I shall assist you with this:
b. Asumming that fuel oil has the empirical formula CH2, a Hf = -30kj/mol and a bulk density of 0.90 g/cm3, how many barrels(bbl) of oil would be required to generate the same amount of heat released in part (a) 1 bbl = 159 L.
OK, so we want to produce around 7 million kJ of energy, if each mole of fuel burnt produces 30 kj then:
Moles of fuel required = 7,000,000 / 30
= ~ 233333 Moles
Now lets find out how many moles are in one barrel:
159 litres of fuel = 159,000 cm3 of fuel
Now each cm3 of fuel has a mass of 0.9 g, so lets work how many moles of fuel are in 1 cm3 of fuel
molecular mass of fuel = ~14 g/n
Therefore Moles of fuel in 1 cm3 = 0.9 / 14
= 0.064 n
So how many moles of fuel are in a Barrel?
Moles CH2 in one barrel = 0.064 x 159,000
= 10176 moles
We need 233,333 moles to produce that much energy, so:
Barrels needed = 233,333 / 10,176
= ~ 23 barrels
I was pretty lax with my decimal points here, but use what I have done with more accurate numbers for a more precise result.
Also, if your answer for 3a turns out to be wrong, just plug the correct value into what I have done and adjust the numbers that follow accordingly.