1 Behavior of Gases Ch. 14

2 Why do air bags work? Which would you rather hit the dashboard or an air bag? Why? Which would you rather hit the dashboard or an air bag? Why? –Air bags are filled with air, which is a gas. –When you hit the air bag the gas inside compresses and absorbs some of the energy from the impact of a collision –Dashboard is a solid substance which doesn’t compress so all of the energy of the impact will be transferred to your body

3 What is compressibility? Compressibility – measure of how much the volume of matter decreases under pressure. Compressibility – measure of how much the volume of matter decreases under pressure. –Squeezed into a small volume Gases can be compressed to fill a small volume container Gases can be compressed to fill a small volume container

4 Why can gases be compressed more easily than liquids or solids? Explained by kinetic theory Explained by kinetic theory Gases are easily compressed because of the space between the particles in a gas. Gases are easily compressed because of the space between the particles in a gas. –Volume of particles small compared to overall volume of gas –Distance between particles is large in gases –When gases are pressurized they are force to come closer together i.e. compressed

5 Review: kinetic theory of gases Assumptions Assumptions –Particles move along straight-line paths until they collide with other particles or the walls of their containers –Motion of the particles is constant and random –Particles in a gas move freely since they are not attracted or repelled by each other

6 What affects gas pressure? Four variables used to describe gas Four variables used to describe gas 1.Pressure (P) in kPa 2.Volume (V) in L 3.Temperature (T) in kelvins 4.Number of moles (n) Amount of gas, volume, and temperature are factors that affect gas pressure Amount of gas, volume, and temperature are factors that affect gas pressure

7 Amount of gas If you  amount of gas you  the number of particles as a result If you  amount of gas you  the number of particles as a result –Collisions  and the pressure  Opposite also true  amount of gas pressure  Opposite also true  amount of gas pressure  If volume and temperature are constant if you double amount of gas you will double the pressure If volume and temperature are constant if you double amount of gas you will double the pressure

8 Did you ever open a can of new tennis balls? What sound do you hear? Why? What sound do you hear? Why? –Whoosh –The can is packaged under a vacuum –  pressure in can is less than outside –When can is open air from the outside rushes in and causes the noise What do you think would happen is the pressure in the can was greater than the outside pressure? What do you think would happen is the pressure in the can was greater than the outside pressure?

9 How does a spray paint can work? In this case pressure inside of can is greater than outside In this case pressure inside of can is greater than outside Pushing spray button creates an opening between the inside of the can and the air outside Pushing spray button creates an opening between the inside of the can and the air outside –Gas flows out of can and this movement propels or forces the paint out of the can

10 How does volume affect pressure? Another way to  pressure is to  volume Another way to  pressure is to  volume More gas is compress greater the pressure More gas is compress greater the pressure If temperature and amount of gas is constant If temperature and amount of gas is constant –If volume  from 1 L to 0.5 L the pressure will double Opposite also true Opposite also true  volume  pressure  volume  pressure –Inversely proportional

11 How does temperature affect pressure? As a gas is heated, the temperature increases and the average kinetic energy of the particles in the gas increases As a gas is heated, the temperature increases and the average kinetic energy of the particles in the gas increases –Faster moving particles impact the wall of the container with more energy –  pressure increases –Directly proportional If volume and amount If volume and amount of gas are constant –As Temperature  pressure 

12 Boyle’s Law By squeezing the balloon, you reduce the volume or space the gas particles can occupy and as a result the pressure increases. By squeezing the balloon, you reduce the volume or space the gas particles can occupy and as a result the pressure increases. –Why? –Because the particles are closer together and bump into each other and the walls of the balloon more.  volume of gas  pressure if temperature and number of particles are constant  volume of gas  pressure if temperature and number of particles are constant This relationship between Pressure and Volume is called Boyle’s Law This relationship between Pressure and Volume is called Boyle’s Law

13 Boyle’s Law (Cont.) Boyle’s Law - The volume of a fixed amount of gas varies inversely with the pressure of the gas. Boyle’s Law - The volume of a fixed amount of gas varies inversely with the pressure of the gas. –As the volume decreases the pressure increase –As the volume increases the pressure decreases –Where P stands for pressure and V stands for volume (initial state 1 and final state 2) OR

14 Calculations with Boyle’s Law A 2.0 liter container of nitrogen had a pressure of 3.2 atm. What volume would be necessary to decrease the pressure to 1.0 atm? A 2.0 liter container of nitrogen had a pressure of 3.2 atm. What volume would be necessary to decrease the pressure to 1.0 atm? Write down the information given in the problem: Write down the information given in the problem: Information: P 1 =3.2 atm P 1 =3.2 atm V 1 =2.0 liter V 1 =2.0 liter P 2 = 1.0 atm P 2 = 1.0 atm V 2 = ? V 2 = ? Rewrite it

15 Answer:

16 Relationship between Temperature and Volume of Gases Imagine you have a balloon filled with gas again, but this time you heat the balloon. Imagine you have a balloon filled with gas again, but this time you heat the balloon. What do you think will happen? What do you think will happen? –As the gas is heated it is absorbing more heat energy –This makes the particles move faster, which results in the particles moving farther away from one another The volume increases. The volume increases. This relationship is called Charles’s Law This relationship is called Charles’s Law

