STAAR Chemistry Review Topic: Gas Properties TEKS 9 – The student understands the principles of ideal gas behavior, kinetic molecular theory, and the conditions that influence the behavior of gases. 9A-C

Student Expectation 9A – describe and calculate the relations between volume, pressure, number of moles, and temperature for an ideal gas as described by Boyle’s law, Charles’ law, Avogadro’s law, Dalton’s law of partial pressures, and the ideal gas law.

INDEX CARD TIME! TITLE: Gas Properties and STP FRONT: List the four physical properties that are used to describe gas behavior and their symbols (P, V, T, and n) BACK: Give the symbol and unit of measure used in chemistry to quantify each property. For temperature and pressure, give the value used in defining standard conditions. Give the numerical value of the volume occupied by a mole of gas at STP

Mini-Review A sample of gas can be described using the properties of pressure (P), volume (V), temperature (T), and number of moles (n) Historically, scientists investigated how various pairs of these properties were related to each other, while keeping the other properties constant. Standard conditions when working with gases are P = 1 atmosphere and T = 273 K. At these conditions, 1 mole of gas occupies a volume of 22.4 L

INDEX CARD TIME! TITLE: Dalton’s Law of Partial Pressures FRONT: Give the equation that describes this law of ideal gas behavior for gas mixtures BACK: Describe in your own words the meaning of the law, and give a numerical example of its use

Mini-Review John Dalton found that in a mixture of ideal gases each gas exerts its own pressure upon the walls of the container. The pressure exerted by each gas in a mixture is called its partial pressure. Dalton’s law means that the total pressure exerted by all of the gases in the mixture can be found by simply adding together their partial pressures : P T = P 1 + P 2 + P

INDEX CARD TIME! TITLE: Individual Gas Laws FRONT: Put the title on the front of this card BACK: Make a table with the following headings: Gas Law, Equation, and Description Summarize the 4 individual gas laws on this table

Mini-Review Robert Boyle found that when he increased the pressure on a sample of gas, while keeping the temperature constant, the volume of the gas decreased, and that the product of the pressure and volume was a constant. This kind of relationship is called an inverse relationship. Boyle’s results can be expressed as P 1 V 1 = P 2 V 2

Mini-Review Jacques Charles found that if he increased the temperature of a sample of gas (while keeping the pressure constant), the gas occupied a greater volume (it expanded). He found that the volume increased by the same amount for a given increase in temperature. That is, volume and temperature were directly proportional to each other We can express this relationship as follows:

Mini-Review Amedeo Avogadro hypothesized that equal volumes of gas contained equal numbers of tiny particles he called “molecules” This is the same thing as saying that equal volumes contain equal numbers of moles of gas The gas law named in his honor states that volume and number of moles are directly proportional to each other:

INDEX CARD TIME! TITLE: The Ideal Gas Law FRONT: Give the equation that describes this law of ideal gas behavior BACK: Describe in your own words the meaning of the law. Show the values and units of measure for the ideal gas constant (R) and explain why there are several different values for this constant. Give an example problem using the Ideal Gas Law

Mini-Review The ideal gas law combines the findings of the individual gas laws. It states that the product of pressure and volume is directly proportional to the product of number of moles and temperature. We can make this into an equation if we introduce a constant of proportionality called the ideal gas constant, R, whose value depends on the units of measure used for the gas properties: PV = nRT

Student Expectation 9B – perform stoichiometric calculations, including determination of mass and volume relationships between reactants and products for reactions involving gases.

INDEX CARD TIME! TITLE: Gas Stoichiometry FRONT: Summarize the relationships among mass, molar volume at STP, and number of moles for a gaseous reactant or product BACK: Give examples of problems involving the use of the volume of a mole of gas at STP

Mini-Review You can use the relationships between number of moles, molar mass, and molar volume at STP to find any of the related quantities For example: Starting with number of moles of a gas: To find mass of gas: multiply moles by molar mass (g/mol) To find volume of gas: multiply moles by molar volume at STP (22.4 L/mol)

Mini-Review: Stoichiometry Use the train track method to start with what you know, then multiply by factors than convert from the units given to obtain the answer in the units you want. The balanced chemical equation will tell you the relationships between the number of moles of reactants and products

Mini-Review: Stoichiometry Here’s an example: Calculate the volume of oxygen (at STP) produced by the decomposition of 56 g of KClO 3 (molar mass = g): 2KClO 3 (s)  2KCl(s) + 3O 2 (g) 56 g KClO 3 x 1 mol KClO 3 x _3 mol O 2 x 22.4 L O g KClO 3 2 mol KClO 3 1 mol O 2 = 15 L O 2

Student Expectation 9C – describe the postulates of kinetic molecular theory

INDEX CARD TIME! TITLE: Postulates of the Kinetic Molecular Theory FRONT: List the five postulates of the kinetic molecular theory that apply to ideal gases. BACK: Give examples of gases that can be expected to behave closest to the postulates. Give examples of the conditions under which these postulates are likely to be met for real gases.

Mini-Review The kinetic molecular theory is a simplified model that can explain the behavior of ideal gases, so it has limitations when applied to real gases. The kinetic molecular theory implies that matter is made up of extremely tiny particles that are constantly moving (except at 0 K!) Since they are so tiny, the volume occupied by the gas molecules or atoms can be ignored when compared to the volume of the sample

Mini-Review Collisions between gas molecules or between molecules and the container walls don’t result in any energy changes; they act like tiny, hard billiard balls Since any forces of attraction or repulsion between ideal gas molecules are neglected, they can’t clump together. This means that no matter how cold it gets, a truly ideal gas can never condense into a liquid! The absolute temperature of a sample of an ideal gas is a measure of the molecules’ average kinetic energy