Hydrocarbons are among the most common fuels that are commercially available. In this class, you have learned that energy can be harvested from hydrocarbons when they undergo combustion, i.e., reaction with oxygen. One aspect of combustion often neglected is the fact that not every combustion is complete, meaning the hydrocarbon reactant is not completely converted to carbon dioxide and water. In fact, even the most perfectly regulated combustion reactions, such as the ones carried out with special burners, are commonly incomplete to at least some degree. See sections 1.2-3 and 7.5 of the eText.
This begs the following questions:
- What makes a combustion reaction complete?
- If the combustion is not complete, are there various degrees of incomplete combustion?
The answer to the first question comes straight from the class materials, and complete combustion happens when the only products of the combustion are CO2 and H2O gases. When the combustion is incomplete, two other possible products are made: (C(s)) and carbon monoxide gas (CO(g)).
Claim Your Hydrocarbon
Step 1: To begin the project, go to the Module 4 Claim Your Hydrocarbon! discussion in D2L to claim your hydrocarbon, which will take the form, CxH2x+2 (Example: If the hydrocarbon you pick has 14 carbon atoms, the number of hydrogens for it will be (14×2)+2 = 30. Thus, the formula of your hydrocarbon would be C14H30)
Step 2: Since part of the project deals with incomplete combustion, and there are virtually infinite degrees of incomplete combustion, you will also have to download the spreadsheet that provides the moles of products, provide the number of moles of carbon in one mole of your fuel, and the spreadsheet will give you the number of moles of the products C(s), CO(g) and CO2(g) that you will be using in the project, as well as the temperature of the flame for this combination of products.
Step 3: With the number of moles of carbon products provided by the spreadsheet and keeping in mind that you are combusting only one mole of your fuel, you can balance the rest of the equation. Here is an example of one such equation, at room temperature, after balancing:
C16H34(s) + 19.21 O2 –> 3.38 C(s) + 3.82 CO(g) + 8.80 CO2(g) +17H2O(l)
Step 4: Notice that there is one mole of fuel, and the balancing coefficients in italics and underlined, came from the spreadsheet. You must determine the other two balancing coefficients that are in bold.
Research and Respond
Your project will consist of your answers to the following questions. Show all your work using typed answers. Handwritten answers will receive no credit!
- Research the state of your fuel at room temperature (RT, 25oC)
- Write down the balanced equation for the complete combustion of one mole of your fuel, assume RT to determine the states of the substances in the equation. Fractions for stoichiometric coefficients are acceptable and necessary. Remember that the only products of the combustion are CO2 and H2O gas.
- Write down the balanced equation for the assigned incomplete combustion of one mole of your fuel, assume RT to determine the states of the substances in the equation. You must use the coefficients for the products that you got from the spreadsheet!
- Determine the standard enthalpy of combustion of the reactions from questions 2 and 3, using the broken vs. formed bonds method explained in section 9.4 of your textbook. Include a table of bonds broken and formed like Module 4 Discussion 1. Be very detailed in your work, listing the bond enthalpies used in the calculation. For example
Type the balanced Equation for Complete Combustion, then show the table. Repeat for incomplete combustion analysis.
|Broken Bonds Type
|Number Bond Type
|Formed Bond Type
|Number Bond Type
See Example 9.16 for how to show your work.
- Using the answers from question #4, explain which reaction would produce a hotter flame after burning one mol of the fuel under standard conditions. Explain your answer in light of the answers to question #4.
- What physical observations would help you to differentiate complete from incomplete combustion? Give at least two such observations.
- Assuming that the temperature of the flame for complete combustion of your fuel is 2,500. oF, and that the atmospheric pressure is 1.000 atm, calculate the volume of the gaseous reactants, the gaseous products, and the volume change (volume of products – volume of reactants) for the reaction in question #2. Important: Don’t forget that states are temperature and pressure dependent, and the reactants and the products are at 2,500. oF and 1.000 atm.
- With the temperature of the flame for your incomplete combustion that you obtained from the spreadsheet, and knowing that the atmospheric pressure is 1.000 atm, calculate the volume of the gaseous reactants, the gaseous products, and the volume change (volume of products – volume of reactants), for the reaction in question #3. Comment on the differences in change in volume between reactants and products for complete vs incomplete combustion. Important: Don’t forget that states are temperature and pressure dependent, and the reactants and the products are at the temperature you got from the spreadsheet and a pressure of 1.000 atm.
- If the gaseous products from questions 7, and 8, are allowed to cool to a temperature of 250.0 oF, what would the volume of gaseous products be in each case? Explain the difference in volume after this temperature change.
- Furnaces must be inspected and tuned up yearly. Research how this is related to incomplete combustion and briefly discuss the possible consequences of not checking furnaces for the well-being of people and animals.
These questions are about additional gas properties and will be found on D2L quiz called Module 4 Project Extension Questions.
- Go to the quiz titled Module 4 Project Extension Questions.
- The quiz will supply you with randomly generated question values. Use these values in your calculations. The quiz is not graded but submitting your answer will confirm your calculations are correct. Submit the quiz so your instructor can see the submission.
- Copy the question or add a screen shot to your project document.
- If your answers for the quiz were incorrect, you are allowed to re-work the problems to get the correct answers you will see after you take the quiz.
- Include your calculations to submit with this project. For each question, indicate the values used, show all your work clearly using an equation editor in the word processor.
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