# Gchem simple questions

#### grifgin

##### Member
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7+ Year Member
for KSP
ie for the RX dsfiojnfoids ---> 2X + Y

sometimes the KSP = [2X]^2 [y]
whiile sometimes its given simply as = [X]^2 [y]

any reason for this???

also to fiind overall E for a redox RX, we do this rite?
[1] (the highest positive) + (the other which is negative)
in between the two is POSITIVE sign???
right?

THANKS

#### 714guy

##### counting down till 5/2012
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grifgin said:
for KSP
ie for the RX dsfiojnfoids ---> 2X + Y

sometimes the KSP = [2X]^2 [y]
whiile sometimes its given simply as = [X]^2 [y]

any reason for this???

2 A + B --> C + 3 D

Ksp= [A]^2/[C][D]^3

Rate law = K [A]^2

you probably got them mixed up.

also to fiind overall E for a redox RX, we do this rite?
[1] (the highest positive) + (the other which is negative)
in between the two is POSITIVE sign???
right?

E = Ecell reduced + Ecell Oxidized

however most of time when you're given the Ecell, its the standard reduction potential, so for Ecell oxidized you must reverse the reaction making the Ecell a negative.

A2+ + B --> A + B2+

standard reduction potential for A is Ecell = -.24

standard reduction potential for B is Ecell = .45*

*since this is for reduction, you must reverse the rxn so its oxidized, that will make it a negative so Ecell = -.45

E = (-.24) + (-.45) = -.69

THANKS
good luck

OP
G

#### grifgin

##### Member
10+ Year Member
7+ Year Member
hey thanks!

theres a question and its answer does not have the reactants in the ksp equation at all?

or maybe its QSP

#### keibee82

##### Blue_tooth...
10+ Year Member
grifgin said:
hey thanks!

theres a question and its answer does not have the reactants in the ksp equation at all?

or maybe its QSP
Yes, Ksp is the solubility product which measures how much of the
reactants are soluble. Therefore Ksp has only the product side.
A + B ---> 3C + D

Ksp = [C]^3 [D]

one that 714guy wrote was Kp not Ksp.

#### vize

##### Member
10+ Year Member
ksp will sometimes be [2x]^2 [y] only if the reactants are something like MgCl2. MgCl2 -> 2Cl + Mg... so the solubility constant is going to be ksp = [2Cl]^2 [Mg] ... this is because once it fully dissociates there's going to be 2Cl for every 1 Mg... hope that helps

#### caroochy

##### Bigger than yours
10+ Year Member
5+ Year Member
vize said:
ksp will sometimes be [2x]^2 [y] only if the reactants are something like MgCl2. MgCl2 -> 2Cl + Mg... so the solubility constant is going to be ksp = [2Cl]^2 [Mg] ... this is because once it fully dissociates there's going to be 2Cl for every 1 Mg... hope that helps

why?? what is the difference between MgCl2 and another molecule that will have its ksp be [x][y]^2 instead of [x][2y]^2

#### vize

##### Member
10+ Year Member
not sure i've never seen anything like that before