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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.
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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.
Gas is made of very tiny atoms or molecules and they move very fast. • Particles move in straight lines.
3. The gas particles are very small (size is negligible) compared to the size of the surrounding
What will happen to the energy if a volley ball is dropped? • Will it lose energy? Can it keep going for ever?
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
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 • 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 > PB A When balloon is filled and tied: PA = PB When balloon deflates: PA < PB A = pressure exerted BY balloon B = pressure exerted ON balloon
A B C 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? Why?
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
N2 CH4 Ar H2 Avogadro’s Hypothesis 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 20oC and 1 atm pressure. Each contains 0.045 mol or 2.69 x 1022 molecules of gas.
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
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 1 atm
K = ºC + 273 Temperature Always use absolute temperature (Kelvin) when working with gases. ºF -459 32 212 ºC -273 0 100 K 0 273 373
STP STP Standard Temperature & Pressure 0°C 1 atm 273 K - OR - 101.325 kPa 760 mm Hg
H2O(g) molecules (water vapor) H2O(l) molecules Evaporation
Boiling vs. Evaporation Boiling point: atmospheric pressure = vapor pressure AIR PRESSURE 15psi 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 kPa at a temperature of 100 oC. This is defined as its normal boiling point: ‘vapor pressure = atmospheric pressure’
