1. Ideal vs. Real Gases No gas is ideal. As the temperature of a gas increases and the pressure on the gas decreases the gas acts more ideally.

2. Real Gases Do Not Behave Ideally CH 4 H2H2 N2N2 CO 2 Ideal gas 2.0 1.0 0 0 200 400 600800 1000 P (atm) PV nRT

3. Equation of State of an Ideal Gas Robert Boyle ( 1662 ) found that at fixed temperature –Pressure and volume of a gas is inversely proportional PV = constantBoyle’s Law J. Charles and Gay-Lussac ( circa 1800 ) found that at fixed pressure –Volume of gas is proportional to change in temperature Volume Temp -273.15 o C All gases extrapolate to zero volume at a temperature corresponding to –273.15 o C (absolute zero). He CH 4 H2OH2O H2H2

4. Copyright © 2007 Pearson Benjamin Cummings. All rights reserved. T 1 T 2 V 1 V 2 = (Pressure is held constant) T 1 T 2 P 1 P 2 = (Volume is held constant)

5. Copyright © 2007 Pearson Benjamin Cummings. All rights reserved. T 1 T 2 V 1 V 2 = (Pressure is held constant) T 1 T 2 P 1 P 2 = (Volume is held constant) Charles Gay-Lussac

6. Kelvin Temperature Scale Kelvin temperature (K) is given by K = o C + 273.15 where K is the temperature in Kelvin, o C is temperature in Celcius Using the ABSOLUTE scale, it is now possible to write Charles’ Law as V / T = constant Charles’ Law Gay-Lussac also showed that at fixed volume P / T = constant Combining Boyle’s law, Charles’ law, and Gay-Lussac’s law, we have P V / T = constant Gay-Lussac Charles