Chem 120 - Chemistry 120 Chapter 6: Gases Objectives -...

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Chemistry 120 Chapter 6: Gases Objectives - Understand and apply ideal gas laws o How do pressure, volume and temperature relate to the total amount of gas? o What about mixtures of different gases? o gases in chemical reactions. - Study the Kinetic-Molecular Theory of Gases o How does this explain the ideal gas law? - Non-ideal (real) gases o Molecules are big and sticky. 6-1 Properties of Gases - What is a gas? o fills and assumes the shape of its container. o diffuses and mixes in all proportions with other gases. - The molecules of a gas are separated by large distances and interact weakly with each other, if at all. - There are four essential parameters that describe any gas: o number of moles proportional to mass o temperature o volume o pressure - Confined gases exert pressure. - Detected as an outward force Pressure - P (Pa) = Force (N)/Area (m^2) - Force per unit area - Pressure of one Pascal: o Force of gravity: g = 9.8 m s^-2= 9.8 N kg^-1 o A 102 g object experiences a gravitational force of 1 Newton. o If this force is spread over 1 m2, the pressure is 1 Pascal. Barometric (Atmospheric) Pressure - Evangelista Torricelli - 1608-1647 (Northern Italy) - Discovers atmospheric pressure - Builds world’s first barometer - Fill closed tube with Hg (mercury). - Invert the tube.
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- Place open end in container of Hg. - Height of Hg falls to 760 mm. - Hg level changes until pressure from Hg column = atmospheric pressure - Always ≈760mm o does not depend on diameter of tube. - Atmospheric pressure: o 760 mmHg, 760 torr, 1 atm, 101325 Pa, 101.325 kPa, 1.01325 bar - This explains the engineers’ problem o water will rise until the pressure under the water column = 1 atmosphere = 101.325 kPa Liquid Pressure - Pressure exerted by a column of liquid. o Volume = A·h o mass = V·d= A·h·d o Force = m·g= A·h·d·g o Pressure = F/A = A·h·d·g/A = h·d·g Pressure does not depend on the area of the column Summary - Gases can be described by o n, T, V, P - Pressure = Force/Area - Pressure at the bottom of a liquid column depends only on the density and height (not area). - Atmospheric Pressure: o 101.325 kPa = 760 mmHg (torr) 6-2 Simple Gas Laws - All the simple gas laws are approximations. - An “ideal gas” is a hypothetical substance that obeys the gas laws perfectly. - Real gases can behave like ideal gases under the right conditions, as we shall see in more detail later. .. - Torricelli’s barometer (1643) allowed gas pressure to be measured for the first time. - In principle, a barometer can be placed inside a closed container of gas to measure pressure. o This is not practical. - Solution: convert the Barometer to a Manometer. Boyle’s Law - In 1662, Charles Boyle discovers the first gas law using a manometer. - Varies the volume and pressure of a fixed sample of air.
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Chem 120 - Chemistry 120 Chapter 6: Gases Objectives -...

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