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:?

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

Answer 1

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

Explanation:

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:

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"`