[needsomehelpplease]

In the reaction below 6.28g sample of hydrogen gas completely reacts with an excess of carbon.
C(s) +2H2(g) --> CH4(g)           enthalpy = -75.0 kJ
A. Determine the change in energy (heat).

I'm not sure how to do this problem! Does anyone think they can help me?

[DrCMS]

How many moles is 6.28g of hydrogen?
How many moles of hydrogen are in the balanced equation you have a heat output for?

[Polytriazole]

When doing thermochemistry, it can help to think of heat evolved or absorbed as if it were another product or reactant in the equation.  How would you do this problem if you were asked how much methane would be produced from 6.28 g hydrogen?

[Vidya]

Convert grams of hydrogen to moles of hydrogen as suggested by Borek and then from balanced equation you know that two moles of H2 gas gives 75KJ of heat.Now use mathematics to calculate amount of heat liberated from number of moles calculated by you.

[Nisarg Shah]

In the reaction below 6.28g sample of hydrogen gas completely reacts with an excess of carbon.
C(s) +2H₂(g) --> CH₄(g)           enthalpy = -75.0 kJ
A. Determine the change in energy (heat).

As far as I know,

    ΔE = ΔH + ΔnRT
=>ΔE = -75x10³ + (-2) x 8.314 x T (R=8.314 when ΔH is given in terms of J)

I don't know whether it applies in this case because temperature is not given. Please correct me if I'm wrong.

[Polytriazole]

I don't think you need that equation.  I think you only need stoichiometry here.  The enthalpy value given in the problem is what we call a "molar heat of reaction".  It tells you that making one mole of the product in this equation gives off 75.0 kJ of energy (or heat).  This heat can be treated just like a chemical product, and you can use the stoichiometric relationship presented in the chemical equation to calculate the amount of heat produced.