Chemistry - an illustrated guide to science (794128), страница 13
Текст из файла (страница 13)
However, repulsionbetween the non-bonding pair ofelectrons and the bonding pairs ofelectrons forces thenitrogen–hydrogen bonds slightlycloser to each other, resulting in abon d an gle of 107°. By comparison,the bond angle in methane is 109.5°.3 Physical properties ofammoniaHH3 Physical properties of ammoniaPhysical propertyAmmoniaAmmonia–77.7Carbon monoxide–33.5Methane0.59Nitrogen oxidescolorlessOzonecharacteristic unpleasant odourSulphur dioxide68 0 0 0 cm 3 in 10 0 g of wateris less dense than air and iscollected by upward delivery(downward displacement of air).● Ammonia is exceptionally soluble andcannot be collected over water.680 cm 3 of ammonia will dissolve in1 g of water at 20°C.● Ammonia dissolves in water to form asolution that is a weak alkali:NH3(g) + H2O(l)NH4 + (aq ) + OH- (aq)● Ammoniasolution is sometimesreferred to as am m on iu m hydroxide.© Diagram Visual Information Ltd.● Ammonia74PATTERNS—NON-METALSKey wordsammoniaequilibriumLe Chatelier’sprincipleproductreactantIndustrial preparation ofammonia (the Haberprocess): theory1 Reversible reaction1 Reversible reaction● Am m on iais made industrially by thereaction of nitrogen and hydrogen.● The reaction is reversible.Forward reaction:N2(g) + 3H2(g)4 moles10 0Backward reaction:10 0 °C20 0 °C902NH3(g)● The30 0 °C80Equilibrium % of ammoniaconcentration of ammonia in theequilibrium mixture depends on thepressure and temperature at which thereaction is carried out.● According to Le Chatelier’s prin ciple,if any change is made to the externalconditions (such as temperature,concentration and pressure) of asystem at equ ilibriu m , the equilibriumposition will alter so as to oppose thechange.2 moles2 Variation of percent ammonia with pressureN2(g) + 3H2(g) ➞ 2NH3(g)N2(g) + 3H2(g)∆H = –92 kJ mol –12NH3(g)reaction is exothermic; heat isgiven out.● According to Le Chatelier’s principle, adecrease in temperature will favor theforward reaction.
The equilibriumposition will move to the right in orderto oppose the decrease intemperature, so the equilibriummixture will contain more ammonia.50 0 °C403002510 020 030 040 0Pressure (atm)3 Variation of percent ammonia with temperature10 0Working rangeof catalyst9080Equilibrium % of ammonia© Diagram Visual Information Ltd.● The5010● In3 Variation of percentammonia with temperature40 0 °C60202 Variation of percentammonia with pressurethe forward reaction, four moles ofreactan ts are converted into twomoles of produ ct so there is a drop inpressure.● According to Le Chatelier’s principle,an increase in pressure will favor theforward reaction.
The equilibriumposition will move to the right in orderto oppose the increase in pressure, sothe equilibrium mixture will containmore ammonia.70Variation of % ammoniawith temperature70605040302040 0 atm20 0 atm10 0 atm50 atm25 atm100010 020 030 0Temperature (°C)40 075Industrial preparation ofammonia (the Haberprocess): schematicPATTERNS—NON-METALSKey wordsammoniacatalystequilibriumfractionaldistillationhydrocarbonhydrogennitrogenThe process● TheHydrocarbonsLiquid airraw materials for the Haberprocess are hydrogen and n itrogen .● Hydrogen is obtained by the steamreforming of hydrocarbon s, such asmethane, or the reaction of steam withcoke.CH4 (g) + H2O(g) CO(g) + 3H2(g)C(s) + H2O(g) CO(g) + H2(g)SteamreformingHydrogenNitrogenFractionaldistillationReactorTemperature:370 –450 °CPressure:80 –110 atmCatalyst:ironLiquidammoniaCoolingbelow –33.5°CUnreactedhydrogen andnitrogenis obtained from thefraction al distillation of liquid air.● The formation of am m on ia is favoredby high pressure, and the reaction isnormally carried out at 80–110 atm.
