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# Why does preferential discharge happen? Watch

1. I'm revising electrolysis (part of module C6 of the OCR Gateway GCSE course) and it mentions that if in solution, ions below hydrogen in the reactivity series will discharge at the cathode but in an electrolysis reaction with ions above hydrogen in the reactivity series, hydrogen will collect at the cathode instead. I get that the hydrogen is present if a solution is electrolysed because a solution will contain water, but I don't understand (and can't find out from Google!) why the reactivity of the ion determines whether it will collect at the cathode or not. Help? :-) Btw, it's not urgent, I don't think I have to know this for my exam, I was just interested :-)
2. (Original post by DayFlower)
I'm revising electrolysis (part of module C6 of the OCR Gateway GCSE course) and it mentions that if in solution, ions below hydrogen in the reactivity series will discharge at the cathode but in an electrolysis reaction with ions above hydrogen in the reactivity series, hydrogen will collect at the cathode instead. I get that the hydrogen is present if a solution is electrolysed because a solution will contain water, but I don't understand (and can't find out from Google!) why the reactivity of the ion determines whether it will collect at the cathode or not. Help? :-) Btw, it's not urgent, I don't think I have to know this for my exam, I was just interested :-)
you can read up on
1) standard reduction potential

2) half equations

3) combining half equations to give balanced, complete/whole equations

4) free energy and its relation to reduction potential of a cell/circuit

5) free energy and spontaneity of a reaction
3. (Original post by shengoc)
you can read up on
1) standard reduction potential

2) half equations

3) combining half equations to give balanced, complete/whole equations

4) free energy and its relation to reduction potential of a cell/circuit

5) free energy and spontaneity of a reaction
Thank you :-)

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