[granite350]

4.  Spontaneity.  1) Use thermodynamics to prove that the reaction shown below is non-spontaneous at room temperature (25 °C).  2) Calculate the temperature at which the reaction would just begin to become spontaneous. This topic is discussed on pages 779 - 783 [814 - 819] in the textbook.

MgCl2(s)  +  H2O(l)  ?  MgO(s)  +  2 HCl(g)

I got the first part of the question but can't seem to get the 2 nd part.  how would i go about this would i have to use the equation

change in G=change H-T*change in S

but how would i go about solving T if all the parts of the varibles of the equation were solved at 25 degrees C (298 K)

for part one i got change of H=141.78 the reaction is endothermic because it is positive

for change in G= 69.7 when g is a large positive number larger than 10KJ the reaction is non spontaneous.

how would i go about solving T???

[Albert]

Standard dH and dS of reaction are expressed in kJ/mol and in J/K*mol, so you can use them for working out the temperature:

0>dH-TdS

[granite350]

what does each variable represent???

in that equation albert

[granite350]

the formula I used was (change in H)/T-(change in S)<0

then i worked out the equation to 141.78Kj for H and .240 for S

this is what  did

[141.78KJ/Temperature]-.240Kj/K<0

T=590.75K

[Albert]

dH - TdS < 0

141.78 - T*0.24 < 0

141.78/0.24 < T

T = 590.75 K

In a nutshell, you solved the problem.