[hillkr]

Problem:
Phthalates used as plasticizers in rubber and plastic products are believed to act as hormone mimics in humans. The value of ΔH_comb for dimethylphthalate (C₁₀H₁₀O₄) is 4685 kJ/mol. Assume 0.930 g of dimethylphthalate is combusted in a calorimeter whose heat capacity (C_calorimeter) is 6.894 kJ/°C at 21.447°C. What is the final temperature of the calorimeter?
Scratch work:
C₁₀H₁₀O₄ = 194.075 g/mol 0.930 g = 0.00479 g/mol
ΔH_comb = 4685 kJ/mol
C_p = 6.894 kJ/°C
initial heat = 21.447°C
heat released = 4685 × 0.00479 = 22.45 kJ
What I did and got it wrong:n·C_p·ΔT
0.00479·6.894·(22.45-21.447) = 0.033121

How do I work this problem?

[Borek]

C₁₀H₁₀O₄ = 194.075 g/mol 0.930 g = 0.00479 g/mol

Nothing makes sense here, but surprisingly the number is the one needed later.

heat released = 4685 × 0.00479 = 22.45 kJ

OK

n·C_p·ΔT

Nope, that's not the correct equation. What is the definition of the heat capacity? How does it differ from the specific heat capacity? When do we use one, when the other?

[hillkr]

For C₁₀H₁₀O₄ 194.075 is the molecular weight and the problem said 0.930 g of C₁₀H₁₀O₄ so i divided 0.930 by 194.075 to get the mols for the problem which was equal to 0.00479g/mol.

Heat capacity (C_p) is the quantity of energy needed to raise the temperature of an object by 1°C.
Specific heat (c_s) is the energy required to raise the temperature of one gram of a substance by 1°C
So heat capacity is raising the temperature of the whole thing and specific heat is 1 gram.
I assumed I would use the heat capacity equation because the problem gave the heat capacity. My teacher did not go over one of these problems in class so i really do not know how to do it. 

[mjc123]

For C10H10O4 194.075 is the molecular weight and the problem said 0.930 g of C10H10O4 so i divided 0.930 by 194.075 to get the mols for the problem which was equal to 0.00479g/mol.

The unit for moles is moles, not g/mol, which is the unit of molecular weight. g divided by g/mol gives mol. But the number is correct.

Heat capacity (Cp) is the quantity of energy needed to raise the temperature of an object by 1°C

Correct. An object. Not a mole of objects, or a mole of something else, like dimethyl phthalate. So why multiply by 0.00479?

0.00479·6.894·(22.45-21.447) = 0.033121

Why do you subtract a quantity in °C from a quantity in kJ? The final temperature is an unknown, it's what you're trying to find. You know the heat, you know the heat capacity. So...

[hillkr]

So it is heat/heat capacity to get the temperature change then you add that to the temperature given.
22.45 ÷ 6.894 = 3.256
21.447 + 3.256 = 24.70°C

Thank you so much for helping me.