Empirical Properties Of Gases Section 4.1 Pg. 148-154 Objectives: Introduce the empirical properties of gases Describe STP and SATP in terms of pressure and temperature Convert between Celsius and Kelvin temperature scales

Gases All gases have different _____________ properties but similar ____________ properties Chemical Properties: Gases are either:

Gases Physical Properties: Regardless of chemical properties, all gases: Always ______ their container (have no definite shape or volume) Are highly ______________ (increase pressure = decrease volume) ____________ through any available space Have volume and/or pressure affected by ______________ temperature volume (if container can expand) temperature pressure (if the container is a set volume)

Gases Gas – empirically, it is a substance that: Pressure – Fills the shape of any container Diffuses rapidly Mixes with other gases easily in pressure and/or volume when heated in pressure with increase in volume Pressure – Unit: kPa (kilopascal) or atm (atmosphere) caused by the _______________ of gas particles with the sides of the container

Practical Use for Understanding Pressure When you wear snowshoes, the force is distributed over the surface area of the snowshoes, so you exert less pressure on the ground than you would if you wearing regular shoes. This allows you to walk over snow instead of sinking into it.

Atmospheric Pressure

Atmospheric Pressure Pressure exerted by air on all objects Standard Temperature and Pressure (STP) = 101.325 kPa (use 101 kPa) and 0°C But laboratory temperatures are not at 0°C So scientists agreed on another set of conditions... Standard Ambient Temperature and Pressure (SATP) = 100 kPa and 25°C Much closer to lab conditions – so scientists don’t freeze

Atmospheric Pressure Units of Pressure What happens when you need to convert between units of pressure ?????

Dimensional Analysis Convert 5 torr to atm Convert 690 mm Hg to kPa and atm

Q: Where did 101.325 kPa come from? At sea level, average atmospheric pressure is about 101kPa. Scientists used this value to define one standard atmosphere (1 atm) as 101.325kPa Scientists have also used a mercury barometer to measure atmospheric pressure so standard pressure is also defined at 760 mm Hg 101.325 kPa = 1 atm = 760 mm Hg

When a tube filled with mercury is inverted, the weight of the column of mercury pulls it toward Earth. However, the weight of the air directly above the open dish pushes down on the surface of the mercury and prevents all of the mercury from falling out of the tube. The two opposing forces balance each other when the height of mercury is about 760 mm. If the vertical mercury filled tube is longer than 760 mm, the mercury drops to 760 mm.

WHY?? A student took a photo of an empty soda bottle at a rest area in the Rocky Mountains. Their GPS helped determine the altitude. When they returned to sea level the bottled collapsed because of the air pressure.  WHY?

WHY?? Marnie & Deanna are collecting air pressure readings for a class project. Marnie is recording her data near sea level. Deanna chose to hike to the top of a nearby mountain. Where is the air pressure greater? The picture shows how much more air is in the column above Marnie than above Deanna. The air pressure at sea level is greater than at Deanna's elevation.

Temperature How hot or cold an object is? No, not really... It’s the _______________ kinetic energy of the particles of a substance Absolute zero – the lowest temperature that can be obtained; the kinetic energy of all entities of solids, liquids or gases would become zero Kelvin temperature scale - absolute zero is zero Kelvin (0 K = -273 °C) Celsius temperature scale – zero is when water freezes (273 K = 0 °C)

Comparing Kelvin and Celsius Scales To convert degrees Celsius to Kelvin , you add 273. K = °C + 273 To convert Kelvin to degrees Celsius, you subtract 273. °C = K - 273 Examples: What is 254 K in °C ? What is -34°C in K ?

So do STP and SATP change? Yes – using Kelvin you have different numbers to use: Standard Temperature and Pressure (STP) = 101 kPa and 0°C = 101 kPa and 273.15K (use 273K) Standard Ambient Temperature and Pressure (SATP) = 100 kPa and 25°C = 100 kPa and 298.15 K (use 298K) Much closer to lab conditions – so scientists don’t freeze

PRACTICE Pg. 150 #1-3 Remember: 101.325 kPa =1 atm =760 mm Hg Pg. 154 # 11-13 Remember: T (K) = t (°C) + 273