《Lecture1-Introduction-water1》.ppt

Hydrogen bonds form when the positive end of one water molecule bonds to the negative end of another water molecule. Two important properties of water molecules: Cohesion(凝聚性) – the ability of water molecules to stick to each other, creating surface tension. Adhesion(吸附性) – the tendency of water molecules to stick to other materials. Hydrogen Bonds Water and Ocean Structure Heat Capacity of Water The quantity of heat required to raise the temperature of a substance by 1oC. Heat Capacity for Common Substances why does water have high heat capacity? Heat Capacity of Water Governed by water molecular processes Addition of heat: breaks H bonds first, then temperature rises Removal of heat: H bonds form, energy releases to prevents a rapid temperature drop Polarity(+/-): keeps molecules together The higher heat capacity, the more heat is required to raise the temperature. Physical properties of water related to heat are important: temperature mediation heat redistribution weather/climate This is because water has high heat capacity! Heat Capacity of Water Water has a very high heat capacity compared to land High heat capacity causes slow temperature changes in world’s ocean Helps keep the Earth’s surface temperature stable Heat Capacity of WaterSurface Water Moderates Global Temperature * * Latent Heat潜热 Latent Heat of Fusion Latent Heat of Vaporization Amount of heat needed to change from a solid to a liquid Amount of heat needed to change from a liquid to a vapor Water is the only substance that naturally occurs in all 3 states * Latent Heat Latent heat of vaporization (evaporation) is far greater than latent heat of fusion (melting). All of the H bonds between H20 molecules must be broken to form vapor Water - freezes 0°C; boils 100°C Water also helps moderate global temperatures by redistributing equatorial heat poleward * Viscosity of Water The resistance of fluid to flow Water has low viscosity Affected by temperature: T increase