practical (alcohols) Flashcards
what is the aim of the experiment?
to measure the enthalpy per mol of each alcohol through the combustion of different alcohols
how do you calculate the heat energy absorbed by the water?
q=mcΔT
why does methanol have a different enthalpy change than hexanol?
because there are more bonds to be broken and formed in hexanol, which releases more energy
this results in a higher enthalpy change
will methanol or butanol produce more heat/gram
butanol, because it has more bonds compared to methanol, releasing more energy
how does the alcohol structure affect its enthalpy change?
alcohols with long carbon chains have more compared to smaller alcohols
more energy is required to break and make these bonds during combustion
with longer carbon chains have a higher enthalpy change
why is complete combustion desirable when burning alcohols?
because it ensures maximum release of energy
minimizes production of harmful by-products like carbon monoxide
which chemicals would do complete and which would do incomplete combustion?
smaller alcohols need less oxygen to achieve complete combustion - can more easily react with all oxygen
larger alcohols have more C-H and C-C bonds, so more oxygen is required. more likely to do incomplete combustion
what are the differences in the flames of hexanol and ethanol?
hexanol - orange color, transparent/less opaque
ethanol - yellow, stronger, more opaque
how would the enthalpy change with chain length?
the enthalpy change of combustion will increase as the chain length increases
why does increased chain length = increased enthalpy?
because longer alcohols have more carbon and hydrogen atoms, which means they release more energy when combusting
do alcohols that do complete combustion or incomplete have a higher enthalpy?
alcohols that do complete combustion will have higher enthalpy than incomplete combustion
complete combustion makes more carbon dioxide and water - more energy release
what does a blue vs. orange/yellow flame mean?
blue flame usually means complete combustion
yellow/orange flame usually means incomplete combustion
how will temperature change vary with enthalpy change?
alcohols with higher enthalpy change - greater increase in water temp for same amount of alcohol burned
larger alcohols that take longer to combust will lose more heat to the environment, which means more skewed results
what is the problem for the results with incomplete combustion?
solution?
it can produce carbon monoxide + soot - affects the accuracy of the enthalpy, since not all energy from alcohol is released
provide good ventilation + oxygen supply
