Fluids and Gases - MCAT Chemical and Physical Foundations of Biological Systems
Card 0 of 658
Five moles of nitrogen gas are present in a 10L container at 30oC. What is the pressure of the container?
Five moles of nitrogen gas are present in a 10L container at 30oC. What is the pressure of the container?
Using the ideal gas law equation we can find that P= nRT/V. We then plug in the given values.
Solving for P gives us 12.4atm.
Note: 30oC must be converted into Kelvin by adding 273K
Using the ideal gas law equation we can find that P= nRT/V. We then plug in the given values.
Solving for P gives us 12.4atm.
Note: 30oC must be converted into Kelvin by adding 273K
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Solid A has a volume of 
and a density of 
. Solid B is cube with sides of 
and has a density of 
.
What is the difference in mass between the two solids?
Solid A has a volume of
What is the difference in mass between the two solids?
The formula for density is:
In the question, we are given the densities of both solids and a means to find their volumes. Using these values, we will be able to determine the mass of each solid.
Now that we know both masses, we can find the difference.
The formula for density is:
In the question, we are given the densities of both solids and a means to find their volumes. Using these values, we will be able to determine the mass of each solid.
Now that we know both masses, we can find the difference.
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The law of Laplace states what relationship between that the tension in the wall of a bubble and the radius of the bubble?
The law of Laplace states what relationship between that the tension in the wall of a bubble and the radius of the bubble?
The law of Laplace states that wall tension in a bubble, balloon, pulmonary alveolus, or blood vessel is directly proportional to the radius and the internal pressure.
Law of Laplace: 
In other words, as the size of the bubble increases at constant pressure or as the pressure increases at constant size, the wall tension needed to keep the bubble from increasing in size is increased. In part, this explains why aneurysms on blood vessels burst.
The law of Laplace states that wall tension in a bubble, balloon, pulmonary alveolus, or blood vessel is directly proportional to the radius and the internal pressure.
Law of Laplace:
In other words, as the size of the bubble increases at constant pressure or as the pressure increases at constant size, the wall tension needed to keep the bubble from increasing in size is increased. In part, this explains why aneurysms on blood vessels burst.
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Diffusion can be defined as the net transfer of molecules down a gradient created by differing concentrations of the molecule in different locations. This is a passive, spontaneous process and relies on the random movement of molecules and Brownian motion. Diffusion is an important biological process, especially in the respiratory system where oxygen diffuses from alveoli, the basic units of lung mechanics, to red blood cells in the capillaries.
Figure 1 depicts this process, showing an alveolus separated from neighboring cells by a capillary with red blood cells. The partial pressures of oxygen and carbon dioxide are given. One equation used in determining gas exchange is Fick's law, given by:
In this equation, 
is the flow rate. Area and thickness refer to the permeable membrane through which the gas passes_—_in this case, the wall of the alveolus. 
and 
refer to the partial pressures upstream and downstream, respectively. 
, the diffusion constant of the gas, is defined as:
During inspiration, the diaphragm contracts and allows oxygen to rush into the lungs. How would a change in average airway diameter affect the speed at which oxygen moves?
Diffusion can be defined as the net transfer of molecules down a gradient created by differing concentrations of the molecule in different locations. This is a passive, spontaneous process and relies on the random movement of molecules and Brownian motion. Diffusion is an important biological process, especially in the respiratory system where oxygen diffuses from alveoli, the basic units of lung mechanics, to red blood cells in the capillaries.
Figure 1 depicts this process, showing an alveolus separated from neighboring cells by a capillary with red blood cells. The partial pressures of oxygen and carbon dioxide are given. One equation used in determining gas exchange is Fick's law, given by:
In this equation,
During inspiration, the diaphragm contracts and allows oxygen to rush into the lungs. How would a change in average airway diameter affect the speed at which oxygen moves?
Note, two of the choices say essentially say the same relationship. Therefore, one can immediately infer that they are wrong. The question is based off of knowledge of fluid dynamics. Typically, a decrease in airway diameter will provide more resistance and thus lower the speed at which a fluid (or gas) will move. Think about blowing air through a series of straws of narrowing diameter; the narrower the straw, the harder it is to blow air; therefore, a decrease in airway diameter would cause an decrease in oxygen speed.
Note, two of the choices say essentially say the same relationship. Therefore, one can immediately infer that they are wrong. The question is based off of knowledge of fluid dynamics. Typically, a decrease in airway diameter will provide more resistance and thus lower the speed at which a fluid (or gas) will move. Think about blowing air through a series of straws of narrowing diameter; the narrower the straw, the harder it is to blow air; therefore, a decrease in airway diameter would cause an decrease in oxygen speed.
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Which of the following would tend to decrease the viscosity of a liquid flowing through a pipe?
