[Violet89]

What is the heat change in J associated with 33 g of liquid acetic acid at 80 oC changing to solid at -3 oC?

c(acetic acid) (liq) = 2.18 J/(g*K)

c(acetic acid) (s) = 1.32 J/ (g*K)
ΔHfus(acetic acid) = 192 J/g
The freezing point of acetic acid is 17°C.

I keep getting 5.51E3, but the correct answer is -1.17E4. What am I doing wrong?

[Dan]

What am I doing wrong?

No idea. You'll have to show us what you did...

[Violet89]

What am I doing wrong?

No idea. You'll have to show us what you did...

For (s) - (33)(1.32)(17+3) = 871 J
For (l-s) - (33/60)(192) = 106 J
For (l) - (33)(2.18)(80-17) = 4532 J

871 + 106 + 4532 = 5.5E3

[UG]

Can you explain why you did 33/60 for the liquid to solid calculation

[Dan]

For (l-s) - (33/60)(192) = 106 J

Mistake is here, check the units of ΔH_fus given in the question.

[Violet89]

Can you explain why you did 33/60 for the liquid to solid calculation

Q = ΔHfus * mol

= (192)(0.55mol) = 106 J

The molar mass of acetic acid is 60.05 g/mol. So, 33g * 60.05 g/mol = 0.55mol

[Violet89]

For (l-s) - (33/60)(192) = 106 J

Mistake is here, check the units of ΔH_fus given in the question.

Wow, I completely missed that. Thank you. Got it!