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Probably very easy question on half equations

Use the following half equations to form overall equations by multiplying out and then adding
The half equations need to be balanced first

O2 + H+ + e- ------> H2O
SbH3 --------> Sb + H+ + e-

Thanks
Reply 1
Avatar for anish1411
anish1411
Hummm not really sure but I think it's like this...

First you have to balance the top equation:

O2 + 4H+ + 4e- ----> 2H2O

Then the bottom one:

SbH3 ----> Sb + 3H+ + 3e-

Then balance by the number of electrons (multiply them both by any number that will make the number of e- the same in both):

3O2 + 12H+ + 12e- ----> 6H2O
4SbH3 ----> 4Sb + 12H+ + 12e-

The combine the two equations:

4SbH3 + 3O2 + 12H+ ----> + 4Sb + 6H2O + 12H+

The H+'s cancel to give the final equation:

4SbH3 + 3O2 ----> 4Sb + 6H2O

The main thing I'm not sure about is whether you can just do what I did in the first two steps, because it seems strange they would give you the equations like you wrote in your post, if you're just supposed to just change it all anyway... :-\
Reply 2
Avatar for shyopstv
shyopstv
OP
15
Yeah that seems to be right (just looked at chemguide.co.uk just to make sure) thanks!
Reply 3
Avatar for jakatak
jakatak
1
I dont think that's right. You're not trying to cancel out the H's but the electrons. As there is one electron involved in each half equation u don't need to do any multipyling. Just cancel out the electrons:

O2 + H+ + SbH3------> H2O + Sb + H+
Reply 4
Avatar for kpg
kpg
11
jakatak
I dont think that's right. You're not trying to cancel out the H's but the electrons. As there is one electron involved in each half equation u don't need to do any multipyling. Just cancel out the electrons:

O2 + H+ + SbH3------> H2O + Sb + H+


The half equations need to be balanced and if you end up with hydrogen ions on both sides of the equation you can cancel them down.
Reply 5
Avatar for anish1411
anish1411
jakatak
O2 + H+ + SbH3------> H2O + Sb + H+


Yah that's what I thought first! But that isn't balanced, so you gotta do all that other malarkey.
Reply 6
Avatar for anish1411
anish1411
What the hell is Sb anway lol? I've never heard of it, you must do a funny board!
Reply 7
Avatar for jakatak
jakatak
1
oh yeah I didn't even think about cancelling out the H+'s or balancing it. Never had to worry about that with any half equations before though.
Reply 8
Avatar for Cirsium
Cirsium
19
Sb is antimony
jakatak
I dont think that's right. You're not trying to cancel out the H's but the electrons. As there is one electron involved in each half equation u don't need to do any multipyling. Just cancel out the electrons:

O2 + H+ + SbH3------> H2O + Sb + H+
I'm afraid that's wrong because the equation isn't balanced. You CAN balance that equation to get the marks, but it's a very difficult one to balance like that. The method they want you to use follows thusly:

Balance the half equations first

O2 + 4H+ + 4e- ------> 2H2O
SbH3 --------> Sb + 3H+ + 3e-

Multiply each equation by something to get the electrons to balance (multiply the top one by 3 and bottom by 4)

3O2 + 12H+ + 12e- ------> 6H2O
4SbH3 --------> 4Sb + 12H+ + 12e-

combine the equations and cancel the electrons

3O2 + 12H+ + 4SbH3 ------>4Sb + 12H+ + 6H20

Check: charge is balanced and same number of moles of each element on each side so looks right. You could cancel the H+'s I suppose, but I wouldn't do that unless it asked for an ionic equation.

Edit: Rats - just noticed that anish1441 was right. What a waste of effort :mad:. Well done anish1441 :rolleyes:

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