Module-2B.pdf

MODULE 2B: STATES OF MATTER THE LIQUID PHASE  LIQUID PHASE The liquid state is defined by comparison to the gaseous and solid states. Liquids are denser than gases and possess less kinetic energy than do gases. They are considered less compressible than gases and more compressible than solids....

MODULE 2B: STATES OF MATTER THE LIQUID PHASE  LIQUID PHASE The liquid state is defined by comparison to the gaseous and solid states. Liquids are denser than gases and possess less kinetic energy than do gases. They are considered less compressible than gases and more compressible than solids. Due to the intermolecular forces between liquid particles, which are weaker than solids but stronger than gases, they have the ability to flow but have very limited compressibility. PROPERTIES OF LIQUIDS Little kinetic energy. They collide with one another and with their container walls. These collisions between liquid particles involve transfer of energy. When enough energy has been transferred to the particles at the surface of the liquid, those particles will eventually overcome the surface tension and escape the system in the form of vapor. Since we know that gas particles move in a faster rate than those of the liquid, an input of energy is required to convert liquid to gas. The most common way to add energy in a system is through heating. Take note that a liquid does not have to be heated to its boiling point before some of the particles become gas or vapor because those particles already have enough kinetic energy to escape from their liquid state. VAPOR PRESSURE is a physical property of liquids. Equilibrium vapor pressure does not depend on the volume of weight of the liquid or the atmospheric pressure or the presence of other vapors in the air VAPOR PRESSURE Vapor pressure is the pressure of the gas or vapor above a liquid in a closed container. Equilibrium vapor pressure is the pressure of the saturated vapor above the liquid. Only when the rate of condensation and rate of evaporation achieve equilibrium will the vapor be considered as saturated. As the temperature of the liquid is elevated, more molecules approached the velocity necessary to pass into the gaseous state. As a result, the vapor pressure rises with the temperature. If the temperature of the liquid increases while maintaining a constant pressure, or if the pressure decreases while keeping the temperature constant, all liquid will pass into the vapor state. VAPOR PRESSURE CLAUSIUS- CLAPEYRON EQUATION explains the relationship between the vapor pressure and the absolute temperature of a liquid CLAUSIUS- CLAPEYRON EQUATION If a liquid is placed in an open container and heated until the vapor pressure equals the atmospheric pressure, the vapor will form bubbles that rise rapidly through the liquid and escape into gaseous state. The temperature in which the vapor pressure is in equilibrium with the atmospheric pressure is the boiling point. It is also considered as the temperature at which the thermal agitation overcomes the attractive forces between the molecules of the liquid which can give us a rough indication of the magnitude of the attractive forces present in a liquid.  Boiling points of hydrocarbons, simple alcohols, and carboxylic acids increase with molecular weight due to the increase in van der Waals forces with the increase in atoms. Branching of the hydrocarbon chains produces a less compact molecule with reduced intermolecular attraction resulting to a decrease in boiling point. CALCULATORS IN! THE VAPOR PRESSURE OF A SUBSTANCE IS 21 TORR AT 300K. CALCULATE VP AT 310 K IF THE ENTHALPY OF VAPORIZATION IS 24KJ/MOL THE VAPOR PRESSURE OF A SUBSTANCE IS 30 TORR AT 250K. AT WHAT TEMPERATURE WILL THE SUBSTANCE HAVE A VP OF 150 TORR. ENTHALPY OF HVAP = 45KJ/MOL Carbon tetrachloride has a vapor pressure of 213 torr at 40.0 °C and 836 torr at 80.0 °C. What is the enthalpy of vaporization in kJ/mol? THE VAPOR PRESSURE OFA SUBSTANCE IS AT 0.2ATM AT 100DEGC. IF ITS HEAT OF VAPORIZATION IS 30KJ/MOL, CALCULATE VP AT 50 DEGC T H A N K Y O U ! R E A D Y F O R M O D U L A R Q U I Z