Thermochemistry Question

[Rosalina]

                    A student wished to determine whether fats or sugars had the higher energy content. Small samples of stearic acid, C₁₈H₃₆O₂(s) (a fatty acid) or sucrose, C₁₂H₂₂O₁₁(s) (a sugar) were burned and the data collected as shown below.

Sucrose                Stearic Acid      Mass of sample                                        1.55 g                      1.17 g      Calorimeter constant (heat capacity)       8.57 kJ/°C               8.57 kJ/°C      Initial temperature of calorimeter          24.30°C                   26.40°C      Final temperature of calorimeter           27.88° C                   30.28°C

a.         Use the data collected to calculate the enthalpy of combustion for 1.00 g of each   substance.

 

So, for this question, I was planning to use Hess's Law (products- reactants) to get the enthalpy of combustion. After that could I just plug it in the formula n Δ Hm = mc Δ t?

Thank you

[FChaosi_]

Stricly, Hess's Law involves multiple reactions.
For each substance listed in the question, there is only one reaction, so Hess's Law isn't needed.
You can just use the equation:

Q = mcΔt

The specific heat capacity is given, as are the masses and changes in temperature, so all you have to do is plug in the values and compare the heat produced. By the way, the heat produced will be the negative of Q, as Q is the energy taken in by the environment.