Determination of enthalpy change of combustion Flashcards Preview

CHEM- component 1 practicals > Determination of enthalpy change of combustion > Flashcards

Flashcards in Determination of enthalpy change of combustion Deck (7)
Loading flashcards...
1

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,

2

2nd step

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

3

3rd step

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

4

4th step

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

5

5th step

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

6

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.

7

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

use of draught screens and input of oxygen gas