Question

How many moles of isooctane must be burned to produce 100 kJ of heat under standard state condaitions?

Answer 1

Answer:

0.018 moles of isooctane must be burned to produce 100 kJ.

Explanation:

When the isooctane is burned, it undergoes a reaction known as combustion, in which reacts with oxygen to produce carbon dioxide and water. In standard conditions (Pressure = 1 atm and Temperature = 298 K) formed water is liquid. The balanced equation is:

C₈H₁₈(l) + 12.5 O₂(g) ⇄ 8 CO₂(g) +  9 H₂O(l)

The standard enthalpy of combustion (which can be found in tables) relates the amount of isooctane that reacts and the heat the reaction liberates. In this case, ΔH°c = -5,460 kJ/mol, that is every 1 mol of isooctane that burns, 5,460 kJ of heat are released.

We can begin with the information of 100 kJ and apply this conversion factor. Since this energy is released, by convention, we write it with a minus sign.

$-100kJ.\frac{1mol (isooctane)}{-5,460kJ} =0.018 mol(isooctane)$