Gases and Gas Laws Past Paper PDF

Gases and gases laws 24/10/2024 Gases and gases laws 24/10/2024 Gases and gases laws Using Gas Laws to Determine a Balanced Equation PROBLEM: The piston-cylinder is depicted before and after a gaseous rea...

Gases and gases laws 24/10/2024 Gases and gases laws 24/10/2024 Gases and gases laws Using Gas Laws to Determine a Balanced Equation PROBLEM: The piston-cylinder is depicted before and after a gaseous reaction that is carried out at constant pressure. The temperature is 150 K before the reaction and 300 K after the reaction. (Assume the cylinder is insulated.) Which of the following balanced equations describes the reaction? (1) A2 (g) + B2 (g) → 2AB (g) (2) 2AB (g) + B2 (g) → 2AB2 (g) (3) A (g) + B2 (g) → AB2 (g) (4) 2AB2 (g) → A2 (g) + 2B2 (g) 24/10/2024 Gases and gases laws PLAN: We are told that P is constant for this system, and the depiction shows that V does not change either. Since T changes, the volume could not remain the same unless the amount of gas in the system also changes. n2 T1 150 K SOLUTION: n1T1 = n2T2 = = =½ n1 T2 300 K Since T doubles, the total number of moles of gas must be halve – i.e., the moles of product must be half the moles of reactant. This relationship is shown by equation (3). A (g) + B2 (g) → AB2 (g) 24/10/2024 Gases and gases laws The ideal gas law and gas density The density of a gas is - Directly proportional to its molar mass and - Inversely proportional to its temperature. - Directly proportional to the pressure. m m density = and moles = V M m PV = RT M m M xP =d= V RT 24/10/2024 Gases and gases laws 24/10/2024 Gases and gases laws Molar mass from the ideal gas law m PV mRT n= = M= M RT PV Where: m= mass in gm M= atomic mass in gm/mol (from periodic table) 24/10/2024 Gases and gases laws 24/10/2024 Gases and gases laws Mixtures of gases Gases mix homogeneously in any proportions. Each gas in a mixture behaves as if it were the only gas present. The pressure exerted by each gas in a mixture is called its partial pressure. Dalton’s Law of partial pressures states that “The total pressure in a mixture is the sum of the partial pressures of the component gases”. The partial pressure of a gas is proportional to its mole fraction: PA = ΧA x Ptotal nA XA = ntotal 24/10/2024 Gases and gases laws 24/10/2024 Gases and gases laws Familiar applications of the gas laws 24/10/2024