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
8.3 The behavior of liquid water is the result of the stickness of water molecules Cohesive force(内聚力) forces of attraction between molecules of a single substance Adhesive force(粘合力): forces of attraction between molecules of two different substances 。。° Coin resting on the water surface. Why? Sur/ ace tension(表面张力) Surface tension(表面张力)The tendency of the molecules on the surface of a liquid to go into the 99 liquid. The surface tension also Figure 8. 14 accounts for the spherical shape of A molecule at the surface is pulled only sideways and liquid d downward by neighboring molecules. A molecule beneath pecially in the the surface is pulled equally in all directions weightless environment
8.3 The behavior of liquid water is the result of the stickness of water molecules Cohesive force ( 内聚力): forces of attraction between molecules of a single substance. Adhesive force ( 粘合力): forces of attraction between molecules of two different substances. Coin resting on the water surface, Why? Surface tension (表面张力) Surface tension ( 表 面 张 力 ): The tendency of the molecules on the surface of a liquid to go into the liquid. The surface tension also accounts for the spherical shape of liquid drops, especially in the weightless environment
Water has very high sur face tension because of the strong hydrogen bond, which prevents it from wetting materials with nonpolar surfaces, such as waxy leaves, umbrellas. The addition of detergent (or) soap can reduce the surface tension and increase the wettability of water Air Nonpolar tail oap or detergent molecule Polar head Wa Figure 8.16 Soap or detergent molecules align themseles at the surface of liquid water so that their nonpolar tails can escape the polarity of the water. This arrangement disrupts the waters surface tension
Water has very high surface tension because of the strong hydrogen bond, which prevents it from wetting materials with nonpolar surfaces, such as waxy leaves, umbrellas. The addition of detergent (or) soap can reduce the surface tension and increase the wettability of water
Capillary action(毛细管作用) results from the interplay of adhesive and cohesive forces Adhesive forces Cohesive forces Adhesive forces Cohesive forces Figure 8 19 Water is drawn up a narrow glass tube by an interplay of adhesive and cohesive forces
Capillary action (毛细管作用) results from the interplay of adhesive and cohesive forces
8.4 Water molecules move freely between the quid and gaseous phases ① Liquid water molecule② Liquid water cooled as③ Molecule enter9 gaseous Liquid water Water vapor ergy to overcome water molecule Figure 8.21 surface hydrogen bonding approaches liquid sur face e liquid surface. Air is The exchange of molecules at the interface between liquid and gaseous water. slowly moving gaseou
8.4 Water molecules move freely between the liquid and gaseous phases
Evaporation(蒸发) is a cooling process. Condensation(凝聚) is a warming process A large amount of energy is released d urn g the condensation of water vapor Household radiator Hurricanes(The formation of 1 inch of rain over an area of 1 square mile yields the energy 7 As it condenses, the water vapor in humid tropical air releases ample equivalent of about 32000 s of heat. Continued condensation can sometimes lead to powerful systems, such as hurricane tons of exploded dynamite
Evaporation (蒸发) is a cooling process. Condensation (凝聚) is a warming process. A large amount of energy is released during the condensation of water vapor. Household radiator Hurricanes (The formation of 1 inch of rain over an area of 1 square mile yields the energy equivalent of about 32000 tons of exploded dynamite.)
