Chapter 14 Honors Chemistry Gases Chapter 14 Honors Chemistry

Section 1 – The Gas Laws 1. Kinetic Theory The kinetic molecular theory assumes the following concepts about gases are true: Gas particles do not attract or repel each other Gas particles are much smaller than the distance between them Gas particles are in constant, random motion No kinetic energy is lost when gas particles collide with each other or with the walls of their container All gases have the same kinetic energy at a given temperature Actual gases do not obey all these assumptions. But for many, their behavior approximates the behavior assumed by the kinetic theory

2. Boyle’s Law Boyle’s law states that the volume of a fixed amount of gas held at a constant temperature varies inversely with the pressure. P1V1 = P2V2 Where P = pressure and V = volume

3. Charles’s Law As temperature increases, so does the volume of gas when the amount of gas and pressure do not change. Kinetic-molecular theory explains this property At a higher temperature, gas particles move faster, striking each other and the walls of their container more frequently Temperature must be expressed in kelvin. Absolute zero is zero on the Kelvin scale. Charles’s law states that the volume of a given amount of gas is directly proportional to its kelvin temperature at constant pressure.

4. Gay-Lussac’s Law Gay-Lussac’s law states that the pressure of a fixed amount of gas varies directly with the kelvin temperature when the volume remains constant.

End of Section 1

Section 2 – The Combined Gas Law & Avogadro’s Principle The combined gas law states the relationship among pressure, temperature, and volume of a fixed amount of gas.

6. Avogadro's Principle Avogadro’s principle states that equal volumes of gases at the same temperature and pressure contain equal numbers of particles. Therefore, as the number of moles increase so does the volume V1/n1 = V2/n2 Molar volume of a gas is the volume 1 mol occupies at 0.00°C and 1.00 atm of pressure. 0.00°C and 1.00 atm are called standard temperature and pressure (STP). At STP, 1 mol of gas occupies 22.4 L. (22.4 L/mol)

End of Section 2

Section 3 – The Ideal Gas Law Ideal gas law combines, Boyle’s Law, Charles’s Law, Gay- Lussac’s Law, and Avogadro’s Law to describe the relationship between pressure, temperature, volume, and number of moles: For a specific sample of gas, the relationship of pressure, volume, and temperature is always the same. You could say that: Where the constant (k) is based on the amount of gas (number of moles) present, n, therefore: k = nR Where R represents an experimentally determined constant that is referred to as the ideal gas constant.

The Ideal Gas Law (cont.) The Ideal Gas Constant The ideal gas constant is represented by R and is 0.0821 L•atm/mol•K when pressure is in atmospheres. The value of R depends on the units used for pressure Therefore the ideal gas law is: The ideal gas law describes the physical behavior of an ideal gas in terms of pressure, volume, temperature, and amount of moles of gas present.

The Ideal Gas Law (cont.) Real Versus Ideal Gases Real gases deviate most from ideal gases at high pressures and low temperatures. As the amount of space between particles and the speed at which the particles move decrease, the effects of the volume of gas particles and intermolecular forces become increasingly important Condensation occurs to form a liquid Polar molecules have larger attractive forces between particles. Polar gases do not behave as ideal gases. Large nonpolar gas particles occupy more space and deviate more from ideal gases than smaller gas particles.

8. Applying The Ideal Gas Law Molar mass (M) and density (D) can be calculated if the mass of the sample is known Molar mass and the ideal gas law Density and the ideal gas law

End of Section 3

9. Calculations Involving only Volume Section 4 – Gas Stoichiometry 9. Calculations Involving only Volume The gas laws can be applied to calculate the stoichiometry of reactions in which gases are reactants or products. 2H2(g) + O2(g) → 2H2O(g) 2 mol H2 reacts with 1 mol O2 to produce 2 mol water vapor. Avogadro’s principle states that equal volumes of gases at the same temperature and pressure contain equal numbers of particles, therefore, the coefficients also represent relative volumes 2 L of H2 reacts with 1 L of O2 to produce 2 L of water vapor

Calculations Involving only Volume (cont.) You must know the balanced chemical equation for the reaction and the volume of at least one other gas involved in the reaction Coefficients in a balanced equation represent volume ratios for gases. The same as for mol ratios Temperature and pressure conditions are not needed because after mixing each gas is at the same temperature and pressure

10. Calculations Involving Volume and Mass You must know the balanced equation, at least one mass or volume for a reactant or product, and the conditions under which the gas volumes have been measured. Then the ideal gas law can be used along with volume or mole ratios to complete the calculation. Masses given must be found by converting to moles or volumes before being used. Temperature units must be in kelvin.

End of Section 4

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CIM Table 12.4 Unit Cells Table 12.5 Types of Crystalline Solids Figure 12.30 Phase Diagrams

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