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?
8.1 Water molecules form an open crystalline structure in ice When water freezes, the water molecules arrange themselves in a SiX-Sided crystalline structure ncreased 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 ater 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 me 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 Ice Liquid water Aqueous solution of Nacl jure 8. (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℃ Water When the temperature of a given is increased ∞800402 Liquid water its molecules vibrate 0016 Temperature(C) faster and moⅴe 10014 farther apart. So the 10012 substance expands 10008 This is the case in all ihO three phases of water 10000 apart from the liquid water from0-4℃C.The Liquid water below 4C is bloated with ice crystals reason IS“ice-like UPon warming the crystals collapse, suiting in a smaller volume for the crystal structure starts liquid water. Above 4'C, liquid water expands as it is heated because of greater molecular motion to form at4℃. Figure 8.11 Between o/C and 4'C, the volume of liquid water decreases as the tempera- 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 4 is of great Importance in nature -IOC Ice oC Liquid water 4C Figure 8. 12 As water cools to 4 C, 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 lic iquid 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 °。。。° 9 Coin resting on the water surface, Why? Surface tension(表面张力 Surface tension(表面张力)The 9a9 tendency of the molecules on the surface of a liquid to go into the quid. The surface tension also Figure 8. 14 accounts for the spherical shape of A molecule at the surface is pulled only sideways and liquid drops, especiall the downward by neighboring molecules. A molecule beneath 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 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 Ai Nonpolar tail oap or detergent. molecule Polar head Water 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 water s 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 liquid and gaseous phases Evapora Condensation Liquid is Liquid water molecule Liquid water cooled a Liquid water Water vapor it loses this high-spee phase, having lost kinetic hydrogen bonding Figure 8.21 ches liquid surface. The exchange of molecules at the interface between liquid and gaseous water
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 release d uring 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 Figure 8. 27 As it condenses, the water vapor in humid tropical air releases ampl equivalent of about 32000 quantities of heat, Continued condensation can sometimes lead to powerful storm systems, such as hurricanes 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.)
