Efficient Measuring the Enthalpy of Combustion of Hydrocarbon

When it comes to studying the energy content of hydrocarbons, one useful method is measuring their enthalpy of combustion. This can be achieved through a laboratory experiment where a small sample of a hydrocarbon, such as ethanol or hexane, is burned in a calorimeter.

Enthalpy of Combustion

The heat released during the combustion reaction is absorbed by the water in the calorimeter, allowing you to calculate the enthalpy of combustion of the hydrocarbon.

This experiment is meant to determine the amount of energy released by a hydrocarbon when it undergoes complete combustion. By measuring the change in temperature of the water in a calorimeter, the amount of heat absorbed by the water during the combustion reaction can be determined. Using this information, the enthalpy of combustion of the hydrocarbon can be calculated, which provides important information about its energy content and potential as a fuel source.

Materials

Hydrocarbon:  such as ethanol, (C₂H₅OH or hexane (C₆H₁₄), Methane (CH₄), Propane (C₃H₈)

Butane (C₄H₁₀), Pentane (C₅H₁₂), Heptane (C₇H₁₆), Octane (C₈H₁₈), Decane (C₁₀H₂₂), Ethene (C₂H₄), Propene (C₃H₆), and Butene (C₄H₈).

Calorimeter, Thermometer, Stirrer, Distilled Water, Hotplate, Heat-resistant Mat, Balance, Glass Rod

Safety Precautions

1. Wear safety goggles and gloves
2. Use a heat-resistant mat when using the Bunsen burner
3. Handle the hydrocarbon with care as it is flammable
4. Keep the calorimeter away from the edge of the bench to avoid spills
5. Ensure that the calorimeter is stable on the bench

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Procedure

1. Clean and dry the calorimeter and thermometer before use.
2. Weigh the empty calorimeter and record the mass.
3. Add a known mass of distilled water to the calorimeter and measure its initial temperature using the thermometer. Record this value.
4. Add the hydrocarbon to a small copper or stainless-steel container and weigh it.
5. Carefully ignite the hydrocarbon using a match or lighter and allow it to burn completely in the container. Stir the water in the calorimeter continuously during the combustion to ensure even heating.
6. When the combustion is complete, record the final temperature of the water in the calorimeter.
7. Weigh the container with any remaining hydrocarbon and record the mass.
8. Repeat steps 2 to 7 two more times to ensure accurate results.

Calculations

Calculate the mass of the hydrocarbon burned using the difference between the initial and final masses of the container.

Calculate the heat released by the combustion of the hydrocarbon using the equation:

Q = m x c x ΔT

where Q is the heat released, m is the mass of water in the calorimeter, c is the specific heat capacity of water (4.18 J/g °C), and ΔT is the change in temperature of the water.

Calculate the enthalpy of combustion using the equation:

ΔH_comb = -Q/m

where ΔH_comb is the enthalpy of combustion, Q is the heat released, and m is the mass of hydrocarbon burned.

Calculate the average enthalpy of combustion from the three trials.

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Plotting of graph of Enthalpy of Combustion

After obtaining the average enthalpy of combustion of the hydrocarbon, you can plot a graph of the enthalpy of combustion versus the number of carbon atoms in the hydrocarbon molecule.

Make a table of the hydrocarbons used in the experiment and their respective enthalpies of combustion.

Arrange the hydrocarbons in ascending order of their number of carbon atoms.

Plot a graph with the enthalpy of combustion on the y-axis and the number of carbon atoms on the x-axis.

Draw a best-fit line through the data points.

Use the slope of the line to calculate the enthalpy of combustion per carbon atom for the hydrocarbons.

Report the average enthalpy of combustion with uncertainty and state any sources of error or potential improvements to the experiment.

Conclusion

In conclusion, measuring the enthalpy of combustion of hydrocarbons is an important process for determining their energy content. By following the laboratory procedures and guidelines carefully and utilizing the appropriate equipment, such as a calorimeter, accurate and efficient measurements can be obtained. The results of this experiment can provide valuable insights into the combustion efficiency of different hydrocarbons and inform decisions regarding their use as an energy source.