Itis also favored by low temperature, butthis also lowers the rate of reaction, soa catalyst is used. The reaction isnormally carried out at 370–450°C inthe presence of a finely divided ironcatalyst.● In reality, the reaction is not allowed toreach equ ilibriu m . A single passthrough the reactor results in about 15percent conversion to ammonia.● The reaction mixture is cooled tobelow the boiling point of ammonia, atwhich point liquid ammoniacondenses out and is removed. Themixture of unreacted hydrogen andnitrogen is recycled back into thereactor.● Around 80 percent of the ammoniaproduced each year is used to makefertilizers, including ammonia solution,ammonium nitrate, ammonium sulfate,and urea.© Diagram Visual Information Ltd.● Nitrogen76PATTERNS—NON-METALSKey wordsammoniaazeotropicmixtureexothermicnitric acidoxidationIndustrial preparationof nitric acid1 Industrial manufacture of nitric acidghj1 Preparation● Theindustrial production of n itricacid involves two stages: theoxidation of am m on ia and theabsorption of the resulting nitrogenoxides.● In the converter, a mixture ofammonia and air is passed through aplatinum–rhodium gauze and theammonia is oxidized:fk4NH3(g) + 5O2(g) 4NO(g) + 6H2O(g)!H = -909 kj mol -1● Thereaction is exotherm ic, and a largequantity of heat is produced.● Conditions are carefully controlled tominimize a competing reaction inwhich ammonia is oxidized tonitrogen:4NH3(g) + 3O2(g)cdi2N 2(g) + 6H2O(g)● Airis added to the nitrogen oxides inorder to make nitrogen dioxide and,subsequently, dinitrogen tetroxide.a2NO(g) + O2(g) 2NO2(g)2NO2(g) N 2O4 (g)tetroxide reacts with waterto produce nitric acid.e● Dinitrogenb3N2O4 (g) + 2H2O(l)4HNO3(aq) + 2NO(g)airammoniapowerplatinum rhodium catalystoxidation reactionNO, NO2, O2waterreaction with waterpumpnitric acidunreacted gas● The© Diagram Visual Information Ltd.acid from the absorption towerstypically contains 55–60 percent nitricacid by mass.
Most of the moderndemand is for acid of thisconcentration.● Nitric acid and water form anazeotropic m ixtu re (a mixture thatboils without a change incomposition) containing 68.5 percentnitric acid by mass. Thus, concentratednitric cannot be obtained bydistillation. Concentrated sulfuric acidis used to reduce the water contentand give concentrated nitric acid.abcdefghijk2 Uses of nitric acid● Overtwo thirds of nitric acidproduction is directed to makingammonium nitrate, which is used as afertilizer and in explosives.2 Summary of uses12%Nitroaromatics79%Ammonium nitrate9%Adipicacid77Nitrogen: reactions inammonia and nitric acidPATTERNS—NON-METALSKey wordsammonianitric acidoxideoxidizing agentreducing agent1 Redox chemistry (ammonia)2NH3 + 3Cl 2N2 + 6HClAmmonia reduces chlorine to hydrogen chloride and nitrogen2NH3 + 3CuO1 Redox chemistry(ammonia)3Cu + 3H2O + N 2● Am m on iais a redu cin g agen t and willreduce chlorine and heated metaloxides such as copper oxide.
Duringthe reactions, the ammonia is oxidizedto nitrogen.Ammonia reduces copper oxide to copper, water, and nitrogen2 Redox chemistry (nitric acid)C + 4HNO3CO2 + 4NO2 + 2H2O2 Redox chemistry(nitric acid)Concentrated nitric acid oxidizes carbon to carbon dioxide→● In3Cu + 8HNO3(dilute)3Cu(NO3) 2 + 4H2O + 2NO→Dilute nitric acid oxidizes copper to produce copper nitrate, water, and nitrogen oxideCu + 4HNO3(conc)Cu(NO3) 2 + 2H2O + 2NO2Concentrayed nitric acid oxidizes copper to produce copper nitrate,water, and nitrogen dioxideaddition to its properties as an acid,n itric acid is also a powerful oxidizin gagen t. It is able to oxidize both nonmetals and metals.3 Complex ammonia salts● Whenammonia solution is added dropby drop to copper(II) sulfate solution,a pale blue precipitate of copper(II)hydroxide is formed:Cu2+ (aq) + 2OH- (aq) ➞ Cu(OH) 2(s)3 Complex ammonia salts● Whenan excess of ammonia solutionis added, the pale blue precipitateredissolves, forming a deep bluesolution:ammoniasolutionCu(OH) 2(s) + 4NH3(aq) ➞[ Cu(NH3) 4 ] 2+● Thepale blueprecipitateAmmonia solutionis addedto CuSo4 solutionMore ammonia solutionis addedThe precipitate diasppears,leaving a deep royal bluesolution (a complex salt)deep blue solution contains thecomplex ion tetraamminecopper(II),[ Cu(NH3) 4 ] 2+ .● Ammonia also forms complex ionswith other metals, such asdiamminesilver(I), [ Ag(NH3) 2] + andhexaamminenickel(II), [ Ni(NH3) 6 ] 2+ .4 Tetraamminecopper(II)XXAXXSquare planarthe tetraamminecopper(II) ion, acopper ion is surrounded by fourammonia molecules in a square planararrangement.
