Assume that our dye compound, XA, undergoes the following equilibrium in aqueous solution: XA(aq) ⇄ X+(aq) + A−(aq) (Both X+(aq) and A−(aq) are colorless) If a solution initially contains 65.4 μM XA and no X+ or A− prior to equilibrium, what are the concentrations of all three species if the equilibrium mixture gives an absorbance of 0.223 measured at a wavelength of 500.0 nm? Report answer in units of μM. (Hint: ICE and you know some equilibrium information.)

a). in this case, dh> 0 and sd> 0. if t becomes larger, the term "-tds" will become more negative. at some point, it is possible that -dts will be more negative than the dh is positive, and the reaction will become spontaneous. this is probably the correct answer, but you should look at all of the other possibilities and make sure of that.

5 structural isomers

the isomers are:

n-exane :   ch3ch2ch2ch2ch2ch3

2-methylpentane :   ch3ch(ch3)ch2ch2ch3

3-methylpentane :   ch3ch2ch(ch3)ch2ch3

2,3-dimethylbutane :   (ch3)2chch(ch3)2

2,2-dimethylbutane :   (ch3)3cch2ch3