Heat Evolved During Combustion?

Question

C(s,graphite) + O2(g) --> CO2(g)
How much heat is evolved when 3.747×101 moles of C(s,graphite) is burned in excess oxygen.
Answer to 4 sig figs.

How much heat is evolved when 1.201×102 g of C(s,graphite) is burned in excess oxygen.
Answer to 4 sig figs.

any idea how to do these two questions?need serious help..step by step solutions please..thank you so much!

Answer 1

OK, you must have left something out. There is not enough information to work the problem. You can give the answers to four sig figs because you have four sig figs for the mass or the moles, however you will have to have other measurements to at least four sig figs also. There has to be either some heat shown in the equation on the product side (usually as a number of Joules or kiloJoules) or there will be a Delta H shown, possibly subscripted as comb for combustion. The heat (or enthalpy) of combustion for graphite is -393.5 kJ/mole

C(graphite) + O2(g) -> CO2(g) + 393.5 kJ

or the equation will be followed by the symbol delta then H subscripted comb and the number -393.5 kJ which means that there are 393.5 kJ of heat produced for the reaction (which incidentally involves 1 mole of C(graphite)). These numbers are from Chemistry The Central Science by Brown, LeMay and Bursten. Your book may have a different value since it is a measured value. Once you have this value, you can simply multiply the heat of combustion per mole times the number of moles to get the total heat. If you have grams such as in the second problem, you will have to divide by the molar mass of carbon (12.01 g/mole) to get the moles to multiply the heat of combustion by. You will really have to get the enthalpy of combustion from your text since it is problbly different from what I have posted. Good luck, e-mail me if you need more help.