Which of the following would tend to decrease the viscosity of a liquid flowing through a pipe?
The factors that influence viscosity are:
1. The molecular structure of the given liquid (i.e. what liquid is flowing)
2. Temperature
3. Extreme pressure
Liquids become less viscous with increased temperature. As temperature increases, the molecules move faster relative to one another and spend less time in contact with each other. This behavior causes the intermolecular forces to decrease, so the viscosity decreases.
The factors that influence viscosity are:
1. The molecular structure of the given liquid (i.e. what liquid is flowing)
2. Temperature
3. Extreme pressure
Liquids become less viscous with increased temperature. As temperature increases, the molecules move faster relative to one another and spend less time in contact with each other. This behavior causes the intermolecular forces to decrease, so the viscosity decreases.
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Five moles of nitrogen gas are present in a 10L container at 30oC. What is the pressure of the container?
Five moles of nitrogen gas are present in a 10L container at 30oC. What is the pressure of the container?
Using the ideal gas law equation we can find that P= nRT/V. We then plug in the given values.
Solving for P gives us 12.4atm.
Note: 30oC must be converted into Kelvin by adding 273K
Using the ideal gas law equation we can find that P= nRT/V. We then plug in the given values.
Solving for P gives us 12.4atm.
Note: 30oC must be converted into Kelvin by adding 273K
Compare your answer with the correct one above
Solid A has a volume of and a density of . Solid B is cube with sides of and has a density of .
What is the difference in mass between the two solids?
Solid A has a volume of
What is the difference in mass between the two solids?
The formula for density is:
In the question, we are given the densities of both solids and a means to find their volumes. Using these values, we will be able to determine the mass of each solid.
Now that we know both masses, we can find the difference.
The formula for density is:
In the question, we are given the densities of both solids and a means to find their volumes. Using these values, we will be able to determine the mass of each solid.
Now that we know both masses, we can find the difference.
Compare your answer with the correct one above
Diffusion can be defined as the net transfer of molecules down a gradient created by differing concentrations of the molecule in different locations. This is a passive, spontaneous process and relies on the random movement of molecules and Brownian motion. Diffusion is an important biological process, especially in the respiratory system where oxygen diffuses from alveoli, the basic units of lung mechanics, to red blood cells in the capillaries.
Figure 1 depicts this process, showing an alveolus separated from neighboring cells by a capillary with red blood cells. The partial pressures of oxygen and carbon dioxide are given. One equation used in determining gas exchange is Fick's law, given by:
In this equation, is the flow rate. Area and thickness refer to the permeable membrane through which the gas passes_—_in this case, the wall of the alveolus. and refer to the partial pressures upstream and downstream, respectively. , the diffusion constant of the gas, is defined as:
During inspiration, the diaphragm contracts and allows oxygen to rush into the lungs. How would a change in average airway diameter affect the speed at which oxygen moves?
Diffusion can be defined as the net transfer of molecules down a gradient created by differing concentrations of the molecule in different locations. This is a passive, spontaneous process and relies on the random movement of molecules and Brownian motion. Diffusion is an important biological process, especially in the respiratory system where oxygen diffuses from alveoli, the basic units of lung mechanics, to red blood cells in the capillaries.
Figure 1 depicts this process, showing an alveolus separated from neighboring cells by a capillary with red blood cells. The partial pressures of oxygen and carbon dioxide are given. One equation used in determining gas exchange is Fick's law, given by:
In this equation,
During inspiration, the diaphragm contracts and allows oxygen to rush into the lungs. How would a change in average airway diameter affect the speed at which oxygen moves?
Note, two of the choices say essentially say the same relationship. Therefore, one can immediately infer that they are wrong. The question is based off of knowledge of fluid dynamics. Typically, a decrease in airway diameter will provide more resistance and thus lower the speed at which a fluid (or gas) will move. Think about blowing air through a series of straws of narrowing diameter; the narrower the straw, the harder it is to blow air; therefore, a decrease in airway diameter would cause an decrease in oxygen speed.
Note, two of the choices say essentially say the same relationship. Therefore, one can immediately infer that they are wrong. The question is based off of knowledge of fluid dynamics. Typically, a decrease in airway diameter will provide more resistance and thus lower the speed at which a fluid (or gas) will move. Think about blowing air through a series of straws of narrowing diameter; the narrower the straw, the harder it is to blow air; therefore, a decrease in airway diameter would cause an decrease in oxygen speed.
Compare your answer with the correct one above
Which of the following would tend to decrease the viscosity of a liquid flowing through a pipe?
Which of the following would tend to decrease the viscosity of a liquid flowing through a pipe?
