The following information relates to Questions 1 to 4:

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1 Th following information rlats to Qustions 1 to 4: QUESTIN 1 Th lctrolyt usd in this ful cll is D watr carbonat ions hydrogn ions hydroxid ions QUESTIN 2 Th product formd in th ful cll is D hydrogn gas oxygn gas watr carbon dioxid Th School For Excllnc 2018 Unit 3 & 4 hmistry Topic Tst Pag 1

2 QUESTIN 3 Which of th following statmnts is corrct? D lctrod is th cathod lctrod is th anod th lctrolyt flows from th cathod to th anod th lctrons flow from th cathod to th anod QUESTIN 4 Th half quation occurring at th cathod would b ( aq) 2H 4 4H( aq) 4H 4 2H D 2H 2H QUESTIN 5 Ful clls ar lctrochmical clls that convrt chmical nrgy into lctrical nrgy. Th hydrogn-oxygn ful cll is an xampl of a common ful cll. Th raction that taks plac at th cathod in an acid hydrogn-oxygn ful cll is H H 2 ( g ) 2 H 2H 2 2 ( g ) 2 H 2 g ) 4H 4 2H D g ) 2H 4 4H Th School For Excllnc 2018 Unit 3 & 4 hmistry Topic Tst Pag 2

3 QUESTIN 6 For th ful cll shown, Writ an ovrall quation. Writ half quations for th cll s opration. (c) ompar th fficincy of this ful cll with th fficincy of a thrmal powr station. (d) Stat on main advantag and on main disadvantag. Th School For Excllnc 2018 Unit 3 & 4 hmistry Topic Tst Pag 3

4 QUESTIN 7 Som popl hav suggstd that if mor ful clls, such as th hydrogn-oxygn wr to b usd to produc lctricity, thr would b an improvmnt to th air pollution and grn hous problms. Explain th rasoning bhind this. QUESTIN 8 Th principl storag form of nrgy in plants is starch; which is a larg branchd polymr of glucos. Larg quantitis of glucos ar also found in cllulos; th structural support matrial in plants. n way in which it may b possibl to utilis th nrgy stord in plants is by convrting cllulos and starch to glucos and thn using th glucos producd as a ful in a ful cll. Writ th ovrall raction that occurs in this cll. Using th ovrall quation and th oxidation half quation blow, dtrmin th rduction half quation for th ful cll H 6H 6 24H 24 E⁰= -0.01V ( Th School For Excllnc 2018 Unit 3 & 4 hmistry Topic Tst Pag 4

5 (c) alculat th EMF of this ful cll undr standard conditions. (d) If th fficincy of this cll is 95%, calculat th amount of nrgy that could b thortically drivd from th raction of 1 mol of glucos in such a ful cll. Stat your answr to th narst whol numbr. () Stat a rason why th fficincy of fuls clls so high. (f) Hydrogn is th ful that is most commonly usd in ful clls. Giv on advantag and on disadvantag of using hydrogn gas in th ful cll, in comparison to th burning of fossil fuls such as coal. Th School For Excllnc 2018 Unit 3 & 4 hmistry Topic Tst Pag 5

6 QUESTIN 9 Ethanol nrgy from thanol can also b convrtd into lctricity using Solid xid Ful lls as shown blow. Th ovrall cll quation and th raction occurring at th anod ar shown blow. nod: vrall: Writ an quation for th raction occurring at th cathod. List thr functions of th lctrods in a ful cll. Th School For Excllnc 2018 Unit 3 & 4 hmistry Topic Tst Pag 6

7 QUESTIN 1 QUESTIN 2 QUESTIN 3 QUESTIN 4 QUESTIN 5 lkalin Ful ll Ractions: nod: H athod: 2 ( g ) 2 H 2H 2 g ) 2H 4 4H 2H 2H l vrall: ) cid Ful ll Ractions: nod: H 2 ( g ) 2 H 2 athod: g ) 4H 4 2H vrall: 2H 2H QUESTIN 6 Th ovrall quation is th production of watr from oxygn and hydrogn: 2H 2H This is quit a tricky qustion. To answr it, rmmbr that th lctrolyt will appar in both half quations. Us th diagram to hlp you. t th cathod, oxygn racting with carbon dioxid to form carbonat ions. t th anod, hydrogn is combining with carbonat ions to form carbon dioxid and watr. This will allow you to form sklton quations which you can thn balanc to obtain th ovrall quation. Sklton quations: 2 H g ) 3 2 3( aq) H athod: ( aq) nod: H ( 3 2H 2 4 Ths two quations would cancl to giv th ovrall quation. Th School For Excllnc 2018 Unit 3 & 4 hmistry Topic Tst Pag 7

8 (c) (d) Th ful cll has an fficincy of around 60% compard to 30% for a powr station. n advantag is that opration is not intrruptd but a disadvantag is th pric tag. QUESTIN 7 Th only products of th hydrogn-oxygn ful clls ar watr and hat. No grn hous gass or othr pollutants ar rlasd in th atmosphr. QUESTIN 8 Th ovrall quation will b th sam as th combustion raction of glucos. H 6 6 6H ( Th half quation givn shows th convrsion of glucos into carbon dioxid. Th othr half quation will show th convrsion of oxygn into watr. H 4H 4H 2 2 ( 2H ( 2H 4 2 ( 2H 2 ( o 4H 4 2H E 1.23V (c) g ) 2 ( o 6 24H 24 H 6H E 0.01V g ) ( Not: Th scond quation has bn rvrsd to turn it into a rduction raction as it would appar on th lctrochmical sris. Sinc th E⁰ valu was quotd for th oxidation raction and w hav now turnd it into a rduction raction, th sign of its valu will chang. EMF V (d) Rfrring to th data sht th molar nthalpy of combustion of glucos is 2816 kjmol 1. t 95% fficincy th amount of nrgy (answr must b positiv) that could b rlasd is kjmol 1 () Th chmical nrgy stord in th bonds of th ful is dirctly convrtd into lctrical nrgy with littl nrgy bing lost as hat. Th School For Excllnc 2018 Unit 3 & 4 hmistry Topic Tst Pag 8

9 (f) dvantags: n of: End products/by products ar nvironmntally frindly. End products of combustion of coal ar significant contributors to th grnhous ffct and global warming. Hydrogn is a rnwabl nrgy sourc coal is not. Thr ar abundant supplis of hydrogn whras th rsrvs of coal ar rapidly dplting. Disadvantags: n of: Hydrogn is xpnsiv to obtain from watr coal is mor cost ffctiv. Th unit rquird to combust hydrogn is xpnsiv to run and not portabl. QUESTIN 9 vrall: nod: in th ovrall quation com from th raction occurring at th anod. This lavs oxygn to b rducd at th cathod. xid ions will appar as a product at th cathod in ordr to cancl out thos apparing as products at th anod. athod raction: bcoms Elctrods must b abl to conduct lctricity, sparat th ractants, allow contact btwn ractants and th lctrolyt and act as catalysts. Th School For Excllnc 2018 Unit 3 & 4 hmistry Topic Tst Pag 9

Electrochemistry L E O

Electrochemistry L E O Rmmbr from CHM151 A rdox raction in on in which lctrons ar transfrrd lctrochmistry L O Rduction os lctrons xidation G R ain lctrons duction W can dtrmin which lmnt is oxidizd or rducd by assigning oxidation