Question

C8H18(l)+252O2(g)→8CO2(g)+9H2O(g)

ΔH∘rxn=−5074.1 kJ

What mass of octane (in g) is required to produce 5010 kJ
of heat?

Answer 1

112.787g

Step-by-step explanation:

First, identify a mole of reaction to use. In this case, octane (C8H18) fits nicely as it has a 1:1 mole Octane to mole Rxn ratio. Find the molar mass of octane to be 114.23 g/mol.

Now, find the ratio of Enthalpy of reaction to desired heat:

5010/5074.1=0.98737.

To find the mass needed, let 0.98737 be the number of moles:

0.98737mol*114.23g/mol=112.787g

Double check anwser:

112.787g*1mol C8H18/114.23g * 1mol Rxn/1 mol C8H18 *-5074.1 kJ/1 mole Rxn * -1 exothermic coefficent = 5010 kJ.

Exothermic coefficent converts heat released by the system into heat released to the surrounding for an anwser which fits the point of view of the surrounding rather than the system (anwsers the question of how much energy released/produced rather than lost in/by the reaction).