•1 CHEM 1000 3.0 Gases 1 Gases • Petrucci, Harwood and Herring: Chapter 6 CHEM 1000 3.0 Gases 2 • We will be looking at Macroscopic and Microscopic properties: – Macroscopic • Properties of bulk gases • Observable – Pressure, volume, mass, temperature… – Microscopic • Properties at the molecular level • Not readily observable – Mass of molecules, molecular speed, energy, collision frequency
•2 CHEM 1000 3.0 Gases 3 Macroscopic Properties • Our aim is to look at the relationship between the macroscopic properties of a gas and end up with the gas laws CHEM 1000 3.0 Gases 4 Pressure • To contain a gas you must have a container capable of exerting a force on it (e.g. the walls of a balloon). • This implies that the the gas is exerting a balancing force • Normally we talk about the pressure (force/area) rather than force
•3 CHEM 1000 3.0 Gases 5 Measuring Pressure • The simplest way to measure gas pressure is to have it balance a liquid pressure. • Therefore we need to quantify the liquid pressure CHEM 1000 3.0 Gases 6 A h • Consider a cylinder of liquid with area A and height h • The force exerted at the bottom of the cylinder is its weight F = m.g • The pressure exerted is P = F/A = m.g/A • The density of the liquid is d=m/V and m = d.V but V=A.h • So P = m.g/A = g.V.d/A = g.A.h.d/A = g.h.d
•4 CHEM 1000 3.0 Gases 7 Barometer To measure Atmospheric Pressure On the left the tube is open On the right the tube is closed
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