Question

Consider the following intermediate reactions.

2 equations. First: upper C upper H subscript 4 (g) plus 2 upper O subscript 2 (g) right arrow upper C upper O subscript 2 (g) plus 2 upper H subscript 2 upper O (g). Delta H 1 equals negative 802 kilojoules. Second: 2 upper H subscript 2 upper O (g) right arrow 2 upper H subscript 21 upper O (l). Delta H subscript 2 equals negative 890 kilojoules.

The overall chemical reaction is as follows.

Upper C upper H subscript 4 (g) plus 2 upper o subscript 2 (g) right arrow upper C upper O subscript 2 (g) plus 2 upper H subscript 2 upper O (l).

What is the correct enthalpy diagram using the Hess law for this system?
mc019-3.

mc019-4.
mc019-5.
mc019-6.

Answer 1

The correct enthalpy diagram using the Hess law for this system is mc019-5.

The correct enthalpy diagram for this system, utilizing the Hess law, involves breaking down the overall reaction into intermediate steps with known enthalpies. In the first step, the given reaction shows the combustion of methane (CH4) to produce carbon dioxide (CO2​) and water (H2O), with a corresponding enthalpy change of ΔH1 =−802kJ. The second step involves the phase transition of gaseous water to liquid water, with an enthalpy change of ΔH2=−890kJ.

To obtain the overall enthalpy change for the combustion of methane to produce liquid water, the two intermediate reactions are combined, leading to an enthalpy change of −802kJ−890kJ=−1692kJ. The correct enthalpy diagram, mc019-5, represents this sequence of reactions and demonstrates the application of Hess's law to determine the enthalpy change for the overall chemical process.