Chapter 12, Standard 4: The kinetic molecular theory describes the motion of atoms and molecules and explains the proper

1. Chapter 12, Standard 4: The kinetic molecular theory describes the motion of atoms and molecules and explains the properties of gases. Three states of matter are: solid; liquid; gas. Characteristics or properties of state each state include: a) Solids - have fixed shape - have fixed volume - atoms or molecules can only vibrate b) Liquids – have no fixed shape (takes up shape of container) - have fixed volume - atoms or molecules can flow c) Gases - have no fixed shape - have no fixed volume (occupies the volume of the container) - atoms or molecules move at random in straight lines. - atoms or molecules have no force of attraction between them. - have low density - are highly compressible

2. GAS PRESSURE standard 4a: Students know the random motion of molecules and their collisions with a surface create the observable pressure on that surface. In a container, gas particles are on continuous motion. They constantly are hitting the walls of the container. This hitting causes gas pressure. Pressure (P) is defined as force (F) per unit area (A). p = Diffusion: When two or more liquids, or gases are placed in contact with each other, since their atoms or molecules are continuously moving, they hit each other and move about trying to occupy the whole container. (mixing of liquids or gases). This is called diffusion.

3. The Gas laws: standard 4c: Students know how to apply the gas laws to study relations between the pressure, temperature, and volume of any amount of an ideal gas or any mixture of ideal gases. These are laws that predict the behavior of gases when subjected to given conditions of temperature, pressure, volume, or when their number of molecules (mole) or mass change. There are 4 gas laws Boyle’s law Charles’s law Avogadro’s law Gay-Lussac’s law

4. 1) BOYLE’S law It states that for a given mass of gas, its volume (V) is inversely proportional to its pressure (P) when temperature (T) remains constant. That is, if gas is in a sealed container and the volume of the container made bigger, then the pressure of the gas will decrease. Mathematically, this law is written as P a 1 or P.V = Cnt (where Cnt is a constant) V Or it can also be written as P1.V1 = P2.V2

5. Example If 2.5L of a gas at 110.0 kPa is expanded to 4.0L at constant temperature, what will happen to the pressure? What will be the new value of the pressure? Solution Data: V1= 2.5 L, V2= 4.0 L, P1 =110.0kPa, P2 = ? From Boyle’s law P1.V1 = P2.V2 Therefore 110.0kPa x 2.5 L = P2 x 4.0 L So P2 = 110.0kPa x 2.5 L = 69.0kPa 4.0 L

6. Practice If 650mL hydrogen is stored in a cylinder with a movable piston at 225kPa and the pressure increased to 545kPa at constant temperature, what will be the new volume?

7. Standard 4e: Students know how to convert between the Celsius and Kelvin temperature scales.  Celsius and Kelvin scales

8. Practice questions 1. How do the units (intervals) in the Kelvin scale and the Celsius scale compare? 2. What is the freezing point of water in Kelvin? 3. What is 20°C in Kelvin? 4. What is 100°C in Kelvin? 5. What is 0 K in Celsius? 6. What is 100 K in Celsius?

9. 2) Charles’s law It states that for a given mass of gas at constant pressure (P), its volume (V) is directly proportional to its temperature (T). That is, at a fixed pressure, when the temperature of a gas in a sealed container increases, its volume will also increased. Mathematically this law is written as V a T or V = Cnt (where Cnt is a constant) T Or V1 = V2 or V1T2 = V2T1 T1 T2

10. Example A balloon with a volume of 15.5 L is inflated in a room at 20.0°C and then taken outside where the temperature is 7.0°C. What will be the new volume of the balloon if the pressure remained constant? Solution Data: V1 = 15.5L, V2 = ? T1 = (20.0 + 273)K = 293K T2 = (7.0 + 273)K = 280K From Charles’s law V1T2 =V2T1 So 15.5 L x 280K = V2 x 293K Therefore V2 = 15.5L x 280K = 14.8 L 293K

11. Application 1) The volume of a syringe is 15.0 mL at 23.5°C. What will the volume of the gas be at 72.5°C if the pressure is held constant? 2) A gas takes up 14.8 liters at 24°C. What temperature in kelvin is required to obtain a volume of 25.0 liters at constant pressure?

12. Gay-Lussac’s law It states that for a given mass of gas at constant volume (V), its pressure (P) is directly proportional to its temperature (T). That is, if a given amount of gas is put in a sealed container, when its temperature is increased by heating it, its pressure will also increase if the volume remains fixed. Mathematically, this law is written as P a T or P = Ct (where Ct is a constant) T Or P1 = P2 or P1.T2 = P2.T1 T1 T2

13. practice The pressure in the tire of a car is 101 kPa at 10.0?C, what will be the pressure of the tire at 45.0?C? Solution Data: P1 = 101 kPa, P2 = ? T1 = (10.0 + 273)K = 283K T2 = (45.0 + 273)K = 318K From gay-Lussac’s law, P1T2 = P2T1 So 101kPa x 318K = P2 x 283K Therefore P2 = 101kPa x 318K = 113kPa 283K

14. practice The pressure in a bottle of soda pop is 505kPa at 20°C, what is the new pressure if someone warms the sealed bottle to 65.0°C?

15. Standard 4d: Students know the values and meanings of standard temperature and pressure (STP).  Standard temperature and pressure, (STP) Value of STP: Standard temperature is 0°C or 273K Standard pressure is 760mmHg or 1 atmosphere (atm) Meaning of standard temperature and pressure 0°C or 273K is the temperature at which water freezes or ice melt. 760mmHg or 1 atm is the atmospheric pressure at sea level. These two values were chosen by scientist as standards.

16. Avogadro’s law It states that at constant pressure and temperature, the volume of a gas is directly proportional to the number of molecules (moles) of gas in the container. That is, if more gas (air) is pumped into a container at fixed temperature and pressure, its volume will increase. Mathematically, this law is written as V = k.n or V1/n1 = V2/n2 (where k is a constant and n is the number of moles of the gas) At STP, 1 mole of any gas will occupy 22.41L