume, temperature and pressure f a cntained gas are related by tw laws: Byle's law which states that the vlume f gas is inversely prprtinal t the applied pressure at a fixed temperature and Charles's law which states the vlume is directly prprtinal t the abslute temperature at a fixed pressure. These laws can be embdied in a single relatinship, viz P V/T (T in Kelvin) fr any enclsed gas is a cnstant. The relatin f vlume t temperature f a gas leads t the prpsal f the abslute r Kelvin temperature scale which is based n a zer which wuld crrespnd t the temperature at which the gas wuld theretically have zer vlume. This temperature is 273 C, and a ne degree interval is the same as n the Celsius scale. The ideal gas equatin relates the laws f Byle and Charles t the amunt f gas present under the prevailing cnditins by including the cnstant R. That equatin is PV = nrt and if pressure is specified as kilpascals, vlume as litres and temperature as Kelvin, then R has the value jules per Kelvin mle. The ideal gas equatin is subject t the same limitatins as the laws f Byle and Charles but is a satisfactry representatin f real gas behaviur prvided the temperature is nt very lw r the pressure extremely high. In a mixture f cntained gases, each gas expands unifrmly and independently t ccupy the ttal vlume f the cntainer and each gas exerts its wn partial pressure. The sum f the partial pressures f all the gases in the mixture is equal t the ttal gas pressure. The slubility f gases in liquids such as water decreases at higher temperatures (due t the mlecules having mre energy t escape frm the slutin), increases with increased pressure f the gas ver the slutin, and als depends n factrs such as the structure f the gas mlecules and hw they interact with the slvent. TUTORIAL QUESTIONS - SUPPLEMENTARY TOPIC Why is it necessary t pressurise the cabins f high flying aircraft? 2. What des the barmeter measure, and why des its reading vary frm day t day? 3. Hw is the Kelvin temperature scale defined? What wuld 20 C be n the Kelvin scale? 4. Air (1.0 L) at 1.0 atmsphere pressure and 25 C has the applied pressure increased t 10 atmspheres at the same temperature. What wuld be the new vlume bserved? 5. What wuld be the vlume f the same sample f gas in the previus questin if the temperature were t be increased t 300 C, the pressure remaining at 1.0 atmsphere?

11 ST Why may the discharge f water used fr cling frm industrial plants pse prblems fr waterways? 7. A glass f water taken frm the tap in winter ften frms many small bubbles thrughut the liquid upn standing in a warm rm. Explain this bservatin. 8. Explain hw the expansin f gases with increased temperature is relevant t the peratin f the internal cmbustin engine. 9. In terms f the kinetic mlecular thery, explain Byle's Law and Charles's Law. 10. What causes the "bends" suffered by divers wh surface quickly frm significant depths f the cean? Hw des treatment in cmpressin chambers cure them? 11. Why is the gas hydrgen chlride much mre sluble in water than chlrine r hydrgen gases? 12. The slubility f an inic cmpund such as cpper(ii) sulfate increases if the temperature f the slutin is raised but the slubility f a gas such as carbn dixide is reduced at higher temperatures. Explain why this is s. 13. State Henry's law. Give tw examples f Henry's law in actin. 14. What will be the vlume f a sample f carbn dixide at 98.0 kpa if its vlume at 96.4 kpa is 223 ml, the temperature being unchanged? 15. What vlume will be ccupied by a sample f hydrgen at 153 kpa if the vlume at 98.6 kpa is 325 ml, the temperature being held cnstant? 16. A sample f hydrgen sulfide was cllected in a 250 ml flask at a pressure f 98.6 kpa and 310 K. What vlume wuld the gas ccupy at 369 kpa and 313 K? 17, A mixture f Ar (3.28 x 10-3 mle) and N2 (1.92 x 10-2 mle) was cllected in a vessel whse capacity was 62.5 ml. What wuld be the ttal gas pressure at 298 K? ANSWERS TO TUTORIAL SUPPLEMENTARY TOPIC 2 1. The atmspheric pressure utside f high flying aircraft is cnsiderably less than the ne atmsphere that we nrmally experience, s unless the interir pressure is maintained at clse t ne atmsphere, there wuld be insufficient xygen t supprt life. Sudden depressurisatin in aircraft is nt unknwn and in this situatin, xygen masks drp frm the ceiling. 2. A barmeter measures atmspheric pressure. Air pressure varies due t areas f high and lw pressure regins in the atmsphere that cnstantly circle the earth as seen n the weather maps. This cnstant variatin results frm heating effects frm the sun and ceans and the mtin f the earth.

