Chemistry- Enthalpy

Question

The combustion of hexane is given by the following reaction.

2 C₆H₁₄ + 19 O₂  12 CO₂ + 14 H₂O

The enthalpy of reaction is −4163.0 ^kJ/_mol. How much energy (in joules) will be released if 58.53 grams of hexane is burned. (Molar mass of hexane = 86.20 ^g/_mol). 

Answer 1

Convert 58.53 g of hexane to moles of hexane:

58.53 g x 1 mol / 86.20 g = 0.6790 mols C₆H₁₄

Use the molar enthalpy of combustion value (4163.0 kJ/mol) to find energy released by 0.6790 mols C6H14:

4163.0 kJ/mol x 0.6790 mol = 2827 kJ x 1000 J / kJ = 2826687 J

Rounded to 4 sig.figs. answer should be 2,827,000 J of energy released.

You can put a negative sign (energy released) or omit the negative sign and state "energy released".