Heats of Combustions



Heats of Combustions

Practice Problems

1) a. How much energy (in kJ) is released by burning 25.0 mol of hexane?

b. How much energy is released by burning 25.0 g of hexane?

2) 2 C2H2 + 5 O2 ( 4 CO2 + 2 H2O + 2512 kJ

a. What is the molar heat of combustion of acetylene (C2H2) in kilojoules per mole?

b. If 12 mol of acetylene burns fully, how much thermal energy will be produced?

3) Write a balanced equation that includes thermal heat for these alkanes:

a. propane

b. butane

4) a. How much thermal energy is produced by burning two moles of octane?

b. How much thermal energy is produced by burning one gallon (2660 g) of octane?

c. Suppose a car operates so inefficiently that only 16% of thermal energy from burning fuel is converted to useful “tire-turning” (mechanical) energy. How many kilojoules of useful energy would be stored in a 20.0-gallon tank of gasoline (octane)?

Heats of Combustions

Practice Problems

1) a. How much energy (in kJ) is released by burning 25.0 mol of hexane?

c. How much energy is released by burning 25.0 g of hexane?

2) 2 C2H2 + 5 O2 ( 4 CO2 + 2 H2O + 2512 kJ

a. What is the molar heat of combustion of acetylene (C2H2) in kilojoules per mole?

c. If 12 mol of acetylene burns fully, how much thermal energy will be produced?

3) Write a balanced equation that includes thermal heat for these alkanes:

c. propane

d. butane

4) a. How much thermal energy is produced by burning two moles of octane?

d. How much thermal energy is produced by burning one gallon (2660 g) of octane?

e. Suppose a car operates so inefficiently that only 16% of thermal energy from burning fuel is converted to useful “tire-turning” (mechanical) energy. How many kilojoules of useful energy would be stored in a 20.0-gallon tank of gasoline (octane)?

|Heats of Combustion For Selected Hydrocarbons |

|Hydrocarbon |Formula |Heat of Combustion (kJ/g) |Molar Heat of Combustion (kJ/mol) |

|Methane |CH4 |55.6 |890 |

|Ethane |C2H6 |52.0 |1560 |

|Propane |C3H8 |50.0 |2200 |

|Butane |C4H10 |49.3 |2859 |

|Pentane |C5H12 |48.8 |3510 |

|Hexane |C6H14 |48.2 |4141 |

|Heptane |C7H16 |48.2 |4817 |

|Octane |C8H18 |47.8 |5450 |

|Heats of Combustion For Selected Hydrocarbons |

|Hydrocarbon |Formula |Heat of Combustion (kJ/g) |Molar Heat of Combustion (kJ/mol) |

|Methane |CH4 |55.6 |890 |

|Ethane |C2H6 |52.0 |1560 |

|Propane |C3H8 |50.0 |2200 |

|Butane |C4H10 |49.3 |2859 |

|Pentane |C5H12 |48.8 |3510 |

|Hexane |C6H14 |48.2 |4141 |

|Heptane |C7H16 |48.2 |4817 |

|Octane |C8H18 |47.8 |5450 |

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