17 Charles’s Law Charles’s Law - The volume of a fixed amount of gas varies directly with the temperature of the gas. Charles’s Law - The volume of a fixed amount of gas varies directly with the temperature of the gas. –If the temperature of the gas increases so does the volume. –Where T is Temperature measured in Kelvin and V is volume of initial state 1 and final state 2 or

18 Temperature in Kelvin In order to make calculations using Charles’ Law the Temperature has to have units of Kelvin (K). In order to make calculations using Charles’ Law the Temperature has to have units of Kelvin (K). K = ° C K = ° C So using the above equation temperatures in ° C can be convert to K by adding 273 So using the above equation temperatures in ° C can be convert to K by adding 273

19 Calculating with Charles’s Law A sample of Nitrogen occupies a volume of 250 mL at 25 °C. What volume will it occupy at 95 °C? A sample of Nitrogen occupies a volume of 250 mL at 25 °C. What volume will it occupy at 95 °C? Write down the given information: Write down the given information: Information: V 1 = 250 mL V 1 = 250 mL T 1 = 25 °C +273 = 298 K T 1 = 25 °C +273 = 298 K T 2 = 95 °C +273 = 368 K T 2 = 95 °C +273 = 368 K V 2 = ? V 2 = ? Rewrite

20 Answer:

21 How are pressure and temperature related? What happens to your tire pressure on a hot day? What happens to your tire pressure on a hot day? –It goes up As the temperature of an enclosed gas increases, the pressure increases, if the volume is constant As the temperature of an enclosed gas increases, the pressure increases, if the volume is constant This relationship is known as the Gay- Lussac’s Law This relationship is known as the Gay- Lussac’s Law

22 Gay-Lussac’s Law Gay-Lussac’s Law – states that the pressure of a gas is directly proportional to the Kelvin temperature if the volume remains constant. Gay-Lussac’s Law – states that the pressure of a gas is directly proportional to the Kelvin temperature if the volume remains constant. –If temperature increases Pressure increases –Temperature and pressure are directly proportional –Where T is for temperature in Kelvin and P is for pressure or

23 Calculating with Gay-Lussac’s Law A gas has a pressure 103 kPa at a temperature of 25 °C. If the can is thrown onto a fire, what will the pressure be when the temperature reaches 928 °C? A gas has a pressure 103 kPa at a temperature of 25 °C. If the can is thrown onto a fire, what will the pressure be when the temperature reaches 928 °C? Write down the give information Write down the give information Information Information P 1 = 103 kPa P 1 = 103 kPa T 1 = 25 °C = 298 K T 1 = 25 °C = 298 K T 2 = 928 °C = 1201 K T 2 = 928 °C = 1201 K P 2 = ? P 2 = ? rewrite

24 Answer

25 Combined Gas Law When you combined Boyle, Charles, and Gay- Lussac’s Law When you combined Boyle, Charles, and Gay- Lussac’s Law Get combined gas law Get combined gas law Combined gas law allows you to do calculations for situations in which only the amount of gas is constant Combined gas law allows you to do calculations for situations in which only the amount of gas is constant

26 Combined gas law problem The volume of a gas-filled balloon is 30.0 L at 313 K and 153 kPa pressure. What would the volume be at standard temperature and pressure (STP)? The volume of a gas-filled balloon is 30.0 L at 313 K and 153 kPa pressure. What would the volume be at standard temperature and pressure (STP)? Information Information V 1 =30.0 L V 1 =30.0 L T 1 =313 K T 1 =313 K P 1 = 153 kPa P 1 = 153 kPa T 2 = 273 K T 2 = 273 K P 2 = kPa P 2 = kPa V 2 = ? V 2 = ? rewrite

27 Answer

28 Ideal Gas Law To calculate the number of moles of contained gas requires an expression that contains the variable n. To calculate the number of moles of contained gas requires an expression that contains the variable n. PV = nRT PV = nRT Where P is pressure, V is volume, T is Temperature, n is moles, and R is the ideal gas constant Where P is pressure, V is volume, T is Temperature, n is moles, and R is the ideal gas constant R = 8.31 L kPa/K mole R = 8.31 L kPa/K mole

29 Dalton’s Law Partial pressure – the contribution each gas in a mixture of gases makes to the total pressure Partial pressure – the contribution each gas in a mixture of gases makes to the total pressure In a mixture of gases, the total pressure is the sum of the partial pressures of the gases In a mixture of gases, the total pressure is the sum of the partial pressures of the gases Dalton’s law of partial pressures states that at constant volume and temperature, the total pressure exerted by a mixture of gases is equal to the sum of the partial pressures of the component gases. Dalton’s law of partial pressures states that at constant volume and temperature, the total pressure exerted by a mixture of gases is equal to the sum of the partial pressures of the component gases.

30 Diffusion and Effusion Diffusion – tendency of molecules to move toward areas of lower concentration until the concentration is uniform throughout Diffusion – tendency of molecules to move toward areas of lower concentration until the concentration is uniform throughout Diffusion Effusion – gas escapes through a tiny hole in its container Effusion – gas escapes through a tiny hole in its container Gases of lower molar mass diffuse and effuse faster than gases of higher molar mass. Gases of lower molar mass diffuse and effuse faster than gases of higher molar mass.