Do Now: 1)According to the KMT, what’s true about ideal gasses? 2)When do gasses not behave as ideal gasses? 3)Why use ideal gasses? 1) move in random, straight line 2)elastic collisions 3) So far apart that their volume is negligible 4) No molecular interactions at really low temperature and really high pressure So we can explain the behavior of a sample of gas Topic: The Combined Gas Laws and Avogadro’s Hypothesis

Avogadro’s Hypothesis Equal volumes of gases at same T and P (STP) contain equal # of particles

3 containers – same size, same T, same P Box A He Box B N 2 Box C CH 4 What can you say about # of molecules in each box? # molecules is the same in each box # molecules is the same in each box (1 mole each substance) (1 mole each substance) What can you say about # of atoms in each box? B = 2 x A ; C = 5 x A

Describing Gas Phase System Need 4 variables to completely describe gas-phase system from macroscopic or lab view 1. Pressure 2. Volume 3. Temperature (most be in Kelvin) 4. Amount gas (moles)

Combined Gas Law P 1 V 1 = P 2 V 2 T1T1T1T1 T2T2T2T2 The amt of gas (# of molecules) is constant NOTE: Temp. must be in Kelvin always

Combined Gas Law Given 5 of 6 variables, can identify 6 th If a variable is constant, just ignore it P 1 V 1 = P 2 V 2 P 1 V 1 = P 2 V 2 T 1 T 2 T 1 T 2 If you see STP ST = 273K SP = 1 atm = 760 mmHg = 760 Torr = kPa