Most likely the sources of error, ie. why the experimental value of the molar heat of combustion of the fuel was lower than the theoretical value.
They might also ask you how to minimise these losses.
Physical sources of error:
- Heat lost to atmosphere by convection (minimised by enclosing apparatus inside a cardboard box, so minimal heat is lost to surrounding)
- Stirring water can also make the heat of water uniform throughout, so that heat will be evenly distributed, thus measurement of temperature will be more accurate
- Lower distance between the spirit burner and the beaker of water, so that heat transfer is more efficient
- Put a lid on the spirit burner immediately after the prac, so that no excess fuel is vaporised
Chemical sources of error:
- Incomplete combustion: not enough oxygen gas, so that the heat released is less than the heat that would be released when the fuel undergoes complete combustion. (the theoretical value assumes complete combustion)
They might also ask for safety precautions.
You might wanna mention that the heat released is high, so keep distance from apparatus to prevent being burnt. Equipment is fragile, so extra care needs to be taken when handling. The electronic balance is sensitive to heat, so to prevent breaking it, wait until the spirit burner has cooled down before weighing it.
