Chapter 8 Those incredible water molecules Water is the most important substance on earth and in any living organism. Why
Chapter 8 Those incredible water molecules Water is the most important substance on earth and in any living organism. Why?
8. I Water molecules form an open crystalline structure in ice When water freezes the water molecules arrange themselves in a Six-sided crystalline structure Increased structural orderliness usually means increased density Solids and crystals have high structural orderliness and are thus denser than liquid and non-crystalline materials. But water is exception (dense) dless dense later molecules in the liquid phase are arranged more compactly than water molecules in the solid phase, where they form an open crystalline structure
8.1 Water molecules form an open crystalline structure in ice When water freezes, the water molecules arrange themselves in a six-sided crystalline structure. Increased structural orderliness usually means increased density. Solids and crystals have high structural orderliness and are thus denser than liquid and non-crystalline materials. But water is exception
8.2 Freezing and melting go on at the same time Hydrogen bonds form during freezing of water, releasing heat They break during melting, absorbing heat Adding salt to water decreases the melting point of water Aqueous solution of Nacl Fiqure 8.9 (a)In a mixture of ice and liquid water at oC, the number of H2O molecules entering the solid phase is equal to the number of H2o molecules entering the liquid phase. (b) Adding a solute such as sodium chloride, decreases the number of H2O molecules entering the solid phase because now there are fewer liquid H2o molecules at the interface
8.2 Freezing and melting go on at the same time Hydrogen bonds form during freezing of water, releasing heat. They break during melting, absorbing heat. Adding salt to water decreases the melting point of water
Water is densest at4℃ When the temperature of Liquid water a given is increased its molecules vibrate Temperature(C) faster and move 10014 farther apart. So the substance expands 10008 This is the case in all 1000 three phases of water apart from the liquid water from 0-4C. The reason IS“ice-like UPon warming. the crystals collaps crystal structure starts Above 4 C, liquid water expands as it is heated because of areater molecular motion to form at 4C Figure 8.11 Between oC and 4'C the volume of liquid water decreases as the tempera- ture increases Above 4C, water behaves the way all other substances do: its volume increases as its temperature increases. The volumes shown here are for a 1-gram sample
Water is densest at 4℃ When the temperature of a given is increased, its molecules vibrate faster and move farther apart. So the substance expands. This is the case in all three phases of water, apart from the liquid water from 0-4℃. The reason is “ice-like” crystal structure starts to form at 4℃
The fact that water is densest at 4C is of great Importance in nature -IOC Ice C Liquid water 4C Figure 8.12 As water cools to 4C, it sinks. Then, as water at the surface is cooled to below 4C, it floats on top and can freeze. Only after surface ice forms can temperatures lower than 4C extend down into the pond. This does not happen very readily, however, because surface ice insulates the liquid water from the cold air
The fact that water is densest at 4℃ is of great importance in nature