Parr-instrument 6755 Bedienungsanleitung PDF herunterladen (Seite 26)

Calculations

Parr Instrument Company

Figure 3

Exothermic Reaction

Example - Exothermic Reaction

Problem: Determine the change in enthalpy for

solid sodium sulfate, Na

, when dissolved in

a 5 gram/liter aqueous solution of barium chlo-

ride, BaCl

• 2H

0.1458 grams

solution

100.00 grams

Corrected temperature rise

∆T

= 0.042 °C (from Figure 3)

T(0.63R) = 24.885 °C

Energy equivalent

e = 121.46 cal/°C

Energy evolved

Q = (∆T

) (e)

= (0.042) (121.46)

= 5.1013 calories

Enthalpy change

= -34.99 cal/g @ 24.885 °C

Or, multiplying by 142.04 (the molecular weight

of Na

)

= (-34.99) (142.04)

= -4.970 Kcal/mole @ 24.885 °C

0.1458 g solid Na

dissolved in

100.00 g of 5 g/l aqueous

BaCl

• 2H

Temperature at

time of mixing

24.852 °C

R = ∆T

0.042 °C

0.63R 0.026 °C

24.859 °C

T(0.63R) = T

+ 0.63R 24.885 °C

= T

+ R 24.901 °C

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