VCAA sample exam

[strahk]

Going through the sample exam, I'm not sure how to find two multi choice answers -
Q 25 - I assumed that considering the silver half equation is doubled to balance electrons, that its E nought value would be too (ie. +0.80 to +1.60) which would mean option C would give the voltage for the cell (1.60-0.34=1.26V) , however the correct answer is A which is the same process except the E nought value for Ag is not doubled even though the equation is. So my question is, unlike deltaH do E nought values not get doubled, halved, etc according to the molar ratio in the full equation?

Q 28 - not sure how to find this answer in coulombs... all I know is (from data book) that the enthalpy of combustion for methane is -889kj/mol and not sure how to convert this to coulombs.

Help please!!

[barydos]

no need to double, just do higher E0 minus lower E0 value.

1 mol methane --> 8 mol of n(e-) (from equation)
Q = n(e-)*F
 = 8 * 96500
rounds to C

[strahk]

Thank you so much!!
So obvious now