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Flip-flopping of lipids (and in proteins it is impossible) in plasma membrane is rare due to high energy barrier (video ref). However, it is an important mechanism since it allows asymmetric distribution of lipids in cell membrane. Question: If a specific lipid is flipped E.g. phosphatidylinositol from cytoplasm side to extra-cellular side (E.g. by flippase), what mechanism can the cell do to ensure it will stay towards the extra-cellular fluid side but not flip-flop AGAIN (i.e. establish the asymmetry & enable its function)?

I encountered catalytic hydrogenation recation, where alkene is converted into alkane using Pt/C or Pd/C as catalyst, but I have a question: Bond dissociation energy of H2 = 436kJ/mol. But when H2 is adsorbed on the metal surface, the bond is broken. How come this simple step can break this strong bond? Where does the 436kJ energy come from / what gives this activation energy?

According to my knowledge, negative deviation of the Law is because: - solute-solvent intermolecular attraction is larger in magnitude than both solute-solute & solvent-solvent interactions, so solution reaction is exothermic. With very strong interactions, molecules become less able to escape from the liquid surface and form vapor, hence a lower vapor pressure than Raoult's Law prediction. My question: In terms of intermolecular adhesive force(PE), the above explanation is true. However, the reaction is exothermic (since dH(soln) is negative usually), meaning heat is given out. This increased temperature of the solution hence the KE of molecules. According to the Maxwell-Boltzmann distribution, a higher % of liquid molecules can escape from the liquid surface can into vapor phase. Won't this increase the vapor pressure of the solution instead of a negative deviation? Vice versa, for endothermic dissolution reaction, positive deviation of the Law occurs, but the temperature of the solution drops, won't this pull down the vapor pressure of solution? Thanks a lot in advance and please correct me if I have made any mistakes!