Chemistry Midterm 1 Study Guide.pdf

Chemistry Midterm 1 Study Guide.pdf - Chemistry The study...

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Chemistry The study of matter and its properties, the changes that matter undergoes, and the energy that is associated with those changes Matter: the "stuff" you can see, smell, taste and touch; anything with mass and volume Properties: the set of characteristics that give each substance its unique identity The macroscopic patterns and behavior of substances that we can see or easily measure are the result of atomic-scale (microscopic or sub-microscopic) properties and behavior Chemists use the observable changes in the properties/behavior of matter to understand their microscopic causes Chapter 4 4.1 Properties of Gases (overview of the physical states of matter) What is a gas? Fills and assumes the shape of its container Diffuses and mixes in all proportions with other gases Molecules of a gas are separated by large distances and interact weakly with each other, if at all o Wide separation -> weak intermolecular forces When you compare densities between solids, liquids and gases: o Gases are 1000x less dense than s and l o Gas density depends on T and P o s and l do experience thermal expansion But change is small in comparison with changes that gases undergo with T and P variations Variables/parameters that describe any gas : Number of moles o Proportional to mass Temperature Volume Pressure These 4 properties define state of a gas; there are strict dependencies and laws between them 4.2 Properties of Gases: Pressure and its Measurement Pressure Confined gases exert pressure Defined as an outwardly directed force on the walls that contain a gas Pressure = force per unit area o P (Pa) = !"#$% (() *#%+ (, - ) Pressure of one Pascal: o Force of 1 N (1 kg m/ . / ) spread over 1 0 / When comparing 2 objects of the same mass (weigh = force), the one exerting that force over a smaller surface area exerts higher P
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Barometric ( Atmospheric ) pressure : Effective mass of the atmosphere over 1 0 / = 10,340 kg Force exerted by this mass = 101,300 N P = 101,300 N / 1 0 / o One atmosphere of pressure = 101.3 kPa Evangelista Torricelli discovered atmospheric pressure and build world's first barometer Atmospheric pressure: o 760 mmHg o 760 torr o 1 atm o 101325 Pa o 101.325 kPa o 1.01325 bar Barometer Fill closed tube with Hg and invert the tube, then place open end in container of Hg -> height of Hg falls to 76 cm Hg level changes until pressure from Hg column = atmospheric pressure = 760 mm (sea-level) o Length of column does o not depend on diameter of tube Liquid pressure : Pressure exerted by a column of liquid at its base o P = h • d • g Pressure does not depend on the cross-sectional area of the column Pressure exerted by a liquid depends on: o Height of the column of liquid o Density of the column of liquid Manometer Measuring the pressure of a confined volume of gas 4.3 Simple Gas Laws Simple Gas Laws Relationships between pairs of gas properties (P, V, T, n) An "ideal gas" is a gas that obeys the simple gas laws perfectly Real gases can behave like ideal gases over a range of conditions
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