A chlorine Cl and bromine Br atom are adsorbed on a small patch of surface (see sketch at right). This patch is known to contain 81 possible adsorption sites. The Cl and bromine Br atoms have enough energy to move from site to site, so they could be on any two of them. Suppose the Br atom desorbs from the surface and drifts away. Calculate the change in entropy. Round your answer to 2 significant digits, and be sure it has the correct unit symbol.

)benzene and toluene form nearly ideal solutions. consider an equimolar solution of benzene and toluene. at 20 °c the vapour pressures of pure benzene and toluene are 9.9 kpa and 2.9 kpa, respectively. the solution is boiled by reducing the external pressure below the vapour pressure. calculate (i) the pressure when boiling begins, (ii) the composition of each component in the vapour, and (iii) the vapour pressure when only a few drops of liquid remain. assume that the rate of vaporization is low enough for the temperature to remain constant at 20 °c.