Chapter 10 States of Matter

1. Chapter 10States of Matter 10.1 The nature of gases

2. Things you will learn • You will understand the motion of gas particles according to the kinetic theory. • You will be able to interpret gas pressure in terms of kinetic energy and absolute temperature.

3. Gases we’re used to • O2 • CO2 • N2 • He • N2O • Ar

4. Most gases are molecular, not ionic;They’re from the group of non-metals

5. Things we might know about gases • Lightweight • Compressible • Transparent • Fills a container completely, like liquids do • Disperses smells • Supports flames or is flammable

6. Kinetic theory of gases(atoms in all forms of matter are in motion) • A gas is composed of small hard spheres with insignificant volume separated by large empty spaces. No attractions or repulsions exist between particles.

7. Kinetic theory of gases(atoms in all forms of matter are in motion) 2. The particles in a gas move rapidly in constant random motion. Their short-term motion is in a straight line. Gases fill their containers regardless of shape. Uncontained gases disperse.

8. Kinetic theory of gases(atoms in all forms of matter are in motion) 3. All collisions are perfectly elastic. Kinetic energy is transferred between particles such that the total kinetic energy remains constant.

9. Kinetic theory of gases(atoms in all forms of matter are in motion) • Small hard particles • In constant random motion • Collisions elastic – EK remains constant

10. Gas pressure • Collisions of lots of very small particles on a surface will exert a force on that surface • Pressure is the measure of that force • Pressure =force/area • When there are no particles present, there is no force. This is called a vacuum.

11. Low pressure area on human being

12. Gas pressure • The units of pressure are called Pascals • This is Newtons (force) / meters2 (area) • A newton is about 102 grams of force • Pressure at sea level is 101.3 kPa

13. Equivalent terms of standard pressure • Pressure at sea level is • 101.3 kPa • 1 atm • 760 mm Hg ; 29.9 in Hg • 14.7 lbs/in2

14. Gravity holds all the earth’s atmosphere near the surface, but the pressure of the atmosphere depends only on what is stacked above it, so pressure goes down as you go up in elevation (so air down lower is denser)

15. Barometers • Barometers are instruments which measure pressure • Atmospheric pressure was originally measured with a glass tube filled with mercury • Newer barometers use calibrated springy metal diaphrams

16. Mercury barometer

17. Aneroid barometer

19. Lord Kelvin discovered that when you raise or lower the temperature of a gas by 1°C, you change its volume slightly.Working backwards, he was able to determine an absolute temperature scale where the volume of a gas theoretically went to zero!!!

20. Kelvin temperature scale • Kinetic theory has to do with the motion of particles • Temperature is a measure of the average kinetic energy of a bunch of particles • Kelvins are the same “size” as degrees centigrade • Kelvins are directly related to kinetic energy and pressure of a gas • Kelvins are °C + 273!

22. Average kinetic energy

23. STP standard temperature and pressure • Pressure - sea level pressure • 101.3 kPa (we’ll use 100 kPa) • 760 mm Hg • 1 atm • 14.7 lbs/in2 • Temperature – freezing point of water • 273 K • 0°C Equivalent terms Equivalent terms

24. A gas is at a pressure of 1.50 atm. What is its pressure in: • kiloPascals • millimeters of mercury

25. Express the pressure 545 mm mercury in : • kiloPascals • atmospheres

26. A cylinder of gas is at 85C and 60 atm. pressure. What is the pressure if the temperature is raised to 185C?

27. Sim # 2