heat combustion prac (1 Viewer)

[nicky]

i have absolutly no idea on how to do the calculations for the heat combustion of ethanol. but i also have to compare it to 1-propanol and 1-butanol per gram and mol. can anyone help?
here are my results:
ethanol, 1-propanol, 1-butanol
initial mass (g) 243.35, 241.15, 247.66
final mass (g) 242.64, 240.58, 247.1
initial temp 22, 22, 22
final temp 33 33, 32, 32

 

[nicky]

the table didnt come out very well..... i haope u can understand my results.

 

[Frigid]

the heat of combustion is given by the equation:

delta-H = m x C x delta-T

where delta-H is the energy in joules;
m is the mass of water in grams;
C is the specific heat of the substance (water is 4.2 J/K/g);
delta-T is the temperature change.

now, basically what i need to know is what mass of water did you heat up? plug that value as 'm' into the equation and you should get a delta-H value for a certain mass of ethanol burnt (initial mass - final mass).

by division we can work out joules per gram (eg. 1000 Joules /10 grams = 100 Joules/gram).

now multiply joules/gram values by the respective molar mass (ethanol is 46 grams/mole). for example for ethanol, supposing 100 J/g: 100 J/g => (100 x 46) => 4600 J/mol

now work it out for the other two alkanols. now explain why the combustion values are higher as the chain length increases.

 

[Kirsti]

thankyou! i have a prac test on that tomorrow and my lab partner is too sick to get out of bed. Must make sure I can remember that incase my new partner doesn't.
Thankyou

 

[Frigid]

no worries. glad i can help.