Parr Instrument 6755 - Manual (Page 27)

Calculations
6755 5
w w w . p a r r i n s t . c o m 25
Figure 4
Endothermic Reaction
Example - Endothermic Reaction
Problem: Determine the heat of solution of solid
potassium nitrate, KNO
3,
when dissolved in
water.
KNO
3
m = 0.7180 gram
Distilled water = 100.00 grams
Corrected temperature rise
∆T
C
= -0.508 °C (from Figure 3)
T(0.63R) = 25.400 °C
Energy equivalent
e = 121.46 cal/°C
Energy evolved
Q = (∆T
C
) (e)
= (-0.508) (121.46)
= -61.70 calories
Enthalpy change
=
=
= -34.99 cal/g @ 24.885 °C
Or, multiplying by the molecular weight of KNO3
= (85.94) (101.10)
= 8.69 Kcal/mole @ 25.400 °C
0.7180g solid KNO
3
dissolved in
100.00g of distilled water
Temperature at
time of mixing
25.714 °C
R = ∆T
C
-0.508 °C
0.63R -0.320 °C
T
i
25.720 °C
T(0.63R) = T
i
+ 0.63R 25.400 °C
T
f
= T
i
+ R 25.212 °C