Warm-up. We ll do it at the end today.

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1 3.2 Modelling a Gas

2 Warm-up We ll do it at the end today.

3 Gas Laws Discovered independently and experimentally in various parts of Europe All assume an ideal gas Ideal gases obey all gas laws perfectly Gas is incompressible All molecular interactions are perfectly elastic collisions

4 Gas Laws Boyle s Law For a fixed mass of gas, pressure is inversely proportional to volume Later amended to include constant temperature

5 Gas Laws Boyle s Law

6 Gas Laws Boyle s Law

7 Gas Laws Charles Law For a fixed mass of gas at constant pressure, volume is directly proportional to absolute temperature

8 Gas Laws Charles Law

9 Gas Laws Charles Law

10 Gas Laws Pressure Law (Gay-Lussac s Law) For a fixed volume of gas, temperature and pressure are directly proportional

11 Say what??? Gas Laws Boyle s Law Charles Law Gay-Lussac Law Temp remains constant Pressure remains constant Volume remains constant Increasing volume decreases pressure Increasing heat increases volume Increasing heat increases pressure Decreasing heat decreases volume Decreasing heat decreases pressure Decreasing volume increases pressure

12 Warm-up October History Father of English Lit and author of The Canterbury Tales died Waterway that connected Great Lakes with Atlantic Ocean opened October Revolution began when this leader staged a coup war crimes trials for many Nazi leaders began in this city Air Force pilot became first person to break sound barrier Babe Ruth s home run record was broke by this man this baseball team reversed the curse by winning its first World Series since 1918

constant temperature and pressure, the number of particles is directly proportional to volume We describe the

13 Gas Laws Mols Italian dead guy Count Amadeo Avogadro noticed that all gases seemed to expand by equal amounts when temperatures were raised by the same amount This led him to (correctly) hypothesis that for every gas at constant temperature and pressure, the number of particles is directly proportional to volume We describe the numbers of particles in terms of moles 1 mol = particles in 12 grams of carbon-12 = 6.02 x 1023 atoms = Avogadro s constant

14 Gas Laws Ideal Gas Law (State of an Ideal Gas) We can combine the 3 gas laws we discussed yesterday to get the Ideal Gas Law Hold different quantities constant

15 Thermal Physics Practice The specific heat capacity of a particular block of steel is 450 J kg-1 C -1. When we add 4.2 x106 J of thermal energy to a block of this steel its temperature increases by 12 C. What is the mass of the above block?

16 The following questions are about changing the temperature and phase of a 0.75-kg piece of ice. Its starting temperature is -18 C. 1. The ice is warmed up to 0.0 C without melting. How much heat energy in Joules is needed? 2. The ice at 0 C is now warmed up until it all melts, becoming water at 0 C. How much heat energy in Joules is needed? 3. The water at 0 C is now warmed up until it reaches a temperature of 100 C but does not begin to boil. How much heat energy in Joules is needed?

17 1. The water at 100 C is now warmed up until it all turns into steam at a temperature of 100 C. How much heat energy in Joules is needed? 2. The steam at 100 C is now warmed up until it reaches a temperature of 118 C. How much heat energy in Joules is needed? kilograms of ice at -18 C is warmed up to become steam at 118 C. How much heat energy in Joules is needed?

18 An ideal gas is kept in a fixed volume at a temperature of 25 C and a pressure of 45 kpa. The gas is then heated at constant volume to a temperature of 50 C. Determine its new pressure.

The temperature of the gas is 19.5 C. 1. What force does the gas exert on the cylinder head? 2.

19 The internal volume of a gas cylinder is 4.50 x 10-2 m3. The cylinder head has a diameter of 1.25 cm. An ideal gas is pumped into the cylinder until the pressure becomes 650. kpa. The temperature of the gas is 19.5 C. 1. What force does the gas exert on the cylinder head? 2. Determine how many moles of the gas are there in the cylinder. 3. Determine the number of gas atoms in the cylinder.

20 Warm-up Answers are homonyms To make money; ash container Not working, lazy; a person who is greatly admired Tasty mollusks; biceps, quadriceps Word that follows press or peace; less-edible part of an apple A requirement of necessary thing; to fold or stretch bread dough To bide one s time; measurement of heaviness Period in which a king/queen rules; precipitation To interfere with something that is not your business; a military award Greater in altitude; to employ someone A lodger; line that separates one political territory from another

21 Thermal Physics Review

22 Gas Molecules Diffusion Gas molecules move from high concentration to low Just like heat: transfers from high energy to low until equilibrium Entropy Diffused gases allow you to smell smoke from a distance

23 Gas Molecules Brownian Motion Explains diffusion of gases However, diffusion results in a net mass transfer, Brownian motion does not Molecules and particles of different masses interact and transfer momentum We observe these imbalanced momentum transfers as random movements

Gas Molecules Kinetic Theory of Gases Use statistics to predict movement of gas molecules and to explain properties of gases (pressure and temperature) Theory uses several assumptions to

24 Gas Molecules Kinetic Theory of Gases Use statistics to predict movement of gas molecules and to explain properties of gases (pressure and temperature) Theory uses several assumptions to make math work Basically an Ideal Gas Large number of very small particles evenly mixed throughout a container Only forces acting are perfectly elastic collisions between particles and container

25 Gas Molecules Kinetic Theory Equations Analyzing the forces, velocities, and masses of the gas particles, we can derive two equations Pressure of a gas is determined by the density of the gas,, and the mean velocity of the molecules, c p = ⅓ c2 The average kinetic energy of a gas depends on the number of gas molecules, N, and its temperature, T Ek = 3/2 NkBT

Name: Regents Chemistry: Notes: Unit 8 Gases.

Name: Regents Chemistry: Notes: Unit 8 Gases 1 Name: KEY IDEAS The concept of an ideal gas is a model to explain the behavior of gases. A real gas is most like an ideal gas when the real gas is at low