Molar heat of combustion question (1 Viewer)

[chingyloke]

Hey guys. can anyone help me with this question?

The heat of combustion of ethanol is 1360kJ/mol. What madd of ethanol needs to be burnt to raise the temperature of 350g of water through 77 degrees celsius is 50% of the heat released by the ethanol is lost to surroundings? The specific heat capacity of water is 4.2 joules per kelvin per gram.

 

[xFusion]

using deltaH=-mCdeltaT
deltaH=350*4.2*77
=113190j/g
deltaH/mass of ethanol burnt *molar mass =molar heat of combustion (1360kj/mol)
113.190/(1360/46)=mass of ethanol (if no heat loss)
therefore i think you would double this value since 50% is loss.
hence:7.66g?
[ok.. this issnt really making sense.. since number seems too small. the number should be right but i dunno about the units]

 

[chingyloke]

nah man that is spot on. thanks heaps for you help.

 

[xFusion]

great ^^ thats my molar heat of combustion revision for tomorrows chem half yearlys.