Please Help, Specific Heat, Thermochem problems!!?

Question

∴Through the use of a ground-based spectrometer, the atmosphere of a planet has been determined to contain sodium at a concentration of 87.0 x 105 atoms per cm3. Express this in moles per liter.


∴A 1.05-g sample of caffeine C8H10N4O2 burns in a constant-volume calorimeter that has a heat capacity of 7.85 kJ/K. The temperature increases from 297.50 K to 302.52 K. What is the molar heat of combustion of caffeine (in kJ)?

Answer 1

When you say "at a concentration of 87.0 x 105 atoms per cm3", do you mean "at a concentration of 87.0x10^5 atoms per cm^3"?
87.0x10^5 atoms /cm^3 = 87.0x10^8 atoms /L
<==> (87.0x10^8 atoms /L)*(1 mol/ 6.022x10^23 atoms) = 1.44x10^(-14) mol/L

(7.85 kJ/K)*(302.52K - 297.50K) = 39.4 kJ
The molar mass of caffeine C8H10N4O2 is: 194.19 g·mol−1.
Hence the molar heat of combustion of caffeine is:
39.4 kJ*(194.19 g/mol)/(1.05g) = 7.29x10^3 kJ/mol