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The Gas Laws: Classification, Concepts, and Problem Solving

Learn about the fundamental gas laws including Boyle's Law, Charles's Law, Gay-Lussac's Law, Avogadro's Law, and Dalton's Law. Understand the relationships between pressure, temperature, volume, and moles of gases. Solve practice problems to reinforce your knowledge.

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The Gas Laws: Classification, Concepts, and Problem Solving

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

  2. 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 But before we discuss the laws, let’s define the abbreviations that will be used

  3. Back to the laws • What did we see during the lab? • 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. • PV=k • Therefore, P1V1=P2V2 • 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. • So, when we divide volume of a gas by the temperature, the result is a constant. • V/T=k • Therefore, V1/T1= V2/T2 • 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. • So, when we divide pressure of a gas by the temperature, the result is a constant. • P/T=k • Therefore, P1/T1= P2/T2 • This is Gay-Lussac’s Law

  6. Another law from Gay-Lussac • 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. • 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 3H2 (g) + N2 (g)  2 NH3 This could mean that 3 liters of hydrogen combine with 1 liter of nitrogen to make 2 liters of ammonia 2H2O (l) + electricity  2H2 (g) + O2 (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. • 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. • Does that number look familiar?

  10. Dalton’s Contribution to Gas Laws • Dalton’s law of partial pressure • 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. • Ptotal = PA + PB + PC, • Where Ptotal is the total pressure and PA, PB, PC are the partial pressures of each gas

  11. So, those are the basic gas laws

  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. Notice: alphabetical order and T in Kelvin

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

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