The non-bonding pair ofelectrons on each nitrogen atom isattracted to the central positivelycharged copper ion.© Diagram Visual Information Ltd.● In4 Tetraamminecopper(II) ion78PATTERNS—NON-METALSKey wordsacidammonianitratenitric acidnitritenitrogenoxideoxidizing agentsaltBasic reactions ofnitrogen1 With metals and non-metals3Mg + N26Na + N21 With metals and nonmetalsN 2 + 3H2● Nitrogencombines directly with bothmetals, such as magnesium, and nonmetals, such as sodium and hydrogen.2 Basic reactions ofammonia● Am m on iareacts with water toproduce a soluble alkaline gas (2A).● Ammonia reacts with an acid toproduce a salt (2B).● Ammonia reacts with an oxide toproduce a metal and nitrogen (2C).● Ammonia reacts with oxygen toproduce n itric acid (2D).3 Nitric acid● Nitricacid is both a strong acid (3A)and a powerful oxidizin g agen t (3B).● Cold, dilute nitric acid producesnitrogen oxide when reacting with ametal (3C).● Hot, concentrated nitric acid producesnitrogen dioxide when reacting with ametal (3D).4 Nitratesn itrates are very soluble in water.● Group 1 metal nitrates (apart formlithium nitrate) decompose on heatingto form metal n itrites and oxygen.● Other metal nitrates decompose onheating to form metal oxides, nitrogendioxide, and oxygen.● Ammonium nitrate decomposes onheating, forming water and dinitrogenoxide.© Diagram Visual Information Ltd.● AllMg3N22Na3NFe catalyst2NH32 Basic reactions of ammoniaA NH3 + H2ONH3 + HClNH4 + + OH2NH4 ClB 2NH3 + 3CuO3Cu + 3H2O + N2C 4NH3 + 5O24NO + 6H2Othen2NO + O22NO2and4NO2 + O2 + 2H2O4HNO3D Cu(OH) 2 + 4NH3Cu(NH3) 42+ + 2OH-3 Nitric acidA HNO3 + H2OH3O+ + NO3–B C + 2HNO3CO2 + 2NO2 + H2OCu + 4HNO3Cu(NO3) 2 + 2H2O + 2NO24 NitratesA 2NaNO32NaNO2 + O2B 2Pb(NO3) 22PbO + 4NO2 + O2C NH4 NO32H2O + N2O2A soluble alkaline gas2B reducing agent2C ammonia with oxygen to make nitric acid2D complexing agent3A strong acid3B oxidizing agent4A group 1 (excluding LiNO3)4B others4C ammonium nitrate79Nitrate fertilizersPATTERNS—NON-METALSKey words1 Atmospheric nitrogenalkaliamino acidammoniachlorophyllneutralizationNitrogen → Ammonia → Nitric acidAmmonium nitrateNH3(aq) + HNO3(aq)→ NH4 NO3(aq)1 Atmospheric nitrogen● Atmosphericnitrogen is an importantraw material in the manufacture ofam m on ia and n itric acid.● Ammonia solution is alkali, whilenitric acid is acidic.● The two solutions undergo an eu tralization reaction to form thesalt ammonium nitrate.2 Ammonia nitrateFormula mass of ammonium nitrate = 14 + 4 + 14 + 3 × 16 = 80Percentage of nitrogen in ammonium nitrate =2 × 14 × 100= 35%802 Ammonia nitrate3 Nitrogen in plants● TheCHCOOHanimo acidsHCH3 CproteinsCCCCCNCCH3CHNCMgCCHCC* CH3NNCH2CCCCH2HCCCCH OCCHCHCOCHCHHCH3CH2CH3CHCH3● Plantsuse nitrogen to make am in oacids and, from these, to makeprotein s.● Plants also use nitrogen to make otherimportant chemicals, such aschlorophyll.● Ammoniumsulfate is formed by theneutralization reaction betweenammonia solution and sulfuric acid:C20 H39 CH3Chlorophyll a(In chlorophyll b, the methyl groupmarked by an asterisk is replacedby a —CHO group)4 Table of nitrogen fertilizersFormula3 Nitrogen in plants4 Nitrogen fertilizersOCompoundpercentage of nitrogen in anitrogenous fertilizer is an importantfactor in determining how muchfertilizer should be used on an area ofcrops.● Ammonium nitrate is very soluble inwater.
![](https://s.studizba.com/z.php?f=/templates/si/i/noavatar.png&w=100&h=100&t=1"){kind=avatar}
