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Objectives. To understand the ideal gas law and use it in calculations To understand the relationship between the partial and total pressure of a gas mixture To do calculations involving Dalton’s law of partial pressures To understand the molar volume of an ideal gas
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Objectives • To understand the ideal gas law and use it in calculations • To understand the relationship between the partial and total pressure of a gas mixture • To do calculations involving Dalton’s law of partial pressures • To understand the molar volume of an ideal gas • To learn the definition of STP • To do stoichiometry calculations using the ideal gas law
A. The Ideal Gas Law • Boyle’s Law V = k(at constant T and n) P • Charles’s Law V = bT (at constant P and n) • Avogadro’s Law V = an (at constant T and P) We can combine these equations to get
A. The Ideal Gas Law • Rearranging the equation gives the ideal gas law: • PV = nRT • R is a constant = 0.08206 L atm • mol K • Note the units that are used with this constant
The Combined Gas Law Ideal Gas Law: PV = nRT P1V1 = nRT1or P1V1/T1 = nR P2V2 = nRT2or P2V2/T2 = nR Combined Gas Law: P1V1/T1 = P2V2/T2 (for a constant number of moles)
B. Dalton’s Law of Partial Pressures • What value do we measure for the pressure of a gas as we mix different gases in a container? Dalton’s law of partial pressures • For a mixtures of gases in a container, the total pressure exerted is the sum of the partial pressures of the gases present. • Ptotal = P1 + P2 + P3 + …….
B. Dalton’s Law of Partial Pressures • The pressure of the gas is affected by the number of particles. • The pressure is independent of the nature of the particles.
B. Dalton’s Law of Partial Pressures Two crucial things we learn from this are: • The volume of the individual particles is not very important • The forces among the particles must not be very important
B. Dalton’s Law of Partial Pressures Collecting a gas over water • Total pressure is the pressure of the gas + the vapor pressure of the water. Collecting Hydrogen
B. Dalton’s Law of Partial Pressures Collecting a gas over water • How can we find the pressure of the gas collected alone?
C. Gas Stoichiometry Molar Volume • Standard temperature and pressure (STP) • 0oC and 1 atm • For one mole of a gas at STP, what is the volume? • Molar volume of an ideal gas at STP = 22.4 L