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Physical properties

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Physical properties

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    1. Physical properties Solids, liquids and gases can be identified and distinguished bases on physical properties Density, shape, compressibility, thermal expansion Density is the ratio of the mass of a sample of matter divided by the volume of the same sample. Shape depends on the physical state of matter. Independent of container for solids Dependent on shape of container for liquids and gases Compressibility is the change in volume of a sample of matter that results from a pressure change acting on the sample. http://www.qualatex.com/pages/micro_helium_ase.php

    2. Physical properties Thermal expansion is the change in volume of a sample of matter resulting from a change in the temperature of the sample.

    3. Kinetic Molecular Theory of Matter Postulate 1: Matter is made up of tiny particles called molecules. Postulate 2: The particles of matter are in constant motion and therefore possess kinetic energy. Postulate 3: The particles possess potential energy as a result of repelling or attracting each other. Postulate 4: The average particle speed increases as the temperature increases. Postulate 5: The particles transfer energy from one to another during collisions in which no net energy is lost from the system.

    4. Kinetic and Potential Energy Kinetic energy is the energy a particle has as a result of being in motion. Potential energy is the energy a particle has as a result of being attracted to or repelled by other particles. A cohesive force is an attractive force between particles. It is associated with potential energy. (Temperature independent) A disruptive force results from particle motion. It is associated with kinetic energy. (Temperature dependent)

    5. Solid state High density- closely packed Definite shape independent of its container- strong cohesive forces Small compressibility- little interparticle space, little effect of pressure Very small thermal expansion- increased amplitudes only “occupy” larger volume

    6. Liquid state High density-randomly but close together (touching) Indefinite shape depends on the shape of its container – free to move randomly Small compressibility- essentially touching, very little space Small thermal expansion- slight volume change, increased particle velocity

    7. Gaseous state Low density- Widely spread particles Indefinite shape- free to travel in all directions Large compressibility- Mostly empty space, pressure pushes particles closer Moderate thermal expansion- more collisions with more energy, large volume

    8. Gas Laws Gas Laws- mathematical equations that describe the behavior of gases as they are mixed, subjected to pressure or temperature changes, or allowed to diffuse. The pressure exerted on or by a gas sample and the temperature of the sample are important quantities in gas law calculations. Pressure is defined as a force pushing on a unit area of surface on which the force acts. Eiffel tower- 7000+ tons, pressure equivalent of an adult sitting on a chair (~50 pounds per sq. inch)

    9. Pressure and temperature units One standard atmosphere- pressure needed to support a 760-mm (76.0-cm) column of mercury in a barometer tube. 1 torr of pressure is the pressure needed to support a 1-mm column of mercury in a barometer tube. Absolute zero on Kelvin scale- temperature at which kinetic energy = 0 (motion stops). K = 273 + °C

    10. Boyle’s Law Sir Robert Boyle- Irish chemist observed at constant temperature product of pressure and volume of a gas sample stays nearly constant Mathematically or P- pressure V-volume k- experimental constant Application: Scuba diving

    11. Charles’s Law Jacques Charles studied temperature and volume behavior at constant pressure. Volume of gas sample at constant pressure directly proportional to its temperature Mathematically or T- Temperature k’- experimental constant Application: Balloons

    12. Combined Gas Law Boyle’s and Charles’s laws combined to give P,V,T relationship of a gas sample Mathematically k”- experimental constant Consider a gas sample at initial Pi, Vi, Ti For this sample If the sample pressure, volume and temperature are changed to Pf, Vf, Tf Hence,

    13. Combined Gas Law Example: A gas sample has a volume of 2.50 liters when it is at a temperature of 30.0°C and a pressure of 1.80 atm. What volume in liters will the sample have if the pressure is increased to 3.00 atm, and the temperature is increased to 100°C? Learning check 6.6

    14. Ideal Gas Law Combined gas law gives relationship for fixed mass of gas sample Avogadro’s law: Equal volumes of gases measured at the same temperature and pressure contain equal number of molecules At Standard Temperature [0 °C = 273 K] and Pressure [1.0 atm] (STP)- 1 mol of a gas occupies 22.4 L Ideal Gas Law The ideal gas law allows calculations to be done in which the amount of gas varies as well as the temperature, pressure and volume. Mathematically, the ideal gas law is written as follows: PV= nRT n- number of moles R- Universal gas constant =

    15. Ideal Gas Law Example 6.8 A 2.50 mole sample of gas is confined in a 6.17 liter tank at a temperature of 28.0°C. What is the pressure of the gas in atm? Alternatively, ideal gas law can be written as- Learning check 6.8

    16. Dalton’s Law of Partial Pressures John Dalton- English schoolteacher experiments led to the law- the total pressure exerted by a mixture of gases is equal to the sum of the partial pressures of the gases in the mixture. The partial pressure of an individual gas of a mixture is the pressure the gas would exert if it were confined alone under the same temperature and volume conditions as the mixture Learning check 6.9

    17. Changes in State

    18. Evaporation, Condensation, Vapor Pressure Evaporation or vaporization is an endothermic process in which a liquid is changed to a gas. Deposition or condensation is an exothermic process in which a gas is changed into a liquid or solid. Vapor Pressure is the pressure exerted by a vapor that is in equilibrium with its liquid. (Table 6.4, 6.5)

    19. Boiling and boiling point The boiling point of a liquid is the temperature at which the vapor pressure of the liquid is equal to the prevailing atmospheric pressure. Normal or standard boiling point- 1 standard atm Pressure cooker- higher pressure ? higher temperature

    20. Sublimation and Melting SUBLIMATION Sublimation is an endothermic process in which a solid is changed to a gas without first melting to a liquid. MELTING OR FUSION Melting or fusion is an endothermic process in which a solid is changed to a liquid.

    21. Energy and States of Matter The specific heat of a substance is the amount of heat required to raise the temperature of exactly 1 g of a substance exactly 1°C.

    22. Energy and States of Matter Heat absorbed/released= (mass) (specific heat) (temperature change) HEAT OF FUSION The heat of fusion of a substance is the amount of heat required to melt exactly 1g of a solid substance at constant temperature. HEAT OF VAPORIZATION The heat of vaporization of a substance is the amount of heat required to vaporize exactly 1g of a liquid substance at constant temperature. Learning check 6.13, 6.14

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