State hess's law.how is it used

2 answers:

5 0

Hess' Law states that the enthalpy change in a reaction can be calculated from the enthalpy changes of reactions that, when combined, result in the desired reaction.

For example, to check the enthalpy change that occurs when benzene undergoes incomplete combustion to water and carbon monoxide is not an easy task, because the products invariably contain CO2. However, by combining the reactions of the complete combustion of benzene and the combustion of CO, you can get the reaction you want.

Reaction wanted: 2C6H6 + 9O2 → 12CO + 6H2O
Reactions provided: 2C6H6 + 15O2 → 12CO2 + 6H2O and 2CO + O2 → 2CO2, and their associated ΔH.

Rearrange the reactions so that, when they add up, they result in the wanted reaction.

2C6H6 + 15O2 → 12CO2 + 6H2O (leave as is; no changes to ΔH)
12CO2 → 12CO + 6O2 (reverse and multiply by 6; this changes the sign of ΔH and multiplies it by 6)

Added up, it will result in 2C6H6 + 9O2 → 12CO + 6H2O. Add up the ΔH values for the rearranged reactions to find ΔH for this particular reaction.

PSYCHO15rus [73]3 years ago

5 0

Answer: Hess's Law says the total enthalpy change does not rely on the path taken from beginning to end. Enthalpy can be calculated in one grand step or multiple smaller steps.

To solve this type of problem, organize the given chemical reactions where the total effect yields the reaction needed. There are a few rules that you must follow when manipulating a reaction.

The reaction can be reversed. This will change the sign of ΔHf.

The reaction can be multiplied by a constant. The value of ΔHf must be multiplied by the same constant.

Any combination of the first two rules may be used.

Finding a correct path is different for each Hess's Law problem and may require some trial and error.

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What type of chemical bond holds the na+ and cl- ions together in table salt?

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The bond between Na + and Cl- ions is an ionic bond

To achieve stability, atoms with low ionization energy such as Na atoms will release electrons and bind to atoms with high-affinity energy such as Cl atoms

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Atoms have different stability. Unstable atomic atoms will try to form stable electron configurations like those of noble gases. Where noble gases have the number of outer electrons 2 or 8

The formation of electron configurations such as noble gases can be done by forming shared ions or electron pairs

Atoms with high ionization energy and atoms that are difficult to draw electrons will form bonds with shared electron pairs (electrons can be from one atom or two atoms attached)

In forming ions, atoms will release or attract electrons

Ion bonds occur because atoms that have low ionization energy (easily release electrons) form a + ion, and these electrons are bound by atoms that have large affinity energy (easily pulling electrons)

Generally, ionic bonds occur in metal and nonmetallic elements. Metal elements have low ionization energy and non-metallic elements have a high electron affinity

In Na atoms, to achieve stability, Na will release one electron so that it has an electron configuration like noble gas Ne

Na: 2 8 1

Ne: 2 8

so that it becomes a Na + ion

While the Cl atom will bind one electron, so it has an electron configuration like noble gas Ar

Cl: 2 8 7

Ar: 2 8 8

So that it becomes a Cl- ion

Finally, there will be an attractive attraction between positive ions and negative ions and NaCl is formed

So the bond between Na + and Cl- ions is an ionic bond

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