CHEM 122 1st Edition Lecture 4Outline of Last Lecture I. Ion-Dipole forcesII. Properties of Liquidsa. Viscosityb. Surface tensionIII. Adhesive/Cohesive Forcesa. Capillary ActionIV. Phase Changesa. Energy changesOutline of Current Lecture I. Molar Heat CapacityII. Evaporation of a LiquidIII. Vapor PressureIV. Boiling of a Liquida. Effect of Pressure on Boiling Point.Current LectureMolar heat capacity: heat energy required to raise the temperature of 1 mole of a substance to 1 degree C. - Solid ice= 37.6 J/(mol* C)- Liquid water= 75.2 J/ (mol* C)- Steam= 33.1 J/(mol* C)Evaporation of a Liquid:What facorseffect the speed of evaporation?1. Surface area of the liquid- the bigger the surface area the faster speed of evaporation2. Tempurature of the liquid- the higher the temperature the faster speed of evaporation3. Strength of intermolecular forces- the weaker intermolecular forces the faster speed of evaporation.These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Requirements for vaporization of a liquid molecule:1. The molecule must be at the surface- bigger the surface area the more molecules at the surface meaning the more molecules can escape the liquid.2. Molecules must have enough kenetic energy to break the intermolecular forces of attraction. *Only the molecules whose kenetic energy exceeds the intermolecular forces of attraction can escape the liquid to form a gas.*- If the temperature is increased then the kenetic energy is increased then more molecules are allowed to exceed the intermolecular forces of attractionVapor Pressure:pressure exerted by the vapor when the rate of vaporization and rate of condensation are equal. Vapor pressure only depends on the temperature and strength of intermolecular forces.When a liquid is placed in an air tight chamber some of the liquid evaporates yielding a vapor that exerts a pressure on the container walls.- As temperature increases, vapor pressure also increaseso This happens because when temperature increases the kenetic energy increases and a greater percentage of molecules have a kenetic energy greater than the intermolecular forces, allowing them to escape into a vapor.- At a fixed temperature vapor pressure increases as the intermolecular forces decreaseCondensation: When gas molecules collide with the liquid surface and are captured.- As more liquid evaporates the pressure of the gas increases causing the condensation to increase and EVENTUALLY… Rate of evaporation=Rate of condensation.Boiling point of a Liquid: A liquid boils when vapor bubbles form within the liquid and escape.- When the vapor bubbles forms, the pressure exerted by the bubble is equal to the vapor pressure of the liquid at that temperature. - If the external pressure above the surface is greater than the vapor pressure the vapor bubble with collapse.- If the vapor pressure is equal or greater then the external pressure then the bubble will quickly escape to the surfaceNormal Boiling Point: The temperature at which the vapor pressure is equal to 1 atm (atmospheric pressure)- Increase in pressure-increase in boiling pointo The food can be cooked to a higher temperature, cooking the food faster- Decrease in pressure-reduce boiling pointo When boiled, it will be a lower temperature, taking longer to cook the
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