um, just wondering, is it possible that the experiment results given in a question lead you to a different molar heat of combustion value to the one on the data book?
There could be. I guess someone like TT would be able to answer that question efficiently since he's swallowed many questions by now.

I know for a fact that in physics, if a question asked you calculate the value for the speed of sound, it will be different to the real value but somewhere close. Hence, if you just write

without any working, you'll receive no marks.
EDIT: Actually you said:
is it possible that the experiment results...
Since it's an experiment, you would expect the value for the molar heat of combustion would be similar to the actual value since you've got sources of error/uncertainty, wouldn't you?