Mastering Chemistry Chp 5
One mole of an ideal gas is sealed in a 22.4-L container at a pressure of 1 atm and a temperature of 273 K. The temperature is then increased to 310.K , but the container does not expand. What will the new pressure be? The most appropriate formula for solving this problem includes only which variables? You have determined in Part A that P and T are the only variables needed in the formula. Which of the following relationships holds? PT is constant P/T is constant
1.14 atm The number of moles and liters were given, but they are not necessary for solving the problem. P,T. Since temperature increases, it must be included in your formula. Since you are solving for pressure, it much also be included. However, since the number of moles and the volume remain the same, they can be excluded. P/T is constant. Since the quantity P/T is constant, it follows that P1/T1=P2/T2.
The mass of an evacuated 255 mL flask is 143.187g. The mass of the flask filled with 270 torr of an unknown gas at 25C is 143.290 g. Calculate the molar mass of the unknown gas
143.290-143.187=.103 270/760=.355 moles gas= pV/RT= (.355 X .255)/(.08206 X 298)=.00370 .103/.00370=27.7
A balloon was filled to a volume of 2.50 L when the temperature was 30.0 C. What would the volume become if the temperature dropped to 11.0C.
2.34 L The first step is to change the temperature to K. So 30.0+273.15=303.15, and 11.0+273.15=284.15. So, 2.50L/303.15=X/284.15. =2.34L
A sample of gas has an initial volume of 4.3L at a pressure of 760 mmHg. If the volume of the gas is increased to 9.4L, what will the pressure be?
350 mmHg
A 50.0 mL sample of gas in a cylinder is warmed from 18C to 86 C. What is its volume at the final temperature?
61.7 mL. Change C into K. V1/T1=V2/T2 50.0mL/291.15 = V2/359.15=61.7mL
An experiment shows that a 245 mL gas sample has a mass of .432g at a pressure of 753 mmHg and a temperature of 29C. What is the molar mass of the gas?
753mmHg=0.99 atm 245 mL= .245L 29C= 302.15K) PV/RT (.99 X .245)/(.08206 X 302.15)=.00978 0.00978 X .432= 44.1
A mixture of 8.6 CH4 and 8.6g Xe is placed in a container and the total pressure is found to be 0.47 atm. Find the partial pressure of CH4.
CH4: mole=mass/molar mass mole= 8.6 g/ 16.04g/mol mole=.5362 Xe: mole= mass/molar mass mole= 8.6g/131.293 mole=.063217 .5362+.063217=.599417 .5362/.599417=.8945 .8945X.47= .42g
How many air molecules are in a 14.0 X 12.0 X 10.0 ft room? Assume atmospheric pressure of 1.00 atm, a room temperature of 20.0C, and ideal behavior. Volume conversions: There are 28.2 liters in one cubic foot.
Change 20C to 293.15K. (14 X 12 X 10) X (28.2 L/ft^3) X (273.15/293.15) / (22.4 L/mol) X (6.022 X 10^23 molecules/mol) 1.18 X 10^27 molecules. 22.4 is STP.
Diffusion or Effusion When a coworker microwaves popcorn, you can smell the vapors in your office 5 minutes later. Hair spray applied in the bedroom can be smelled in the hallway a short time later. When you drive over a nail the volume of the tire decreases slowly over time as air escapes through the hole. A balloon in a constant environment gets smaller and smaller over the course of a week as gas leaks through small holes in the rubber.
Diffusion Diffusion Effusion Effusion
An empty container is not really empty if in contains air. how many moles of oxygen are in an empty two liter cola bottle at atm pressures (1 atm) and room temperature (25C)? Assume ideal behavior.
Find moles of O2 PV=nRT (.21 atm of O2) X (2 L)= n(0.08206 L-atm/mol-k) X (298.15) =0.017
An "empty" container is not really empty if it contains air. How many moles of nitrogen are in an "empty" two liter cola bottle at atmospheric pressure and room temperature (25C)? Assume ideal behavior.
Find the moles of N2 PV=nRT (.78 atm of N2) (2 L)= n(0.08206 L-atm/mol-K) X (298.15) =0.0638 mol of n2
Which statements about a sample of gas containing molecules of different masses are true? -More massive gas molecules in the sample have lower rms speed than less massive ones. -The rms speed depends only on temperature, and so allt ypes of particles in the sample have the same rms speed. -More-massive gas molecules in the sample have higher rms speed than less-massive ones.
More massive gas molecules in the sample have lower rms speed than less massive ones. The average kintetic energy depeneds only on the temperature. However, a heavier molecule will move more slowly than a lighter molecule if they both have the same kinetic energy.
Refrigerators are usually kept at about 5C, while room temperature is about 20C. If you were to take an "empty" sealed 2-liter soda bottle at room temperature and place it in the fridge, would you expect it to contract to one-fourth its original volume?
No, because Celsius is not an absolute temperature scale. Note that 20C=293K and 5C=278K. So the temperature has not decreased by very much at all, certainly not by a factor of four. Therefore, the change in size of the plastic bottle would not be very noticeable.
Give the molar volume value for a gas at STP.
PV=nRT (1.00 atm)(V)=1 mol (.08206 L-atm/mol-k)(273.15K) V= 22.414 Liters.
What is the volume occupied by 12.8g of argon gas at a pressure of 1.32 atm and a temperature of 315K?
