Gas Laws
If I start with 30 mL at 200 K and heat it to 400 K, what would be the new volume if the pressure is halved. The initial pressure was 644 mm Hg.
(P1V1)/T1 = (P2V2)/T2
P1 = 644 mm Hg, P2 = 322 mm Hg, V1 = 30 mL
T1 = 200 K, T2 = 400 K
Final answer: 120 mL
What is the value for R, and what are its units?
0.0821 L*atm/mol*K
What are the STP values for each unit of pressure (2 of them; one in atm, the other in mm Hg)?
1 atm, 760 mmHg
What law relates volume and temperature
Charles Law
If I start with 0.90 atm at 10.0 Celsius and cool it to 3.0 Celsius, what would be the new pressure? The gas expands from 235 mL to 421 mL.
(P1V1)/T1 = (P2V2)/T2
P1 = 0.9 atm, T1 = 293 K, T2 = 276 K, V1 = 235 mL, V2 = 421 mL
Final answer: P = 0.49 atm
If we maintain a pressure of 748 mm Hg at 25 C and if the volume occupied by the gas is 2.89 L, how many mole of gas do we have?
P = 748 mm Hg ×(1 atm/760 mm Hg) = 0.984 atm, V = 2.89 L, T = 25+273 = 298 K
Use PV = nRT; R = .0821 Latm/molK
Answer:0.116 mole
What is STP?
Temperature = 0 C or 273 K
Pressure= 1 atm , or 760 mm Hg
Which law relates temperature and pressure
Gay Lussac's Law
If an aerosol can is heated up, and the volume remains constant because the container is rigid, which quantity must change?
Pressure
If I have 0.068 mole of gas at 42 C, and the gas occupies 1.75 L, find the pressure.
T = 42 + 273 = 315 K, n = 0.068 mol, V = 1.75 L
Use PV = nRT; R = 0.0821 Latm/molK
Answer: 1.00 atm
Will the ideal gas law work better for water in the gas state or O2 in the gas state? Why?
The ideal gas law works better for O2 in the gas state. This is because O2 experiences London dispersion forces because it is nonpolar. H2O experiences hydrogen bonding. Since O2 experiences a weaker intermolecular force than H2O, the ideal gas law is more applicable.
Which law relates temperature, volume, and pressure
Combined gas law
Which law best explains why hot air is less dense than cold air? Remember that density = mass/volume
Temperature has no effect on mass, but since the air is not trapped in a rigid container, as the temperature increases, the air expands, increasing the volume. The bigger the volume, the lower the density.
If the volume occupied by He gas at STP is 5.6 L, find the grams of He. The atomic mass of He is 4.03 g/mol.
P=1.00 atm, T = 273 K, V = 5.6 L
PV = nRT; R = 0.0821 Latm/molK
n = 0.25 mole He; 0.25 mol×(4.03 g/1 mol)
Answer:1.01 g
Does the ideal gas law work better for gases at high or low temperatures? Why?
The ideal gas laws work better at higher temperatures for two reasons. At higher temperatures, intermolecular forces weaken
Also, the volume tends to increase at higher temperatures, lowering the density.
Which law has a temperature, pressure, volume, constant, and moles as variables.
Ideal gas law
Which law best explains why a can of air freshener will explode if left in a car parked with the windows closed on a hot day?
Hint: The can is not flexible. So do you think the can's volume changes easily?
Gay-Lussac's Law P1/T1 = P2/T2 because the volume remains constant
Given: 2KClO3(s) ---> 2KCl(s) + 3O2(g)
If the pressure is maintained at 732 mm Hg, temperature at 20 C, then if we start with 12.3 g of KClO3 (molar mass is 122.6 g/mol), find the volume of O2 gas produced.
Mole O2: 12.3 g KClO3 × (1 mol KClO3/122.6 g KClO3)×(3 mole O2/2 mole KClO3) = 0.15 mole
T = 20+273 = 293 K, P: 732 mm Hg×(1 atm/760 mm Hg) = 0.963 mol...use PV = nRT
Answer: V = 3.75 L
If you have two different gas samples, both of which is nonpolar, which gas is more likely to be an ideal gas...the one with lower molar mass or the one with higher molar mass? Explain.
The one with lower molar mass. Nonpolar molecules experience London dispersion forces. London dispersion forces are weaker for lower molar masses. The weaker the intermolecular force, the more ideal the gas.
Which law relates volume and moles?
Avogadro's Law
V1/n1= v2/n2