chemistry 103 lecture 19. general course structure - week 5 atoms ---> compounds ---> chemical...
TRANSCRIPT
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Chemistry 103
Lecture 19
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General Course structure - WEEK 5
Atoms ---> Compounds ---> Chemical Reactions
GAS LAWS
SOLUTIONS
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Outline
I. GAS LAWS continued ….. - Ideal/Combined Gas Law - Stoichiometry - modified gas expression - Dalton’s law of Partial Pressure
II. SOLUTIONS - INTRODUCTION
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Important Simple Gas Relationships Boyles Law P1V1 = P2V2 (T fixed)
Charles Law V1/T1 = V2/T2 (P fixed)
Gay-Lussacs P1/T1 = P2/T2 (V fixed) Avogadros Law V1/n1 = V2/n2 (T&P fixed)
STP - Standard Temperature and Pressure (Gases)
T = 273 K (0 oC) and P = 1 atm (760 mmHg)
1 mole of a gas at STP = 22.4L
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Combined Gas Laws
Relates the changes in pressure, volume and temperature, and quantity change of a gas
PV = constant
nT
Useful form of the expression:
P1V1 = P2V2
n1T1 n2T2
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Ideal Gas Law
Let’s now solve for the constant:
PV/nT = constant = R = 0.0821atm L
mol K
IDEAL GAS LAW : PV=nRT
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Gas Laws
A balloon contains 2.5L of Helium gas when the inside temperature is 25oC (approx 77oF). Assuming constant pressure, what is the volume of the balloon when you walk outside on a cold winter day with a temperature of
-20oC ( -4oF).
A. 48
B. 2.9
C.2.1
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Gas Laws
A spray can is empty except for the propellant gas, which exerts a pressure of 1.2 atm at 24oC. If the can is thrown into a fire (485oC), what will be the pressure (atm) inside the hot can?
A. 3.1
B. 24
C.0.041
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Gas Laws
Your space ship has docked at a space station above Mars. The temperature inside the space station is 24oC at a pressure of 745mmHg. A balloon with a volume of 425mL drifts into the airlock where the temperature is -95oC and the pressure is 0.115 atm. What is the new volume of this balloon (assume it’s very elastic)?
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Dinitrogen oxide (N2O), laughing gas, is used by dentists as an anesthetic. If a 20.0 L tank of laughing gas contains 2.86 mol N2O at 23°C, what is the pressure in the tank?
Learning Check
Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings
A. 0.270 atm
B. 3.48 atm
C. 1.74 atm
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Gases in Chemical Equations
The volume or amount of a gas in a chemical reaction can be calculated from:
STP conditions or the Ideal Gas Law
Mole factors from the balanced equation
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STP and Gas Equations
What volume (L) of O2 gas is needed to completelyreact with 15.0 g of aluminum at STP?
4Al(s) + 3O2 (g) 2Al2O3(s)
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Gas Equations and Reactions
What volume (L) of Cl2 gas at 1.2 atm and 27°C is needed to completely react with 1.5 g of aluminum?
2Al(s) + 3Cl2 (g) 2AlCl3(s)
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Gas Laws and Stoichiometry Butane, C4H10, burns according to the equation:
2C4H10 (g) + 13O2 (g) 8CO2 (g) + 10 H2O (l)
What volume of CO2 measured at STP would be produced by
85.0 g of C4H10?
A. 131L
B. 32.8L
C. 65.5 L
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Gas Laws and Stoichiometry, II Oxygen gas can be prepared in the lab by the decomposition of
potassium nitrate according to the equation: 2KNO3 (s) 2KNO2 (s) + O2 (g)
What mass of KNO2 forms along with 14.5 L of O2 measured at 1.00atm and 25 oC?
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Ideal Gas Law - expanded
PV = nRT ; n = grams/Molar Mass
n = g/MM
PV = gRT MM
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What is the molar mass of a gas if 0.250 g of the gas occupies 215 mL at 0.813 atm and 30.°C?
A. 3.52g/mol B. 17.8g/mol C. 35.6g/mol
Molar Mass of a Gas
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Density of a Gas continued….
What is the density of ammonia gas, NH3(g), at 745 mmHg and 65oC?
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Density = Molar mass
Molar volume
Density = grams/mole = grams
L/mole L
Density of a Gas at STP
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Density of a Gas
Calculate the density in g/L of O2 gas at STP.