Over my last couple of posts I’ve defined reaction and equilibrium. I’ve also explained why a reaction will proceed spontaneously. (For background see here<\/a> and here<\/a>.)<\/p>\n Today, the focus is equilibrium: why a given chemical system may not decisively transform in one direction, but instead persist in two complementary forms. Consider, by example, the following equilibrium:<\/p>\n 3H2<\/sub>+N2<\/sub> \u21cb 2NH3<\/sub>, \u0394H=-92kJ\/mol<\/p>\n Recall, from my previous post<\/a>, Nature’s two preferred trends:<\/p>\n High entropy favours the left side of the equilibrium above, since it has 4 molecules, as opposed to only 2 on the right. However, low enthalpy favours the right side, denoted by negative \u0394H.<\/p>\n With one of Nature’s trends driving to the left, while the other is driving to the right, the system remains undecided; the molecules constantly break down and reform from side to side. Left alone, a stable proportion of each will persist, while the individual molecules constantly change between forms. Such is an equilibrium.<\/p>\n Source:<\/p>\n Hebden, James A. Chemistry: Theory and Problems<\/u>, book 2. Toronto: McGraw-Hill Ryerson, 1980.<\/p>\n Mortimer, Charles E. Chemistry<\/u>, 6th ed. Belmont: Wadsworth, 1986.<\/p>\n\n