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How do I combine half equation in this question? :S

Some fuel cells are used to produce energy from the combination of hydrogen and
oxygen. The half-equations for a hydrogen-oxygen fuel cell in alkaline solution are:

2H2O(l) + 2e– ---> H2(g) + 2OH–(aq) E cell : –0.83 V

½O2(g) + H2O(l) + 2e– ----> 2OH–(aq) E cell : + 0.4 V

a) The equation for the cell reaction is

A.) 3H2O(l) + ½O2 ----> H2(g) + 4OH–(aq)

B.) H2(g) + 4OH– ----> 2O(l) + ½O2(g)

C.) H2(g) + ½O2 -----> H2O(l)

D.) H2 ---> H2(g) + ½O2(g)

And answer is C anyone can explain to me how and what is going on? :s-smilie:

Oh and also in the next question itself they ask about the E cell Value the thing is I know the formula which is E cell: (Right Hand electrode) - (Left hand Electrode)

But In equations I can't seem to recognize which is right and which one is left :frown:

I already kinda bit wobbly on this chapter :'(

(edited 9 years ago)

Reply 1

charco

Study Forum Helper

Original post by KL-RC

Some fuel cells are used to produce energy from the combination of hydrogen and
oxygen. The half-equations for a hydrogen-oxygen fuel cell in alkaline solution are:

2H2O(l) + 2e– ---> H2(g) + 2OH–(aq) E cell : –0.83 V

½O2(g) + H2O(l) + 2e– ----> 2OH–(aq) E cell : + 0.4 V

a) The equation for the cell reaction is

A.) 3H2O(l) + ½O2 ----> H2(g) + 4OH–(aq)

B.) H2(g) + 4OH– ----> 2O(l) + ½O2(g)

C.) H2(g) + ½O2 -----> 2O(l)

D.) H2 ---> H2(g) + ½O2(g)

And answer is C anyone can explain to me how and what is going on? :s-smilie:

I already kinda bit wobbly on this chapter :'(

The question is incorrect ...

Reply 2

KL-RC

Original post by charco

The question is incorrect ...

But this is an actual A level Question, you may go to this link if you don't believe me

http://www.edexcel.com/migrationdocuments/QP%20GCE%20Curriculum%202000/June%202012%20-%20QP/6CH05_01_que_20120619.pdf

Go down to question 5

Reply 3

charco

Study Forum Helper

Original post by KL-RC

Yes, but you have copied answer c) incorrectly !!!!

Reply 4

KL-RC

Original post by charco

Yes, but you have copied answer c) incorrectly !!!!

Ah yes you're right! Sorry my bad. :colondollar:

but uh anyway ca you help me in any way as to why is the answer C?

Reply 5

username1445490

2H2O(l) + 2e– ---> H2(g) + 2OH–(aq) E cell : –0.83 V
½O2(g) + H2O(l) + 2e– ----> 2OH–(aq) E cell : + 0.4 V

Firstly flip the more negative one as it will be an oxidation process.

2OH- + H2 --> 2H2O + 2e
1/2O2 + H2O +2e --> 2OH-

Now cancel out the electrons and cancel down anything which appears on both sides leaving

1/2O2 + H2 --> H2O