Gases. I.Real Gases (we will not study these much) A. Do NOT apply the Kinetic Molecular Theory 1. The particles in a real gas can NOT be thought of as.

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Presentation transcript:

Gases

I.Real Gases (we will not study these much) A. Do NOT apply the Kinetic Molecular Theory 1. The particles in a real gas can NOT be thought of as small, well spread points in space. 2. The particles in a real gas have significant volume and tend to be closer together. 3. Interactions between the particles in a real gas are NOT negligible.

Kinetic Theory of Matter All particles are in constant motion: –The faster the particles move, the more heat the substance will have. –The slower the particles move, the less heat the substance will have. Add Heat

The opposite is true too: –When heat is removed particles get slower and move closer together Remove Heat

How can you identify a real gas? Gases at low temperature tend to act as real gases. Gases at high pressure tend to act as real gases. Gases of larger or more polar particle units tend to act as real gases. Fundamentally, a real gas acts as though it is approaching the liquid phase. The particles are slowing down (low temperature) and moving closer together (high pressure).

II. Ideal Gases (we WILL study these a lot!) 5 Assumptions of an ideal gas: 1. Gas consists of large #’s of particles that are far apart relative to their size. - most volume occupied by gas is empty space 2. Collisions between ideal gas particles are elastic (the particles don’t lose energy). 3. Ideal gas particles are considered to have kinetic energy directly related to their temperature & mass.

II. Ideal Gases (we WILL study these a lot!) 5 Assumptions continued: 4. Ideal gas particles are considered to be in continuous random motion. 5. No force of attraction between particles

How can you identify an ideal gas? Gases at high temperature tend to act as ideal gases. Gases at low pressure tend to act as ideal gases. Gases of smaller, non-polar particle units tend to act as ideal gases. Fundamentally, an ideal gas acts as a bunch of small balls randomly bouncing around with no attractions between them.

Real or Ideal Gas Behavior?  Nitrogen Gas at room temperature and 1 atm

Real or Ideal Gas Behavior?  Water vapor at 25 o C and 1 atm

Real or Ideal Gas Behavior?  Helium Gas at room temperature and 1 atm

III. Four Important Characteristics (Ideal Gases) A. Amount (moles) B. Volume (liters) C. Temperature (K) D. Pressure (atm) STP means Standard Temperature & Pressure O o C 1 atm 273 K One mole of an ideal gas at STP = 22.4 L

At STP, 1 mole any gas takes up 22.4 Liters of space.

IV. Characteristic Details A. Amount 1. Indicated in moles (mol) 2. One mole of an ideal gas at STP = 22.4 L B. Volume – the space occupied 1. Indicated in liters (L) 2. Most of the space is empty – particles are far apart 3. One mole of an ideal gas at STP = 22.4 L 4. Easily Changed – Expand or Contract

IV. Characteristic Details (cont.) C. Temperature 1. Indicated in Kelvin (K) 2. A measure of particle speed - independent of mass 3. Related to heat, but NOT heat - heat depends on mass 4. Absolute Zero = O K or -273 o C To Convert o C to K: K = o C + 273

IV. Characteristic Details (cont.) D. Pressure 1. Indicated in Atmosphere’s (atm) 2. A measure of the force particles exert per unit area Pressure = Force / Area - as when the particles hit the walls of a container!

The container on the right experiences a greater number of particle collisions per unit area – the pressure is greater! Greater Pressure

D. Pressure (Cont.) 3. Dalton’s Law Total Pressure = Partial Pressures Added P total = P 1 + P 2 + P 3 … 4. Air Pressure P air = P oxygen + P nitrogen + P other 14.7 psi (lbs per in 2 ) or 1 atm Measured with a barometer – air pushes mercury (Hg) up a tube.

Air Pressure – Related to the weight of a column of air on top of us!

D. Pressure (Cont.) 5. Conversions 1 atm = 760 mm Hg = 14.7 psi DON’T FORGET One mole of an ideal gas at 1 atm and 273 K = 22.4 L But, it must be… at ST….P

If the barometer shows 765 mm Hg, how many Atmospheres is this?

V. Gases in the Laboratory

To get the pressure of just the hydrogen in the flask: You subtract the partial pressure of the water vapor from the total pressure in the flask. (Table on page 859) P H2 gas = P total - P H2O vapor IE: If the pressure in the room is 762 mmHg and the temp. in the room is 21 C, then the partial pressure of just H 2 would be: mm Hg = 743 mm Hg (If you look up Water Vapor Pressure on Pg. 859, it’s 19 mm Hg at 21 C.)