Gases, Liquids, Solids, and Intermolecular Forces PDF

Chapter 5 Gases Chapter 11 Liquids, Solids, and Intermolecular Forces  Properties of the three Phases of Matter C A In St om W ttr te re p r il l...

Chapter 5 Gases Chapter 11 Liquids, Solids, and Intermolecular Forces  Properties of the three Phases of Matter C A In St om W ttr te re p r il l ac rm n es it tio o gth si F l n le bl ow s cu o f e? ? la State Shape Volume Density r Solid fixed fixed high No No very strong Liquid indefinite fixed high No Yes intermediate Gas indefinite indefinite low Yes Yes weak Fixed = keeps shape when placed in a container Indefinite = takes the shape of the container Three Phases of Water Gas Structure Gas molecules are rapidly moving in random straight lines and free from sticking to each other. Solids some solids have their particles arranged in an orderly geometric pattern – we call these crystalline solids salt and diamonds other solids have particles that do not show a regular geometric pattern over a long range – we call these amorphous solids plastic and glass Liquids  they have higher densities than gases because the molecules are in close contact  but they have a definite volume because the limit on their freedom keeps them from escaping the rest of the molecules Phase Changes  Gases Gas Gas pressure  Explaining the Properties of Liquids Liquids have higher densities than gases and are incompressible because the particles are in contact They have an indefinite shape because the limited translational freedom of the particles allows them to move around enough to get to the container walls It also allows them to flow But they have a definite volume because the limit on their freedom keeps the particles from escaping each other  Surface Tension Surface tension is a property of liquids that results from the tendency of liquids to minimize their surface area To minimize their surface area, liquids form drops that are spherical A trout fly can float on water because of surface tension  Because they have fewer neighbors to attract them, the surface molecules are less stable than those in the interior The surface tension of a liquid is the energy required to increase the surface area a given amount – surface tension of H2O = 72.8 mJ/m2 at room temperature – surface tension of C6H6 = 28 mJ/m2 20 Tro: Chemistry: A Molecular Approach, 2/e  Viscosity Viscosity is the resistance of a liquid to flow – 1 poise = 1 P = 1 g/cm∙s – often given in centipoise, cP H2O = 1 cP at room temperature Larger intermolecular attractions = larger viscosity  Factors Affecting Viscosity The stronger the intermolecular attractive forces, the higher the liquid’s viscosity will be The more spherical the molecular shape, the lower the viscosity will be – molecules roll more easily – less surface-to-surface contact lowers attractions Raising the temperature of a liquid reduces its viscosity – raising the temperature of the liquid increases the average kinetic energy of the molecules – the increased molecular motion makes it easier to overcome the intermolecular attractions and flow Insert Table 11.6  Capillary Action Capillary action is the ability of a liquid to flow up a thin tube against the influence of gravity – the narrower the tube, the higher the liquid rises Capillary action is the result of two forces working in conjunction, the cohesive and adhesive forces – cohesive forces hold the liquid molecules together – adhesive forces attract the outer liquid molecules to the tube’s surface  Capillary Action The adhesive forces pull the surface liquid up the side of the tube, and the cohesive forces pull the interior liquid with it The liquid rises up the tube until the force of gravity counteracts the capillary action forces The narrower the tube diameter, the higher the liquid will rise up the tube  Meniscus The curving of the liquid surface in a thin tube is due to the competition between adhesive and cohesive forces The meniscus of water is concave in a glass tube because its adhesion to the glass is stronger than its cohesion for itself The meniscus of mercury is convex in a glass tube because its cohesion for itself is stronger than its adhesion for the glass 26 Tro: Chemistry: A Molecular Approach, 2/e  Vaporization If these high energy molecules are at the surface, they may have enough energy to overcome the attractive forces – therefore – the larger the surface area, the faster the rate of evaporation This will allow them to escape the liquid and become a vapor  Condensation Some molecules of the vapor will lose energy through molecular collisions The result will be that some of the molecules will get captured back into the liquid when they collide with it Also some may stick and gather together to form droplets of liquid – particularly on surrounding surfaces We call this process condensation  Boiling Point When the temperature of a liquid reaches a point where its vapor pressure is the same as the external pressure, vapor bubbles can form anywhere in the liquid – not just on the surface This phenomenon is what is called boiling and the temperature at which the vapor pressure = external pressure is the boiling point  Boiling Point The normal boiling point is the temperature at which the vapor pressure of the liquid = 1 atm The lower the external pressure, the lower the boiling point of the liquid  Sublimation and Deposition Molecules in the solid have thermal energy that allows them to vibrate Surface molecules with sufficient energy may break free from the surface and become a gas – this process is called sublimation The capturing of vapor molecules into a solid is called deposition The solid and vapor phases exist in dynamic equilibrium in a closed container – at temperatures below the melting point – therefore, molecular solids have a vapor pressure sublimation solid deposition gas Sublimation