ARGHHHHH!

[lacoste]

Found a really annoying question.

For the reaction

H2O <=> H+ + OH- , Kw= 10^-14 at 25*C

55.9 kJmol^-1 of heat is evolved when one mole of H+ reacts with one mole of OH-. At 80*C the Kw and the pH of pure water is?

Kw greater or less than 10^-14

pH greater or less than 7



Thanks!!!!!!!!!!!

[sir0004]

It says heat is evolved. Thus, it is an exothermic reaction. For exothermic reactions, as temperature increases, net backward reaction occurs and Kw value decreases.

Since reaction proceeds net backward, the concentration of hydrogen ions decreases. Thus, the pH increases. Since the pH of pure water is originally at 7, now it increases so it is more than 7.

[lacoste]

answer is

Kw greaterthan 10^-14

pH less than 7


? hmm

[IntoTheNewWorld]

it's an endothermic reaction,as shown by "55.9 kJmol^-1 of heat is evolved when one mole of H+ reacts with one mole of OH-" Which means that heat is given off in the back reaction, the back reaction is exothermic which means the forward reaction is endothermic

 hence when the temperature increases a net forward reaction occurs and the concentration of hydrogen ions increases, making it more acidic and the pH becomes less than 7. The Kw increases as the concentrations of H+ and OH- (the products) have increased.

[lacoste]

wait, so the equation in the question is an endo?

it said heat evolved so i thought it was exo?

[lacoste]

nvm, gottt it!!

thx

[thisongaintgottaname]

it's an endothermic reaction,as shown by "55.9 kJmol^-1 of heat is evolved when one mole of H+ reacts with one mole of OH-" Which means that heat is given off in the back reaction, the back reaction is exothermic which means the forward reaction is endothermic

 hence when the temperature increases a net forward reaction occurs and the concentration of hydrogen ions increases, making it more acidic and the pH becomes less than 7. The Kw increases as the concentrations of H+ and OH- (the products) have increased.

(y)