Urgent SL Chemistry Questions

[Drake Glau]

Yep, that'd make sense, sorry. Temperature is the average kinetic energy, so if its 298k for them all then they're all the same average kinetic energy. Only difference would be on the physics level where the velocities would change but you don't need to know that

Edited May 8, 2011 by Drake Glau

[CeciliaL]

Quick help needed pleaaase!

How to arrive at the attached redox equation from knowing that: MnO4– reacts with Fe2+ ions to form Mn2+ and Fe3+

Thanks

[Drake Glau]

It's just balancing a redox equation

MnO₄^-+Fe²⁺->Mn²⁺+Fe³⁺

MnO₄^-->Mn²⁺

Balance O with water

MnO₄^-->Mn²⁺+4H₂O

balance hydrogen with H+

8H⁺+MnO₄^-->Mn²⁺+4H₂O

Balance charge with e-

5e^-+8H⁺+MnO₄^-->Mn²⁺+4H₂O

Fe²⁺->Fe³⁺

Just balance charge

Fe²⁺->Fe³⁺+e^-

When you combine, all electrons need to cancel and since the first half reaction has 5 and your second has 1 you need to multiply your second half reaction by 5

5e^-+8H⁺+MnO₄^-->Mn²⁺+4H₂O

5Fe²⁺->5Fe³⁺+5e^-

Then start cancelling stuff (only e- in this case, other reactions will likely cancel more than just the e-)

5e^-+8H⁺+MnO₄^-->Mn²⁺+4H₂O

5Fe²⁺->5Fe³⁺+5e^-

And now just combine them making sure to put the original stuff before what you added to balance:

MnO₄^-+5Fe²⁺+8H⁺->Mn²⁺+5Fe³⁺+4H₂O