Determination of enthalpy change of combustion Flashcards

(7 cards)

1
Q

first step for determination of /\HC of methanol?

A

1) using a measuring cyliner, measure out 150 cm^3 of water, pour water into beaker, record initial temp. of water to the NEAREST 0.5 degrees c,

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2
Q

2nd step

A

2) add methanol to spirit burner, weigh spirit burner containing the methanol

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3
Q

3rd step

A

3) place spirit burner under the beaker with clamp holding beaker and thermometer in beaker.

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4
Q

4th step

A

4) after 3 mins extinguish flame and immediately record max. temp reached by the water

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5
Q

5th step

A

5) re-weigh the spirit burner containing methanol and assume that the wick has not been burnt

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6
Q

how may the experimental enthalpy change of combustion value be inaccurate?

A
  • heat loss to surroundings other than water, (includes beaker but mainly air surrounding)
  • incomplete comb. of methanol (CO and C being produced instead of CO2)
  • evaporation of methanol from the wick (therefore burner should be weighed as soon as possible after extinguishing the flame spirit burners usually hve a cover to reduce error)
  • non-standard conditions.
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7
Q

what can be used to minimise errors from heat loss and incomplete combustion ?

A

use of draught screens and input of oxygen gas

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