We are asked to calculate the ΔH° for 2 CH4(g) → C2H4(g) + 2 H2(g) using the thermochemical data.
Modify the reactions such that when they add up, it will result to the target equation.
2 CH4(g) +
4 O2(g)⟶ 2 CO2(g) + 4 H2O(l) 2Eqn1 (multiplied by 2) C2H6(g) → C2H4(g )+ H2(g) -Eqn2 (reversed) H2O(l) → H2(g) + 1/2 O2(g) - (1/2)Eqn3 (reversed and multiplied by 1/2) 2 CO2(g)+ 3 H2O(l) ⟶ C2H6(g) + 7/2 O2(g) - (1/2)Eqn4 (reversed and multiplied by 1/2)
2 CH4(g) → C2H4(g) + 2 H2(g)
We can use Hess' law to calculate enthalpy changes that cannot be measured. One such reaction is the conversion of methane to ethylene: 2 CH4(g) → C2H4(g) + 2 H2(g)
Calculate the ΔH° for this reaction using the following thermochemical data:
|ΔH°rxn = - 890.3||CH4(g) + 2 O2(g)⟶ CO2(g)+2 H2O(l)|
|ΔH°rxn = - 136.3||C2H4(g )+ H2(g)⟶ C2H6(g)|
|ΔH°rxn = - 571.6||2 H2(g) + O2(g) ⟶ 2 H2O(l)|
|ΔH°rxn = - 3120.8||2 C2H6(g) + 7 O2(g)⟶4 CO2(g)+ 6 H2O(l)|
Frequently Asked Questions
What scientific concept do you need to know in order to solve this problem?
Our tutors have indicated that to solve this problem you will need to apply the Hess's Law concept. You can view video lessons to learn Hess's Law. Or if you need more Hess's Law practice, you can also practice Hess's Law practice problems.