As an introduction to this chapter we will look at two chemical reactions which clearly demonstrate the important characteristics we are going to discuss. The first reaction is between aluminum (Al) and iron (III) oxide (Fe2O3).The reaction is;2Al(s) + Fe2O3(s) ----> Al2O3(s) + 2Fe(s)The two reactants are mixed together and the reaction is initiated by adding a few drops of concentrated sulfuric acid to a another mixtrue of potassium clorate and sugar that has been placed on top of the Al/Fe2O3 mixture.(Click on the picture on the right to view the reaction.) |
The second reaction is between barium hydroxide and ammonium chloride. Both of these reactants are white crystalline solids. The two white solids are mixed together in a erlenmeyer flask. Before the reaction begins the two solids are at room temperature as is the flask. When the two solids are mixed the first observation is the two solids form a slurry, as a liquid is formed. This is very interesting, but not surprising when you are told water is a product of the reaction. The second observation occurs when the flask is picked up. The temperature has fallen when the two reactants are mixed to a very low temperature. The reaction is;Ba(OH)2.8H2O(s) + 2NH4SCN(s) ---> Ba(SCN)2(aq) + 2NH3(g) + 10H2O(l)As the two white solids are mixed we observed how the temperature of the reaction changed. The temperature is falling-it is getting cooler. Notice also the change which has occurred in the flask. The two solids have changed and we now have a liquid. If we could smell the reaction vessel it would smell of ammonia. Heat is a reactant, it is absorbed by the reactants.(Click on the picture on the right to view the reaction.) |
Specific Heat of H2O(s) |
2.09 J g-1 C-1 |
Specific Heat of H2O(l) |
4.184 J g-1 C-1 |
Specific Heat of H2O(g) |
1.84 J g-1 C-1 |
Enthalpy of fusion |
6.01 kJ mol-1 |
Enthalpy of vaporization |
40.67 kJ mol-1 |
Substance |
Specific HeatJ g-1 C-1 |
Aluminum |
0.901 J g-1 C-1 |
Carbon(graphite) |
1.84 J g-1 C-1 |
Copper |
0.3844 J g-1 C-1 |
water |
4.18 J g-1 C-1 |
Iron |
0.449J g-1 C-1 |
Mercury |
0.1395 J g-1 C-1 |
Oxygen |
0.9172J g-1 C-1 |
Nitrogen |
1.040J g-1 C-1 |