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Combustion of Fossil Fuels

Combustion of Fossil Fuels

Introduction

Use the resources on the Combustion of Fossil Fuels student esheet to answer the questions on this sheet. Be prepared to discuss your answers in class.


Part 1. The Combustion of Fossil Fuels
http://chemistry.elmhurst.edu/vchembook/511natgascombust.html
What do we mean that a hydrocarbon can go through combustion? What are we really doing to the hydrocarbon?

 

 

Why do you think hydrocarbons make good fuels?

 

 

Write the chemical reaction for the combustion of methane.

 

 

How does the combustion of methane compare to the combustion of other hydrocarbon fossil fuels, like coal and oil?

 

 

Part II. Energy of Combustion
http://chemistry.elmhurst.edu/vchembook/512energycombust.html
What is the general chemical formula for the combustion of fossil fuels, or any hydrocarbons?

 

 

Approximately what percentage of the world’s energy needs is fulfilled by the combustion of fossil fuels?

 

 


Combustion produces energy. Where does all this energy come from?

 

 

Based on the diagram for the energy used and produced in the combustion of methane, fill in the chart. Make sure to indicate whether the energy is positive or negative. Also indicate the units.

Step

Description of Combustion Step

Energy Released or Produced

1

How much energy is needed to break all the Carbon – Hydrogen bonds in one methane molecule?

 

2

How much energy is needed to break the Oxygen – Oxygen bonds in two oxygen molecules?

 

3

How much energy is produced to make the Carbon – Oxygen bonds in two carbon dioxide molecules?

 

4

How much energy is produced to make the Hydrogen – Oxygen bonds in two water molecules?

 

What is the total net energy?

 

 

Based on your calculations, is energy needed or produced to combust methane? How do you know this based on your calculation?

 

 

What does the term “endothermic” mean?

 

 

In the steps above, which ones are endothermic?

 

 

What does the term “exothermic” mean?

 

 

In the steps above, which ones are exothermic?

 

 

Overall, is the combustion of methane endothermic or exothermic?

 

 

Part III. Combustion Energy of Ethane
Different hydrocarbons produce different amounts of energy when combusted, or burned. As we know from our calculations, the combustion of methane produces 802 kJ of energy. How much energy is produced from the combustion of ethane? Use the bond energy chart found on the top of the online resource, Energy from Fossil Fuels: (http://www.wou.edu/las/physci/GS361/Energy_From_Fossil_Fuels.htm.

 

 

What is the correct chemical reaction for the combustion of ethane?

 

 

Determine the bond energies in each step of the combustion of ethane. Two steps are provided for you as examples.

Step 1:

Breaking of C-H bonds in ethane

Bond energy of one C-H bond

Number of bonds in one molecule

Total energy needed for one molecule

Number of molecules

Total energy needed for all molecules

410 kJ/mole

6

2460 kJ/mole

2

+4920 kJ/mole

 

Step 2:

Breaking of C-C bonds in ethane

Bond energy of one C-C bond

Number of bonds in one molecule

Total energy needed for one molecule

Number of molecules

Total energy needed for all molecules

 

 

 

 

 

 

 

Step 3:

Breaking of O-O bonds in oxygen

Bond energy of one O-O bond

Number of bonds in one molecule

Total energy needed for one molecule

Number of molecules

Total energy needed for all molecules

 

 

 

 

 

 

 

Step 4:

Making of C-O bonds in carbon dioxide

Bond energy of one C-O bond

Number of bonds in one molecule

Total energy needed for one molecule

Number of molecules

Total energy produced for all molecules

799 kJ/mole

2

1598 kJ/mole

4

- 6392 kJ/mole

 

Step 5:

Making of O-H bonds in water

Bond energy of one O-H bond

Number of bonds in one molecule

Total energy needed for one molecule

Number of molecules

Total energy produced for all molecules

 

 

 

 

 

 

 

 

What is the total combustion energy for ethane?

 

 

 Is energy needed for this reaction or is it produced?

 

 

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