Ice melts at -10°C and 1 atm.
Salt precipitates out of sea water in a sealed bottle.
A piece of paper at room temperature reacts with oxygen to give carbon dioxide and water.
A book absorbs energy from the floor and jumps up back to the shelf.

Which direction (based on spontaneity) would each event occur? The options are Forward, Backward, Both, and None.

Question

Ice melts at -10°C and 1 atm.
Salt precipitates out of sea water in a sealed bottle.
A piece of paper at room temperature reacts with oxygen to give carbon dioxide and water.
A book absorbs energy from the floor and jumps up back to the shelf. 

Which direction (based on spontaneity) would each event occur? The options are Forward, Backward, Both, and None.

jfraser · Answer

a little common sense should be enough to get you to the answers here. Chemists and physicists often say that spontaneity is the "direction" of the universe, that some things just don't happen in certain directions, regardless of the conditions, like temperature, or pressure. Some things can and do happen in reverse, depending on the temperature, usually. Some things will never happen in either direction, forwards or backwards, regardless of how much energy you put in, or how long you wait. An easy way to think of the direction of spontaneity, is to ask yourself "could it happen". In the first case, does ice ever melt at -10C? Certainly not, but the REVERSE often does, so there should be your answer for the first one. The others can all be answered by taking the same point of view.