Question

During the combustion of 5.000 g of octane, C8H18, 239.5 kcal is released.
2C8H18(l)+25O2(g)→16CO2(g)+18H2O(g)

How much energy is released by the combustion of 1.010 mol of C8H18?
How many grams of octane must be burned to release 427.3 kcal ?
How many kilocalories are released by the combustion of 19.0 g of C8H18 ?

Answer 1

having trouble with these :/

Answer 2

@Photon336

Answer 3

Based on the information provided in the question, first calculate the enthalpy in kJ/mol.

This value gives you a way to answer all the questions!

Answer 4

@Cuanchi

Answer 5

I think it is not necessary to convert to the kcal to kJ/mol, you can just use conversion factors.

\[ \frac{5.000 g octane }{239.5 kcal } =\frac{ 239.5 kcal }{ 5.000 g octane } \]
a) calculate the molecular mass of octane C8H18= 12x 8 + 18 = MM g octane

1.010 mol of C8H18 x (MM g octane/ 1 mol) x (239.5 kcal/ 5.000 g octane) = _____ kcal

b) 427.3 kcal x (5.000 g octane/ 239.5 kcal) = ________ g of octane

c) 19.0 g of C8H18 x (239.5 kcal/ 5.000 g octane) = _______kcal

Answer 6

Sorry, misread the kcal as kJ. You're right, no conversion necessary!