# KJ per hydrocarbon "empirical formula unit"

• Ritzycat
In summary, the conversation discusses the calculation of the value of ΔH∘f per empirical-formula unit of a hydrocarbon, based on the combustion of a sample of the hydrocarbon. The calculations involved determining the empirical formula of the hydrocarbon and using the mass and heat values to find the molar value of ΔH∘f. The final answer of 627.266 kJ/mol was not correct, possibly due to significant figures or rounding errors.
Ritzycat

## Homework Statement

A sample of a hydrocarbon is combusted completely in O2(g) to produce 19.65gCO2(g), 4.023gH2O(g), and 280kJ of heat.

Calculate the value of ΔH∘f per empirical-formula unit of the hydrocarbon.

None I know of

## The Attempt at a Solution

Previous calculations found that the hydrocarbon had a mass of 5.811g.

Per empirical formula unit: (I determined the empirical formula to be CH, which was correct)

molar mass of CH = 13.018g/mol

5.811g / 13.018g/mol = 0.447 mol CH

280kJ/0.447 mol = 627.266 kJ/mol

My final answer was 627.266 kJ/mol but that was not correct.

Am I interpreting the meaning of "empirical-formula unit" correctly?

Any help is greatly appreciated.

Looks OK to me, perhaps it is just a matter of significant figures, or some rounding error?

## 1. What is the definition of a "KJ per hydrocarbon empirical formula unit"?

A "KJ per hydrocarbon empirical formula unit" is a unit of measurement used to describe the energy content of a hydrocarbon compound. It represents the amount of energy, in kilojoules (KJ), released when one mole of the compound undergoes complete combustion.

## 2. How is the energy content of a hydrocarbon compound determined?

The energy content of a hydrocarbon compound can be determined by measuring the heat released during combustion and converting it to a per mole basis. This value is then divided by the number of moles of the compound present in one empirical formula unit.

## 3. Why is the energy content of hydrocarbon compounds important?

The energy content of hydrocarbon compounds is important because it is a measure of the potential energy that can be released when the compound is burned. This information is essential for understanding the efficiency and potential uses of different hydrocarbon fuels.

## 4. How does the empirical formula of a hydrocarbon compound affect its energy content?

The empirical formula of a hydrocarbon compound represents the simplest whole number ratio of its elements. Since the energy content is calculated per empirical formula unit, the empirical formula does not directly affect the energy content. However, the type and arrangement of atoms in the compound can affect its energy content.

## 5. Can the energy content of a hydrocarbon compound vary?

Yes, the energy content of a hydrocarbon compound can vary depending on the specific compound and its molecular structure. For example, compounds with longer carbon chains tend to have higher energy content than those with shorter chains. Additionally, the presence of double or triple bonds can also affect the energy content.

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