determine G° for the solid dissolving in water. Suppose you use the same solid a
ID: 921215 • Letter: D
Question
determine G° for the solid dissolving in water. Suppose you use the same solid as in Question #3 (that is, the molar mass is 95.8 g/mol) and obtain the following data:
Mass of solid 2.968 g
Volume of solution 5.37 mL
Volume of water 2.86 mL
Temperature of solution 25.4 °C Part 1:
Determine the concentration of the solid. 5.77 M You are correct.
Determine G° if we assume K = [solid] in the saturated solution in KJ/mol:
I know the formula should be Delta G = -R * T* In(K) -R = 8.3145 J/Mol K T = 298.4 K
What is In (K) and how do I get that and the Delta G? Moles of the solid = mass/molar mass = 2.968/95.8=0.30 moles Molarity = moles/volume of solution =( 0.30/5.37 )x1000 = 5.7693 M G° = -2.303RTlogK = -2.303x8.3145x298.4log(5.77) =5713.8x0.76 =4349.2 Joules =4.3492KJ
This answer comes back as correct but ... where does the -2.303 come from in the formula? I have a follow-up problem that takes into account of the water added to the solution. and can't seem to get that correct.
Explanation / Answer
The question is not very clear but I can see you are asking one thing clearly
where does the -2.303 come from in the formula?
The actual equation is
G° = –RT ln K in converting this to log K you need to put in the factor of -2.303
In the equation G° = –RT ln K; K is the equilibrium constant not sure why you put the concentration term there and how you ended up with the correct answer.
You will need the formula for the solid and put up the equation
Solid + water = ions from the solid (Aq)
Enthalpies of solution may be either positive or negative - in other words, some ionic substances dissolved endothermically (for example, NaCl); others dissolve exothermically (for example NaOH).
So I guess since you put in the wrong term for K in this case in the other case you are not getting the correct answer
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