Kinetic molecular theory What is the difference between

Kinetic molecular theory What is the difference between kinetic and potential energy?

Basic gas laws IDEAL GAS LAWS What are the characteristics of an ideal student?

Observe the movement of gas particles. Comment on their movement. Write your observation.

1. Gas is made of very tiny atoms or molecules and they move very fast. 2. Particles move in straight lines.

3. The gas particles are very small (size is negligible) compared to the size of the surrounding

4. Gas particles do not have any attraction between them.

• What will happen to the energy if a volley ball is dropped? • Will it lose energy? Can it keep going for ever?

5. When gas particles collide energy or speed is not lost.

This is what happens not in REAL situation but in an IDEAL one • That is why we call these rules ‘ideal’ gas laws. • In real situations, it will vary.

Real Gases • Particles in a REAL gas… – have their own volume – attract each other When do students behave as ‘ideal’ students? (under what circumstances? )

• Gas behavior is most ideal… – at low pressures – at high temperatures – in nonpolar atoms/molecules

Relation between temperature and speed of particles.

Speed of particle movement and temperature are related.

When particles move fast, temperature increases.

When particles move slowly, temperature decreases.

What is pressure? A quick write.

Collision of particles on the walls of the container causes pressure.

Speed of particles temperature

What is the impact on gas molecules if the temperature is increased? Will the pressure increase or decrease? This is a closed system.

When temperature increases the speed of the particles and the number of collisions increase. There will be more pressure in a closed system.

Higher temperature decreases pressure in an open environment because gas expands and particles are separated.

Characteristics of Gases expand to fill any container. – random motion, no attraction Gases have very low densities. – no volume = lots of empty space

Characteristics of Gases • Gases can be compressed. – no volume = lots of empty space • Gases undergo diffusion

Pressure and Balloons B When balloon is being filled: PA > P B A When balloon is filled and tied: PA = P B When balloon deflates: PA < P B A = pressure exerted BY balloon B = pressure exerted ON balloon

Balloon Riddle When the balloons are untied, will the large balloon (A) inflate the small balloon (B); will they end up the same size or will the small balloon inflate the large balloon? A B Why? C

Avagadro's Hypothesis Equal volumes of gases at the same T and P have the same number of molecules. V = n(RT/P) = kn This means, for example, that number of moles goes up as volume goes up. 1 mole = 6. 022 x 1023

One mole of any gas at STP occupies 22. 4 liters

Avogadro’s Hypothesis N 2 H 2 Ar CH 4 At the same temperature and pressure, equal volumes of different gases contain the same number of molecules. Each balloon holds 1. 0 L of gas at 20 o. C and 1 atm pressure. Each contains 0. 045 mol or 2. 69 x 1022 molecules of gas.

If you double the number of molecules 1 atm

If you double the number of molecules… You double the pressure. 2 atm

As you remove molecules from a container the how will it affect pressure? 4 atm

As you remove molecules from a container the pressure decreases. 4 atm

1 atm • As you remove molecules from a container the pressure decreases • Until the pressure inside equals the pressure outside • Molecules naturally move from high to low pressure

Temperature Always use absolute temperature (Kelvin) when working with gases. ºF -459 ºC -273 K 0 32 212 0 100 273 373 K = ºC + 273

STP Standard Temperature & Pressure 273 K 0°C 1 atm - OR - 101. 325 k. Pa 760 mm Hg

Vapor pressure

Evaporation H 2 O(g) molecules (water vapor) H 2 O(l) molecules

Boiling vs. Evaporation Boiling point: atmospheric pressure = vapor pressure AIR PRESSURE 15 psi VAPOR PRESSURE 15 psi Evaporation: molecules go from liquid to gas phase gas liquid

Boiling Point on Mt. Everest Water exerts a vapor pressure of 101. 3 k. Pa at a temperature of 100 o. C. This is defined as its normal boiling point: ‘vapor pressure = atmospheric pressure’

Behavior of a liquid in a closed container