Thursday, February 10, 2011

Wednesday, February 9, 2011

Heat of Hydration

for aqueous ionic solutions,
• Solvent attractive forces and Mixing forces are
combined into a term called the heat of hydration
∆Hsolvent + ∆Hmix = ∆hhydration
 attractive forces in water = H-bonds
 attractive forces between ion and water = ion-dipole
 ∆Hhydration = heat released when 1 mole of gaseous ions
dissolves in water
 ∆Hsolute = - ∆Hlatic

Heat of Hydration
The term ‘heat of hydration’ is applied to the heat generated by the chemical reactions, which occur in setting concrete between the water and cement. The heat causes the concrete first to expand and then to shrink as it cools. If there is a temperature gradient across the concrete or the concrete is otherwise restrained, cracking may occur. The two factors, which are most likely to cause excessive generation of heat, are very large pours and high cement contents. Some specifications set a maximum cement content in order to limit the generation of heat.

Thursday, February 3, 2011

Tuesday, February 1, 2011

Super Steam Heat can burn paper

Decomposition of Hydrogen Peroxide

This is a set up for Decomposition of Hydrogen Peroxide. H2O2. The yellow hexagon shape you see is an inverted graduated cylinder. It is filled with water. You may have played with a similar set up as a kid in a bath tub. If you invert a container in water, it does not lose any water in the cylinder. A syringe is filled with 3 ml of KI (Potassium Iodine. The tube is then inserted into the cylinder. The Erlenmeyer flask has a rubber stopper so it is air tight. One the syringe is injected into the flask that is filled with air, the reaction cause a release of gas which then travels through the tube and into the graduated cylinder. The gas displaces the water from the cylinder into the container.