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Chemistry Past Paper - Puzzled :3 watch

1. Can anyone give me a hand which this: I've worked it out but I keep getting – 668.8 kJmol-1 . I know this isn't the right answer but I can't work it out??

Process 3 Complete combustion of ethanol:
CH3CH2OH + 3O2 ---> 2CO2 + 3H2O

A student carried out a simple laboratory experiment to measure the enthalpy change for Process 3. The student showed that the temperature of 200 g of water increased by 8.0°C when 0.46 g of pure ethanol was burned in air and the heat produced was used to warm the water.

Use these results to calculate the value, in kJ mol–1, obtained by the student for this enthalpy change. (The specific heat capacity of water is 4.18 JK–1 g–1)

Thank you Chemistry Lovelies!
2. The enthalpy change is (4.18JK-1g-1 * 200g * 8K) = -6688J. The number of moles in 0.46g of ethanol is 0.46/46 = 0.01 mol. So the enthalpy change is -6688J/0.01mol = -668.8kJmol-1. I think you're right.

The standard enthalpy of combustion for ethanol is -1370.7kJmol-1 and since a lot of heat would be lost in such an experiment, an answer of -668.8kJmol-1 sounds reasonable.
3. (Original post by ghjohn)
Can anyone give me a hand which this: I've worked it out but I keep getting – 668.8 kJmol-1 . I know this isn't the right answer but I can't work it out??

Process 3 Complete combustion of ethanol:
CH3CH2OH + 3O2 ---> 2CO2 + 3H2O

A student carried out a simple laboratory experiment to measure the enthalpy change for Process 3. The student showed that the temperature of 200 g of water increased by 8.0°C when 0.46 g of pure ethanol was burned in air and the heat produced was used to warm the water.

Use these results to calculate the value, in kJ mol–1, obtained by the student for this enthalpy change. (The specific heat capacity of water is 4.18 JK–1 g–1)

Thank you Chemistry Lovelies!
Yup, as the chlorine lover says "you are right!"
4. Thanks guys - I must be better at Chemistry than I thought! Knew you guys would help!
5. Thanks guys - I must be better at Chemistry than I thought! Knew you guys would help!
6. (Original post by ghjohn)
Thanks guys - I must be better at Chemistry than I thought! Knew you guys would help!
... you can say that again!

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