Help with Unit 3 Chemistry?

[simrat99]

Can anyone please help me with the following questions?
1. Calculate the energy released, in kJ, when 3.56 g of carbon undergoes combustion according to the thermochemical equation:
2C(s)+O2(g)→2CO(g)      ΔH=−788 kJ mol−1
2. The use of hydrogen as a renewable and environmentally friendly fuel is currently the subject of much research. The main product of hydrogen combustion is water. The production of liquid water from the reaction between gaseous hydrogen and gaseous oxygen can be represented by the following thermochemical equation.
O2(g)+2H2(g)→2H2O(l)      ΔH=−572 kJ mol−1
Calculate how much energy, in kilojoules, would be released or absorbed by the following reactions.
a). 2O2(g)+4H2(g)→4H2O(l)
b). H2O(l)→1/2O2(g)+H2(g)

[sweetcheeks]

1) Referring to the equation it shows us that the complete combustion of two moles of carbon will net an energy output of 788kJ.
2C(s)+O2(g)→2CO(g)      ΔH=−788 kJ mol−1

To determine how much energy will be released by 3.56 grams of Carbon you must first find the moles of carbon. Next you will need to use stoichiometry to ratio the moles of carbon, to the amount of energy released (2 moles of carbon releases 788kJ of energy). This is the same process as working out yield type questions.

2) O2(g)+2H2(g)→2H2O(l)      ΔH=−572 kJ mol−1
Some background info. The delta H is represented per reaction, that is the complete combustion between 1 mole of oxygen gas and 2 mole of Hydrogen gas, yielding 2 mole of water, will release 572kJ of energy.

a) when you double the coefficients of each molecule, the delta H will be doubled, as the delta H now indicates how much energy the complete combustion between 2 moles of oxygen gas, 4 moles of hydrogen gas, yielding 4 moles of water. It will now be -1144kJ/mole
b) Using the information I have provided, attempt to work out the delta H if you halve the amounts of everything

[simrat99]

Thanks a lot!