Summary: Two solids are mixed together in a flask which is then set on a puddle of water on a wood block. The entropically driven endothermic reaction freezes the water, and thus the flask is frozen to the block.
Acid soluble and water soluble salts of barium hydroxide are toxic.
Chemicals and Solutions:
32g Barium Hydroxide octahydrate, solid
16g Ammonium thiocyanate, solid
Small block of wood
Pink litmus paper
Small powder funnel
Small beaker or squeeze bottle of water
It works best to add the barium hydroxide to the ammonium thiocyanate. The ammonium thiocyanate is damp, tending to stick to the inside of the flask, making it more troublesome to transfer.
Ba(OH)2*8H2O(s) + 2NH4SCN(s) ---> Ba(SCN)2 (aq)+ 2NH3(g)+ 10H2O(l)
This reaction is entropically driven.
Because the reaction occurs spontaneously, DG is negative.
Because heat is absorbed by the reaction from the surroundings, DH is positive.
DS is positive because of the formation of ammonia gas and liquid water.The effect of increased entropy more than compensates for the positive enthalpy change.