PV=nRT P= 1.32 atm V=? n= 12.8/39.948 (molar mass)- .3204 R=0.08206 T=315K. (1.32atm)V=(.3204)X (0.08206) X (315) =6.26 L
What are some common units of pressure? Check all that apply -Pa -J -mmLi -atm -in Hg -m2/s -mmHg -torr psi
Pa atm in Hg mmHg torr psi
A closed container is filled with oxygen. The pressure in the contaier is 375,000 Pa. What is the pressure in millimeters of mercury?
Remember that 1 atm= 760 mmHg= 101,325 Pa. So, 375,000 Pa X (760 mmHg/101,325 Pa) = 2812.73 mmHg or 2810 mmHg.
On a rainy day, a barometer reads 745 mmHg. Convert this value to atmospheres.
Remember that 1 atm=760 mmHg= 101,325 Pa. 745mmHg/760mmHg = 0.980 atm. The standard atmospheric pressure at sea level is 1 atm (760 mmHg). Higher pressure usually means sunny and dry weather, and lower pressure often brings clouds and precipitation.
Lithium reacts with nitrogen gas according to the following reaction:6Li(s) + N2 (g) -> 2Li3N(s) What mass of lithium is required to react completely with 60.0mL of N2 gas at STP.
STP is defined as 0C and 1 atm pressure. The thing to know is that 1 mole of any ideal gas occupies 22.414 liters at STP. (.0600L)/(22.414 L/mol) X (6 mol Li/ 1 mol N2) X (6.9412 g Li/mol)= 0.111 g Li
How does the density of gas depend on temperature?
The density will decrease as temperature increases.
How does the density of a gas depend on the molar mass of the gas?
The density will increase as molar mass of the gas increases.
How does the density of gas depend on pressure?
The density will increase as pressure increases.
What is the pressure (in atmospheres) of the gas inside the container connected to an open-end, mercury-filled manometer. The atmospheric pressure is 0.95 atm. With a gas tube measurement of 18 cm.
The idea is that you read the manometer directly as gauge pressure (pressure relative to atmospheric). end open to atmopshere means the pressure in the vessel is 18cmHg > than atmospheric. Pvessel= 0.95 atm + 18cmHg= 0.95 atm = (18cmHg X 1 atm/ 76 mmhG)= 1.19 atm. Mercury is used in barometers and manometers because it has the higest density among liquids at room temperature (13.6 g/mL). It is possible to make a manometer filled with any liquid, and it would work, but the tube would need to be much longer. When the density of a liquid is low, relatively small changes in pressure would result in large changes in the level of the liquid.
Define molar volume for a gas at STP.
The molar volume of an ideal gas is the volume occupied by one mole of gas at T=0C(273K) and P= 1.00 atm).
According to Charle's law, for a fixed quantity of gas at a constant pressure, which of the given quantities is constant?
V/T
Avagadro's Law states that at a given temperature and pressure, what quantity is constant?
V/n Since V and n are directly proportional, the quantity V/n will always have the same value at a given pressure and temperature.
Air is about 78% nitrogen molecules and 21.0% oxygen molecules. Several other gases make up the remaining 1% of air molecules. What is the partial pressure of nitrogen at atmpsheric pressure (1 atm)? Assume ideal behavior. What is the partial pressure of oxygen in air at atmopsheric pressure (1 atm) Assume ideal behavior.
n2= .780 atm because 78 (from the 78%) 78/100=0.78 O2= 21 (beccause 21% oxygen) 21/100= .21 atm
Avogadro's Law
states that the volume of a gas is directly proportional to the number of moles of the gas, while pressure and temperature are kept constant (V/n=constant)
Charles's Law
states that the volume of a gas is directly proportional to the temperature of the gas, while pressure and number of moles are kept constant (V/T=constant). All temperature must be in kelvins when used in gas law calculations.
Boyle's Law
states that the volume of the gas varies inversely to the pressure on the gas, while temperature and number of moles are kept constant (PV= constant).
Compare the volume of 12.8g of helium to 12.8g of argon gas under indentical conditions
(1.32)(V)=(3.19)X(0.08206)(315)=62.47 The volume would be greater for helium gas. Helium has a lower atomic mass than argon. The same mass of helium gas would contain a greater number of moles and have a larger volume.
What is the temperature of .53 mol of gas at a pressure of 1.5atm and a volume of 10.1L?
(1.5atm)(10.1)=(.53)(.08206)T 15.15=/.0434918 350 K
Which of the following statements are true? Check all that apply. -The average speed of gas molecules decreases with decreasing temperature. -The temperature of a gas sample is independent of the average kinetic energy. -All the gas molecules in a sample cannot have the same kinetic energy. -There are gas molecules that move faster than the average. -The average kinetic energy of gas molecules increases with increasing temperature
-The average speed of gas molecules decreases with decreasing temperature. -All the gas molecules in a sample cannot have the same kinetic energy. -There are gas molecules that move faster than the average. -The average kinetic energy of gas molecules increase with increasing temperature.
What is the pressure in a 24.1L cylinder filled with 10.6g of oxygen gas at a temperature of 326?
.368 atm
If it takes three "breaths" to blow up a balloon to 1.2L, and each breath supplies the balloon with 0.060 moles of exhaled air, how many moles of air are in a 3.0 L balloon
.45 mol because V1/n1=V2/n2 n2= V2Xn1/V1= 3.0L X (3 breaths X .06 mol/breath)/ 1.2L n2=0.45
Rank the units of pressure from smallest to largest. 1 Pa 1 torr 1 psi 1 atm 1 in Hg 1 mmHg
1 Pa 1 tor & 1 mmHg 1 in Hg 1 psi 1 atm