12 ST The Kelvin temperature scale is defined by zer Kelvin being the temperature at which, accrding t Charles s Law, the vlume f an ideal gas wuld be zer and this crrespnds t 273 degrees Celsius. [This is unattainable as the gas culd nt disappear.] A ne degree interval n the Kelvin scale is defined as being the same as fr the Celsius scale. T cnvert a temperature expressed n the Celsius scale t Kelvin, add 273. Thus 20 C wuld be ( ) K = 293 K. Nte that n degree sign is used when temperatures are expressed as Kelvin. 4. Frm Byle s law, P 1 V 1 = P 2 V 2, (nting that T is cnstant), substitute the tw sets f cnditins 1 and = 10 V 2 V 2 = 0.10 L 5. Frm Charles s law, V 1 / T 1 = V 2 / T 2, (nting that P is cnstant), substitute the tw sets f cnditins 1 and 2 where T is in Kelvin. 1.0 / 298 = V 2 / ( ) = V 2 / 598 V 2 = 2.01 L 6. The slubility f gases decreases as the water temperature increases, s less xygen wuld be available fr marine rganisms. In extreme cases, aquatic life dies due t there being insufficient disslved xygen as a result f the high water temperature. 7. Water frm the tap cntains gases disslved frm the atmsphere, mstly xygen and nitrgen. As the water temperature rises t rm temperature, sme f the gases may exceed their maximum slubility fr the cnditins f their partial pressure and temperature, causing them t cme ut f slutin rapidly as bubbles. 8. A mixture f air and petrl vapur is ignited in the cylinder f the internal cmbustin engine when the pistn is at the tp f the cylinder. The heat released by the cmbustin causes the mixture f gases in the cylinder t expand and increase the pressure in the cylinder. This leads t the pistn being frced dwn the cylinder. The mtin f the pistns is transferred t a crankshaft which ultimately leads t the mtin f the car s wheels. 9. Accrding t the kinetic mlecular thery, gases cntain rapidly mving particles (mlecules r atms) which are clliding with each ther and the walls f any cntainer in which the gas is trapped. The pressure bserved fr a trapped gas is the result f the particles clliding with the walls f the cntainer. The mre cllisins that are ccurring, the greater will be the bserved pressure, s if the vlume is reduced as in a pistn/cylinder system, then there will be mre cllisins between the particles and the walls f the cntainer and thus an increase in pressure. If the temperature is kept cnstant s that the particles d nt change their energy, this leads t Byle s law, P V = a cnstant. The thery als pstulates that the energy f the particles is related t the

13 ST2-13 temperature, s increasing the temperature causes there t be mre cllisins with higher energy. This translates t an increase in vlume if the gas is in a cnstant pressure envirnment r t an increase in pressure if the gas is trapped in a cnstant vlume system. If the temperature is measured in Kelvin, the relatin V / T = a cnstant results which is Charles s law. 10. Divers are subjected t the external pressure f the water at the diving depth and in rder t breathe, air must be supplied at a pressure t balance the water pressure. Frm Henry s law, the higher air pressure leads t mre xygen and nitrgen mlecules disslving in the bldstream. If the diver surfaces quickly, the disslved gases, mainly the nitrgen, cme ut f slutin and frm bubbles which can damage nerves and bld vessels. The result is extreme pain and even death. T avid the bends, divers surface at a cntrlled rate with stps fr perids at gradually decreasing depths in rder t give enugh time fr the gases t be expelled via the lungs. 11. Hydrgen chlride gas cnsists f cvalent mlecules but it reacts vigrusly + with water t frm H (aq) and Cl (aq) ins, a slutin called hydrchlric acid which is a strng acid because it is ttally inised. This prcess allws much mre HCl gas t disslve cmpared t the amunt that wuld disslve withut the reactin taking place. Hydrgen and chlrine gases d nt react with water t frm ins in slutin and s withut this mechanism, their slubilities in water are cnsiderable less than that f hydrgen chlride. 12. Inic slids disslving in water require energy fr the ins t break away frm the attractin f the crystal lattice, s higher temperatures allw mre ins t escape and thereby increase the slubility. Gases disslved in liquids experience an attractin t the slvent mlecules which maintains them in the disslved state. Hwever, as mre energy is supplied by heating, the disslved gas mlecules vercme the attractin t the slvent and escape mre readily frm the slutin. Biling a slutin f a gas such as carbn dixide will ultimately expel all f the CO mlecules frm the slutin Henry s law states that at a given temperature the slubility f a gas in a liquid is prprtinal t the pressure f that gas abve the liquid. Examples f this law in actin include carbnated drinks where carbn dixide is frced under pressure t disslve in water and the disslutin f xygen in water which is essential fr all aerbic aquatic life PV = cnstant r P V = P V P1 = 96.4 kpa and V1 = 223 ml P2 = 98.0 kpa and V2 =? S 96.4 x 223 = 98.0 x V2 V2 = (96.4 x 223) / 98.0 = 219 ml [Nte: the units f P and V must be the same n bth sides f the equatin.]

14 ST As temperature is cnstant, Byle's Law can be used. PV = cnstant r P1V1 = P2V2 P1 = 98.6 kpa and V1 = 325 ml P2 = 153 kpa and V2 =? S 98.6 x 325 = 153 x V2 V2 = (98.6 x 325) / 153 = 209 ml 16. The temperature and pressure bth change s the cmbined Byle's and Charles's Law expressin must be used. P1V1 / T1 = P2V2 / T2 P1 = 98.6 kpa, V1 = 250 ml and T1 = 310 K (Nte that temperature must be expressed in Kelvin) P2 = 369 kpa, V2 =? and T2 = 313 K S (98.6 x 250) / 310 = (369 x V2) / 313 V2 = (98.6 x 250 x 313) / (310 x 369) = 67.4 ml 17. The Ideal Gas Equatin is required t slve this prblem. PV = nrt The cnstant R has a value which depends n the units fr P and V. (Units fr n are always mles). If P is expressed in kpa and V in litres, R = J K-1 ml-1. Temperature is in Kelvin. P =? kpa, V 62.5 ml = L and n = ttal mles f gas present = 3.28 x x 10-2 = x 10-2 ml R = J K-1 ml-1 and T = 298 K (Nte: T must be in Kelvin) P x = x 10-2 x x 298 P = (2.248 x 10-2 x x 298) / = 891 kpa