4. how long does a hydrogen bond last? 5. how does the constant bonding and breaking apart of water…

Brief Explanations:

Hydrogen bonds in water are transient. They typically last for a very short - time, on the order of picoseconds (10^-12 seconds). The constant formation and breaking of hydrogen bonds between water molecules contribute to cohesion because even though individual bonds are short - lived, there are always many hydrogen bonds present at any given moment, which hold the water molecules together.

Answer:

4. Hydrogen bonds in water last on the order of picoseconds (10^-12 seconds).
5. The constant bonding and breaking of water molecules contribute to cohesion as there are always many hydrogen bonds present at any given time, holding the water molecules together.