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    1) 200 cm^3 of 1.0M copper (II) sulphate solution were placed in an expanded polystyrene cup. When the solution had reached a steady temperature of 18.5 degrees C, 7g of powdered iron were added and the mixture was stirred rapidly. The highest temperature reached was 41.5 degrees C.

    a) Calculate the enthalpy change for this reaction. (The specific heat capacity of water is 4.18 J g^ -1 K^ -1) - (200g x 4.18 x 23 = 19228)
    b) State 3 assumptions which are made in this calculation. - ?

    2) In an experiment to determine the enthalpy of combustion of ethanol, a small spirit lamp containing ethanol was lit and the energy released was used to heat up a known mass of water in a copper calorimeter. The results from the experiment were:
    Mass of calorimeter empty = 150g
    Mass of calorimeter + water = 250g
    Initial mass of spirit lamp and ethanol = 78.45g
    Final mass of spirit lamp and ethanol = 77.56g
    Initial temperature of water in calorimeter = 23 degrees C
    Final temperature of water in calorimeter = 88 degrees C
    The specific heat capacity of water = 4.18 J g^ -1 K ^ -1
    The specific heat capacity of the material of the calorimeter = 0.42 J g^ -1 K^ -1
    From these results calculate the enthalpy of combustion of ethanol as follows:

    a) Mass of ethanol burned - (78.45g - 77.56g = 0.89g)
    b) Moles of ethanol burned - (0.89/46 = 0.02 mol)
    c) Temperature rise of the water and calorimeter - (88 - 23 = 65)
    d) Energy gained by the water - ?
    e) Energy gained by the calorimeter - ?
    f) Total energy gained = energy released by the ethanol - ?
    g) Energy released by burning 1 mole of ethanol - ?

    I have answered some in brackets which I am pretty sure are right, so if anybody could confirm it would be great, also those I haven't answered I left with a "?", so could anybody explain how to do those ones? Many thanks
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    (Original post by adil12)
    1) 200 cm^3 of 1.0M copper (II) sulphate solution were placed in an expanded polystyrene cup. When the solution had reached a steady temperature of 18.5 degrees C, 7g of powdered iron were added and the mixture was stirred rapidly. The highest temperature reached was 41.5 degrees C.

    a) Calculate the enthalpy change for this reaction. (The specific heat capacity of water is 4.18 J g^ -1 K^ -1) - (200g x 4.18 x 23 = 19228)
    b) State 3 assumptions which are made in this calculation. - ?
    There is no heat lost to the surroundings
    The solution has a density = 1g/cm3
    The shc of copper sulphate solution is the same as that of water
    The polystyrene cup absorbed no heat, nor did the thermometer.


    (Original post by adil12)
    2) In an experiment to determine the enthalpy of combustion of ethanol, a small spirit lamp containing ethanol was lit and the energy released was used to heat up a known mass of water in a copper calorimeter. The results from the experiment were:
    Mass of calorimeter empty = 150g
    Mass of calorimeter + water = 250g
    Initial mass of spirit lamp and ethanol = 78.45g
    Final mass of spirit lamp and ethanol = 77.56g
    Initial temperature of water in calorimeter = 23 degrees C
    Final temperature of water in calorimeter = 88 degrees C
    The specific heat capacity of water = 4.18 J g^ -1 K ^ -1
    The specific heat capacity of the material of the calorimeter = 0.42 J g^ -1 K^ -1
    From these results calculate the enthalpy of combustion of ethanol as follows:

    a) Mass of ethanol burned - (78.45g - 77.56g = 0.89g)
    b) Moles of ethanol burned - (0.89/46 = 0.02 mol)
    c) Temperature rise of the water and calorimeter - (88 - 23 = 65)
    d) Energy gained by the water - ?
    e) Energy gained by the calorimeter - ?
    f) Total energy gained = energy released by the ethanol - ?
    g) Energy released by burning 1 mole of ethanol - ?

    I have answered some in brackets which I am pretty sure are right, so if anybody could confirm it would be great, also those I haven't answered I left with a "?", so could anybody explain how to do those ones? Many thanks
    d) you have already used the formula in the first question ΔH = mcΔT

    just apply it to the mass of water in the calorimeter

    e) d) you have already used the formula in the first question ΔH = mcΔT

    just apply it to the mass of the calorimeter

    f) add up d & e above

    g) factor the answer to be per mole of ethanol
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    (Original post by charco)
    There is no heat lost to the surroundings
    The solution has a density = 1g/cm3
    The shc of copper sulphate solution is the same as that of water
    The polystyrene cup absorbed no heat, nor did the thermometer.




    d) you have already used the formula in the first question ΔH = mcΔT

    just apply it to the mass of water in the calorimeter

    e) d) you have already used the formula in the first question ΔH = mcΔT

    just apply it to the mass of the calorimeter

    f) add up d & e above

    g) factor the answer to be per mole of ethanol
    Regarding question 2, you would take the mass of water as 100g? And for part e) the mass of the calorimeter as 150g?
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    (Original post by adil12)
    Regarding question 2, you would take the mass of water as 100g? And for part e) the mass of the calorimeter as 150g?
    that's what the question tells you...

    ... why would you want to use different values? :confused:
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    (Original post by charco)
    that's what the question tells you...

    ... why would you want to use different values? :confused:
    I was just wondering if you would have to use their combined mass for any of them that's all :rolleyes:
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    (Original post by charco)
    that's what the question tells you...

    ... why would you want to use different values? :confused:
    What value of delta T would You use for letter e) ?
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    (Original post by adil12)
    What value of delta T would You use for letter e) ?
    The temperature change has to be the same for both the calorimeter and the water it contains...
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    One further assumption in the Cu question- the rapid stirring does not lead to a significant temperature rise
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    (Original post by Cora Lindsay)
    One further assumption in the Cu question- the rapid stirring does not lead to a significant temperature rise

    There are quite a few others:

    the excess zinc does not absorb energy (of course it does)
    the copper formed does not absorb energy (ditto)
    there is no evaporation
 
 
 
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