7-6 Mass to Volume Problems (13.10)

  At STP 1 mole of any gas will occupy 22.4 L of volume Sometimes a reaction will produce a gas and the chemist needs to know the volume collected. For example, KClO3 decomposes upon heating by the following reaction: 2KClO3(s) → 2KCl(s) +3O2(g) What volume of oxygen can be obtained by decomposing 175g KClO3 at 20ºC and 750 mmHg?

2KClO3(s) → 2KCl(s) +3O2(g) First calculate the moles of O2 produced: ? 2KClO3(s) → 2KCl(s) +3O2(g) ? 175 g 122.55 g/mol First calculate the moles of O2 produced: 175 g KClO3 ( 1mol/122.55g) (3 O2 / 2 KClO3) = 2.14 mol. O2 produced Next, use PV = nRT to calculate the volume: 750 (?) = 2.14 (62.4) 293 = V = 52.2L

7-7 Volume to Volume Problems At STP 1 mole of any gas will = 22.4 L For reaction with only gases, the moles and volumes are in the same ratio (Avogadro’s Principle): ? ? 10L ? C5H12(g) + 8O2(g) → 5CO2(g) + 6H2O(g)  What volume of C5H12(g) and O2(g) are needed to produce 10L of carbon dioxide? 2 16 10 12

7-8 Kinetic Molecular Theory KMT (Sections 13.8, 13.9) KMT provides an atomic level explanation for the macroscopic properties of gases. The theory is designed to describe an “ideal gas”, that is, one that obeys PV=nRT. There are 5 components to the theory:

5 components to the theory: Gases consist of tiny particles (atoms or molecules). These particles are so small, compared to the distances between the, that the volume (size) can be assumed to be negligible (zero). The particles are in constant random motion, colliding with the walls of the container. These collisions cause the pressure exerted by the gase. The particles are assumed NOT to attract or to repel each other. The average kinetic energy of the gas particles is directly proportional to the Kelvin temperature of the gas.

The Ideal Gas Law works best at low pressures and high temperatures. Under these conditions the particles are farther apart (less pressure) and any attraction between them can be overcome by their high velocities (high temperature).  

7-9 Diffusion Diffusion is the term used to describe the mixing of gases. At a given temperature, molecules have the same average kinetic energy. Since KE = ½ mv2, larger mass molecules will diffuse more slowly than smaller ones.

Why does the solid precipitate of ammonium chloride form closer to the HCl than the ammonia? 17.03 amu 36.46 amu