Study Guide 3.8.cwk

Name Study Guide 3.8Period C.6, Your Turn 3.7, C.7C.6 Using Heats of Combustion (p. 201)Using Heats Of Combustion, Altering Fuels1. Where does the heat usually show up in a combustion reaction?2. What are the units for heat of combustion?3. Set up a mathematical expression and calculate kJ/g for C 2 H 6 .Your Turn 3.7: Heats of Combustion (p. 202)4. 1. How much energy (in kilojoules) is released by completely burning 25.0 mol of hexane?2. Write a chemical equation , including thermal energy, for the complete combustion of:a. methaneb. butane3. Examine the data summarized in Table 5.a. How does the trend in heats of combustion for hydrocarbons expressed in kJ/g comparewith that expressed in kJ/mol?b. Assuming the trend continues to large hydrocarbons, predict the heat of combustion fordecane in units of kJ/g and kJ/mol.kJ/g kJ/molc. Which prediction in question 3b was easier? Why?4. a. How much thermal energy is produced by burning two moles of octane?

4. b. How much thermal energy is produced by burning one gallon (2660 g) of octane?c. Suppose your car operates so inefficiently that only 16% of the thermal energy fromburning fuel is converted to useful mechanical energy. How many kilojoules of usefulenergy would be stored in a 20.0 gallon tank of gasoline?5. The heat of combustion of carbon as coal is 294 kJ per mole.a. Write a chemical equation for burning carbon. Include the quantity of thermal energy.b. Gram for gram, which is the better fuel - carbon or coal? Explain.c. In what applications might carbon as coal replace petroleum based fuel?d. Describe one application in which coal would be a poor substitute for petroleum.C.7 Altering Fuels (p. 204)5. How does modern cracking of petroleum differ from the World War I process?6. Write an equation for cracking C 12 H 26 (dodecane)7. Why do some gasolines “knock”?700ºCC 12 H 26 (g) > +8. An additive such as tetraethyl lead slows down the reaction period.a. What changes does this additive make in the octane number?b. Why is this additive being used less and less?9. What is meant by a branched chain molecule?