Determination of enthalpy change of combustion Flashcards Preview

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Flashcards in Determination of enthalpy change of combustion Deck (7)
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first step for determination of /\HC of methanol?

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,


2nd step

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


3rd step

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


4th step

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


5th step

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


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

-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.


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

use of draught screens and input of oxygen gas