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Is the Second Law wrong?
HCl(g) + NH3(g)  NH4Cl(s) |
However, it is not difficult to find examples of chemical reactions that appear to contradict the rule that entropy increases in spontaneous processes. An example is the demonstration where the two gases, hydrogen chloride and ammonia, diffuse along a tube and produce a white ring of solid ammonium chloride:
HCl(g) + NH3(g) NH4Cl(s)
The two gases forming a solid clearly involve a decrease in entropy, yet the reaction occurs spontaneously. In fact we can calculate the numerical value of the entropy change from the figures in Table 3:
Total entropy of starting materials = 187 + 192 = 379 J K -1 mol-1
Entropy of product = 95 J K -1 mol-1
Entropy change = –284 J K -1 mol-1
As expected, a significant decrease. (Remember, we expect spontaneous reactions to have an increase in entropy.) Does this mean the Second Law is wrong?
| Is the Second Law wrong? | |
