if 11.0 mol ethane burns completely, how much thermal energy would be produced
From the NIST webbook, we see that the heat of combustion for ethane is approximately 1560 kJ/mole (Source: http://webbook.nist.gov/cgi/cbook.cgi?ID=C74840&Units=SI&Mask=1#Thermo-Gas )
If we have 11.0 moles of ethane that is completely burned, then we simply multiply the number of moles we have by the heat of combustion:
11.0 mole *(1560 kJ/mole) =17160 kJ or 17.160 MJ. Now, taking into account significant figures, we have 17.1 MJ or 1.71x10^3 kJ.
Keep in mind that 1 MJ = 1000 kJ