OB: Intro to phases chemistry

1. OB: Intro to phases chemistry The three states of matter Solids, liquids, and gases, and Changing from phase to phase.

2. Matter comes in three phases, and we know that the matter can change from phase to phase. We’ll soon learn how and why this happens. There are six phase changes that you need to know always: Melting/freezing boiling/condensing Sublimation/deposition Energy is associated with the phases as well Gases have the highest energy, solids the lowest. Water is our most common substance, and therefore we need to always be aware of the temperatures that the phase changes occur at (at normal pressures).

3. Temperature chart for water at normal pressure. 373 K = 100°C 273 K = 0°C 0 K = absolute zero

4. Temperature chart for water at normal pressure. Gas phase 373 K = 100°C Steam condenses, water vaporizes Liquid phase 273 K = 0°C Ice melts, water freezes SOLID phase 0 K = absolute zero

5. Water is weird, because it’s common to us in all 3 phases. Most substances are not normally seen in all 3 phases in the normal temperatures that we live in. For example:

6. Although most of us wouldn’t realize this, pressure is influenced by the air pressure as well. Just like most fish don’t know they’re wet, we don’t often realize the effect that the air has on us or everything else.

7. Air pressure is measured with three unusual units… • Atmospheres of pressure (atm). One atmosphere is the normal amount of air above us, so 1.0 atm is considered “normal” air pressure. • Millimeters of Mercury (mm Hg) is next. I’ll show you tomorrow how the original barometers worked, how they measured air pressure. “Normal” was when the mercury rose up to a height of 760 mm. • Kilo-pascals (kPa) is last, and most metric. We’ll use this one the most, and we’ll get used to the funky names.LOOK now at table A on the reference tables. Normal temperature is both 273 Kelvin or 0°C, and • Normal Pressure is 101.3 kPa, or 1.0 atm. (It’s also 760. mm Hg)

8. Time for a fun demo of air pressure (or two). First, notice I have nothing up my sleeves. I need one of those hats! First, let me tell you that “normal” air pressure is sometimes still measured in pounds per square inch or psi. Normal pressure is 14.7 psi. I just happen to have a hunk of steel that’s 1 square inch on the bottom and 14.7 pounds.

9. Next, let’s notice the force of the air pressure that we never even notice. Here’s a water glass, like the one in my hand. The top is about 2 inches across, and with that Area of a circle formula = πr2 A = (3.14) x (1 inch) x (1 inch) = about 3.14 in2 My water is about a pound, so the pressure that this water would create if I turned it upside down would be slight (about 0.4 psi) WATCH! Think!

10. Water pressure pushes down, about 0.4 psi Which is stronger? Air pressure pushes up (14.7 psi)

11. Air pressure conversions, using the “normal” air pressure equalities 101.3 kPa = 760. mm Hg = 1.0 atm Let’s convert higher than normal air pressure of 145 kPa into atmospheres.

12. Air pressure conversions, using the “normal” air pressure equalities 101.3 kPa = 760. mm Hg = 1.0 atm Let’s convert higher than normal air pressure of 145 kPa into atmospheres. 145 kPa1 1.0 atm101.3 kPa X =1.43 atm

13. thirteen

14. The pressure in a balloon is 905 mm Hg. What’s that in kilopascals?

15. The pressure in a balloon is 905 mm Hg, what’s that in kilopascals? 905 mm Hg1 101.3 kPa760. mm Hg X = 121 kPa