# Enthalpy of Combustion

1. When a substance was burned, it raised the temperature of 200 cm3 of water from 21 oC to 25.5 oC. What quantity of heat that was released by this reaction?

2. A Bunsen Burner is used to heat 0.5 kg of water from 20.5 oC to 39.5 oC. How much heat energy has been produced?

3. An alcohol is burned to heat up 100 cm3 of water from 10 oC to 18 oC. How much heat energy has been released?

4. If 0.1 moles of a substance burns to produce enough heat to raise the temperature of 500 cm3 of water from 25 oC to 50oC, calculate the enthalpy of combustion of this substance.

5. 0.05 moles of a fuel was burned and it raised the temperature of 100 cm3 of water from 18.2 oC to 24.5 oC. What is the enthalpy of combustion of this fuel?

6. When 1g of ethanol (C2H5OH) was burned, the heat produced warmed 5 litres of water from 18oC to 18.5oC. What is the enthalpy of combustion of ethanol?

7. When 1g of Sulphur was burned, the heat produced warmed 110g of water from 180C to 18.5oC. What is the enthalpy of combustion of Sulphur?

8. 0.32g of methanol (CH3OH) was burned and it heated up 200 cm3 of water from 19.5 oC to 27.5 oC. Calculate the enthalpy of combustion of methanol.

9. 0.2g of methane (CH4) was burned and it heated up 250 cm3 of water from 18.5 oC to 28.5 oC. Calculate the enthalpy of combustion of methane.

10. 0.22g of propane (C3H8) was burned and it heated up 150 cm3 of water from 21 oC to 31 oC. Calculate the enthalpy of combustion of propane.

11. Butane (C4H10) is used to heat 175 cm3 of water from 22.2 oC to 31.7 oC. What is the enthalpy of combustion of butane if 3g of the gas had been used?

12. Ethanol, C2H5OH, can be used as a fuel in some camping stoves.

The enthalpy of combustion of ethanol is −1367 kJ mol−1.  Using this value, calculate the number of moles of ethanol required to raise the temperature of 500 g of water from 18 °C to 100 °C.

13.      A value for the enthalpy of combustion of butan-2-ol, C4H9OH, can be determined experimentally using the apparatus shown.

Mass of butan-2-ol burned = 1·0 g

Temperature rise of water = 40 °C

Use these results to calculate the enthalpy of combustion of butan-2-ol, in kJ mol–1.

14.      Diborane can be used to manufacture pentaborane (B5H9).

Pentaborane was also considered for use as a rocket fuel because its enthalpy of combustion is − 9037 kJ mol−1.

Calculate the energy released, in kJ, when 1 kilogram of pentaborane is completely burned.

15.      A pupil found the enthalpy of combustion of propan-1-ol using the following apparatus.

(a) In addition to the initial and final temperatures of the water, what other measurements would the pupil have made.

(b) Describe a change that could be made to the experimental procedure in order to achieve more accurate results.

(c) The table shows the enthalpies of combustion of three alcohols.

 Alcohol Enthalpy of combustion/kJ mol-1 methanol -715 ethanol -1371 propan-1-ol -2010

Why is there a regular increase in enthalpies of combustion from methanol to ethanol to propan-1-ol?

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