Acetylene is used in blow torches, and burns according to the following equation: 2 C2H2(g) + 5 O2(g) → 4 CO2(g) + 2 H2O(g) Use the following information to calculate the heat of reaction:?

Question

Acetylene is used in blow torches, and burns according to the following
equation:
2 C2H2(g) + 5 O2(g) → 4 CO2(g) + 2 H2O(g)
Use the following information to calculate the heat of reaction:

Hfo
(H2O(g))= -241.82 kJ/mol

Hfo
(CO2(g))= -393.5 kJ/mol

Hfo
(C2H2(g))=226.77 kJ/mol

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Answer 1 · 2016-05-05T17:33:04

$Delta"H"_(rxn)=-2511.04" ""kJ"$

Hess' Law states that the overall enthalpy change of a reaction is independent of the route taken.

Thermodynamics is concerned with initial and final states and the law is a consequence of the conservation of energy.

You can solve this problem by constructing a Hess Cycle.

Write down the reaction you are interested in. Below this write down the elements from which the reactants and products are made.

Then complete the cycle as shown:

MFCocs MFCocs

Notice I have multiplied the $Delta"H"_"f"$ values by the relevant stoichiometric numbers.

In energy terms the $color(blue)"BLUE"$ route must equal the $color(red)"RED"$ route since the arrows start and finish in the same place.

So we can write:

$(2xx226.77)+Delta"H"=(4xx-393.5)+(2xx-241.82)$

$:.453.4+Delta"H"=-1574-483.64$

$Delta"H"=-2511.04" ""kJ"$