Slandard entropy change of combustion?

Question

I want to work out the standard entropy change of combustion for alcohols. I have the mass of the alcohol at the start and at the end of the experiment but I am now stuck. How do I work it out!

Answer 1

Standard Enthalpy of Combustion - The enthalpy change when one mole of a substance is completely combusted in excess oxygen.

As with the hydrocarbons, the combustion products of the alcohols are carbon dioxide and water e.g.
C2H5OH + 302 --> 2CO2 + 3H20

To work out the enthalpy of combustion for a substance, like an alcohol, you need to know the change in mass but also the amount of energy transferred e.g. to a set volume of water. We can then use a formula like Q=mcΔT (Q is the energy transferred (Joules), m is the volume of water (at 1g/cm3), c is the specific heat capacity of water (4.18J g-1 K-1) and ΔT is the temperature change in the volume of water.

If say, 0.18g of ethanol was combusted in an experiment, work out the number of moles used (n=m/M) and then scale answer (from the Q=mcΔT equation) to get a figure in kJ mol-1. This should be something around -1121.6kJ mol-1.

Answer 2

Entropy = Energy released or absorbed divided by temperature in Kelvin.