A Vigorous, Spontaneous Endothermic Reaction Submitted by: Malcolm D. Hawkins, Chemistry Department, Mander College, Bedford, England, Checked by: William Dodd, Hiram College, Hiram, Ohio 44234 PREPARATION
REMARKS
DEMONSTRATION
The temperature drop for this endothermic reaction can entropy increase due to the to a he large volume increase associated with the formation of gaseous products:
(CAUTION: USE FUME HOOD.) Add the 15 g of CoS04.7H20 to the SOCh and stir. The pink solution turns to purple in a minute or two and the vigorous reaction is underway. The temperature drops 20"C, or more.
Other salts, such as Crz(S04)a.15H20, or alum, may also he used. The low temperature is reached in 5-10 min hut the reaction continues for 30 min or more, maintaining the temperature near the minimum value.
Provide 40 ml of thionyl chloride (SOCIz), 15 g CoSO4. 7Hz0, 100-ml beaker, thermometer or thermocouple.
A178
/ Journal of Chemical Education
CoS0,.7H20
+ 7SOC12
-
CoSO,
+ ISO, + 14HCI
