1. The Gas Laws First we will classify each law, then we will work with them

2. But before we discuss the laws, let’s define the abbreviations that will be used P T V n k  Pressure exerted by the gas  Temperature in kelvins of the gas  Total volume occupied by the gas  Number of moles of the gas  A constant

3. Back to the laws What did we see during the lab? What did we see during the lab? As volume decreases, the pressure increases, if temperature and the number of molecules remain the same. As volume decreases, the pressure increases, if temperature and the number of molecules remain the same. So, when we multiply pressure of a gas times the volume, the result is a constant. So, when we multiply pressure of a gas times the volume, the result is a constant. PV=k PV=k Therefore, P 1 V 1 =P 2 V 2 Therefore, P 1 V 1 =P 2 V 2 This is Boyle’s Law This is Boyle’s Law

4. Temperature and Volume Relationships As temperature increases, the volume increases, if pressure and the number of molecules remain the same. As temperature increases, the volume increases, if pressure and the number of molecules remain the same. So, when we divide volume of a gas by the temperature, the result is a constant. So, when we divide volume of a gas by the temperature, the result is a constant. V/T=k V/T=k Therefore, V 1 /T 1 = V 2 /T 2 Therefore, V 1 /T 1 = V 2 /T 2 This is Charles’s Law This is Charles’s Law

5. Temperature and Pressure Relationships As temperature increases, the pressure increases, if volume and the number of molecules remain the same. As temperature increases, the pressure increases, if volume and the number of molecules remain the same. So, when we divide pressure of a gas by the temperature, the result is a constant. So, when we divide pressure of a gas by the temperature, the result is a constant. P/T=k P/T=k Therefore, P 1 /T 1 = P 2 /T 2 Therefore, P 1 /T 1 = P 2 /T 2 This is Gay-Lussac’s Law This is Gay-Lussac’s Law

6. Another law from Gay-Lussac Gay-Lussac’s law of combining volumes Gay-Lussac’s law of combining volumes States that the volume of gases involved in a chemical change can be represented by the ratio of small whole numbers. States that the volume of gases involved in a chemical change can be represented by the ratio of small whole numbers. In other words, the coefficients in a chemical equation that involve gases that are at the same temperature and pressure can be equal to liters of each. In other words, the coefficients in a chemical equation that involve gases that are at the same temperature and pressure can be equal to liters of each.

7. Examples 3H 2 (g) + N 2 (g)  2 NH 3 This could mean that 3 liters of hydrogen combine with 1 liter of nitrogen to make 2 liters of ammonia 2H 2 O (l) + electricity  2H 2 (g) + O 2 (g) In this reaction, the volume of hydrogen will be twice that of oxygen produced.

8. Volume and mole relationships Remember this mole day song. “Equal volume of gases at the same temp and pressure have the same number of molecules. Amadeo Avogadro, that’s his hypothesis.”

9. What does this mean? It means that V/n = k, as long as the pressure and temperature remain the same. It means that V/n = k, as long as the pressure and temperature remain the same. The set of conditions that has been defined to measure volumes of gases is 0  C and 1 atm. This is STP, standard temperature and pressure The set of conditions that has been defined to measure volumes of gases is 0  C and 1 atm. This is STP, standard temperature and pressure When these conditions are met, it works out that 1 mol of a gas occupies 22.4 L. When these conditions are met, it works out that 1 mol of a gas occupies 22.4 L. Does that number look familiar? Does that number look familiar?

10. Dalton’s Contribution to Gas Laws Dalton’s law of partial pressure Dalton’s law of partial pressure Partial Pressure – the pressure of each gas in a mixture Partial Pressure – the pressure of each gas in a mixture States that the total pressure of a mixture of gases is equal to the sum of the partial pressures of the component gases. States that the total pressure of a mixture of gases is equal to the sum of the partial pressures of the component gases. P total = P A + P B + P C, P total = P A + P B + P C, Where P total is the total pressure and P A, P B, P C are the partial pressures of each gas Where P total is the total pressure and P A, P B, P C are the partial pressures of each gas

11. So, those are the basic gas laws Boyle’s Law P 1 V 1 =P 2 V 2 Charles’s Law V 1 /T 1 = V 2 /T 2 Gay-Lussac’s Law P 1 /T 1 = P 2 /T 2 Avogadro’s Law V 1 /n 1 = V 2 /n 2 Dalton’s law of partial pressure P total = P A + P B + P C

12. Now, let’s take a look at some problems We will look at page 432, questions 5-9. As we complete them, I will use the following chart and big Vs to help solve the problems. Hopefully it will help. We will look at page 432, questions 5-9. As we complete them, I will use the following chart and big Vs to help solve the problems. Hopefully it will help. PTV 1 2 Notice: alphabetical order and T in Kelvin

13. Homework Page 446: 36, 39, 40, 41, 42, 45, 47, 50, 51. Page 446: 36, 39, 40, 41, 42, 45, 47, 50, 51.