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Lecture 2

CHEM 151 Lecture 2: Chem 151- Unit 1 Module 2

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CHEM 151

Chemistry Unit 1 Module 2 Modeling Matter ● Task of differentiating substances simplified by development of models about their internal structure ● Most substances are made up of particles nano-size ● Particulate model of matter: all substances are composed of small particles in constant movement ● Assumption 1: any macroscopic sample of a substance is composed of an extremely large number of very small identical particles (1 mL water → 3.34 x 10^22 particles) ● Assumption 2: particles of matter are constantly moving in random directions through empty space (Pressure is determined by the force of the particle collisions on the walls → Pressure=Force/Area, Temperature determines the speed) The average speed of particles depends on 2 main things: the temperature of the system (T) and the mass of the individual particles (m) Temperature → Average Kinetic Energy: < Ek > = ½ m ^2 (v = average particle speed) *Particles of the same substance in two different coexisting phases at a certain temperature will have the same average kinetic energy and thus the same average particle speed independently of the state of matter ● Assumption 3: Particles interact with each other and the strength of these interactions depends on distance *Most substances become gases at high temperatures and low pressures Pressure is proportional to number of particles (n up, P up) Pressure is proportional to temperature (T up, P up) Pressure is inversely proportional to volume ( 1/V , 1/x graph) P = kB (NT/V) , kB = 1.380 x 10^-23 J/K Boltzmann c
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