physics/chem

Physics

Use water flow through through parallel pipes as an analogy. The pressure (voltage) through two parallel piped is the same. The total amount of water through a pipe (current) is dependant to the resistance of flow (ohms) through that pipe. The combined water flow (current) in the parallel is the total current.

If you have a electric circuit, the equation to use is E=IR where E is electromotive force (voltage), I is current (amps), and R is resistance (ohms). If I have two parallel wires of different resistance (R1, R2), then the E's are the same, so I1*R1=I2*R2 & I2=R1/R2*I1. The the total flow of electrons (current) is the combined current.

Chemistry

Half cells are in essence oxidation reduction reactions---one half cell loses electrons (oxidation), the other gains electrons (reduction). The trick in such reactions is to balance the two half cells such that there are no hanging chad (electrons). That is all electrons freed in the half cell oxidation are consumed in the half cell reduction. The other thing to consider is the EMF (voltage again) listed for the half cell. If the EMF is positive it is a battery (exothermic), if not , to get the cell (reaction) to work the reaction is endothermic and you have to put work into the reaction to get it to work. The latter is, in effect, recharging a battery.

Rap

yes but how come in a series circuit the "pressure" changes/splits?

chemistry-ok maybe i should put the question in a different way, How do you balance redox reactions? it is hard to balance them the normal way in your head, so you need a different method such as the half equation method to make it easier. how do you do the half reaction method and is there any other way of balancing redox reactions?

Because in a series circuit the resistance is additive. In a series circuit the flow (current) is the same. So if you use E1=I*R1 and E2=I*R2 the adding the two equations together is

Etotal=E1+E2=I*R1+I*R2=I*(R1+R2)

Remember E is Emf (voltage)
I is current (ampere)
& R is resistance (ohms)

Chemistry/balancing reactions

Remember the algebra used in balancing reactions involves only whole numbers, In math these are called Diophene equations.

All electrons on the left and right side of the two half cells have to cancel, along with all elements. To get it create a table with a bar down the middle let one side be reactants (oxidation half cell) and the other products (reduction half cell). Label your electrons and elements and count them for various coefficients. Recommendation--start with your electrons and most abundant element (usually oxygen).

Then make sure you've reduced the coefficients---personally I don't like fractional coefficients so the reaction of oxygen and hydrogen is

2H2+O2->2H2O
if preferable to
H2+1/2O2->H2O
even though both are correct

As for balancing reactions it takes practice, and like all things requiring practice it becomes easier over time.

Too bad I can't do that with spelling.

Rap

ok thanks raprap i get it now. how do you know all this stuff

Too much education.

Rap