The factors that influence viscosity are:
1. The molecular structure of the given liquid (i.e. what liquid is flowing)
2. Temperature
3. Extreme pressure
Liquids become less viscous with increased temperature. As temperature increases, the molecules move faster relative to one another and spend less time in contact with each other. This behavior causes the intermolecular forces to decrease, so the viscosity decreases.
The factors that influence viscosity are:
1. The molecular structure of the given liquid (i.e. what liquid is flowing)
2. Temperature
3. Extreme pressure
Liquids become less viscous with increased temperature. As temperature increases, the molecules move faster relative to one another and spend less time in contact with each other. This behavior causes the intermolecular forces to decrease, so the viscosity decreases.
Compare your answer with the correct one above
8 liters of an ideal gas is in an isolated container at 30 degrees Celsius. The container is heated at constant pressure until its volume is doubled. What is the new temperature of the gas?
8 liters of an ideal gas is in an isolated container at 30 degrees Celsius. The container is heated at constant pressure until its volume is doubled. What is the new temperature of the gas?
At constant pressure, 
, where the temperatures are measured in Kelvin (absolute temperature).
First, convert the given temperature (C) to Kelvin (K).
K = C + 273 = 30 + 273 = 303K
Plug the temperature and volumes into the above equation and solve for the final temperature.
Convert this value back to Celsius.
C = K - 273 = 606 - 273 = 333oC
At constant pressure,
First, convert the given temperature (C) to Kelvin (K).
K = C + 273 = 30 + 273 = 303K
Plug the temperature and volumes into the above equation and solve for the final temperature.
Convert this value back to Celsius.
C = K - 273 = 606 - 273 = 333oC
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What is the temperature of a 1L container at STP after the pressure is doubled?
What is the temperature of a 1L container at STP after the pressure is doubled?
Using Gay-Lussac's Law, which is 
, we can find the change in temperature when the pressure is doubled.
Because the problem states that the original conditions were at STP, we know that pressure is 1atm and temperature is 273K. Since pressure and temperature are directly proportional, doubling pressure will also double the temperature. The final temperature will be 546K.
Using Gay-Lussac's Law, which is
Because the problem states that the original conditions were at STP, we know that pressure is 1atm and temperature is 273K. Since pressure and temperature are directly proportional, doubling pressure will also double the temperature. The final temperature will be 546K.
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Regarding the following sets of conditions, which answer option gives the correct listing of systemic pressures from greatest to least?
Regarding the following sets of conditions, which answer option gives the correct listing of systemic pressures from greatest to least?
This question asks for you to look at a set of conditions for gases, and determine relative pressures. The best equation to use for quick calculation and relation is the ideal gas law, given by:
Rearranging this, and removing the constant (since it will not affect relative pressure), we can generate a proportionality of pressure to the other variables.
We can use this proportionality with each option to determine their rankings by pressure.
This question asks for you to look at a set of conditions for gases, and determine relative pressures. The best equation to use for quick calculation and relation is the ideal gas law, given by:
Rearranging this, and removing the constant (since it will not affect relative pressure), we can generate a proportionality of pressure to the other variables.
We can use this proportionality with each option to determine their rankings by pressure.
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A sealed container holds three moles of gas at 1atm and 200K. Its pressure is to 2atm. What will be the resulting temperature in the container?
A sealed container holds three moles of gas at 1atm and 200K. Its pressure is to 2atm. What will be the resulting temperature in the container?
In the problem, the volume and the number of moles are constant and the temperature and pressure are the only two variables that are changing. Using the ideal gas law we can find that temperature and pressure are directly proportional. When pressure increases by a factor of two, temperature will also increase by a factor of two.
In the problem, the volume and the number of moles are constant and the temperature and pressure are the only two variables that are changing. Using the ideal gas law we can find that temperature and pressure are directly proportional. When pressure increases by a factor of two, temperature will also increase by a factor of two.
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If one mole of oxygen gas occupies a 5L container at 300K, what is the pressure in the container?
If one mole of oxygen gas occupies a 5L container at 300K, what is the pressure in the container?
Using the ideal gas law, 
, we can solve for pressure.
Using the ideal gas law,
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Recall that the ideal gas law states that 
, where 
.
If there are 5g of hydrogen gas in a 10L chamber at 32°C, what would be the pressure?
Recall that the ideal gas law states that
If there are 5g of hydrogen gas in a 10L chamber at 32°C, what would be the pressure?
Using the equation 
and solving for P you get, 
.
Recall that hydrogen forms a diatomic molecule when in gas form. This should always be an assumption when working with hydrogen gas on the MCAT. When we convert 5g to moles, we must use a conversion factor of 2g/mol.
Temperature must be converted to Kelvin. You must have this conversion memorized for the MCAT.
Now we can solve for P.
Using the equation
Recall that hydrogen forms a diatomic molecule when in gas form. This should always be an assumption when working with hydrogen gas on the MCAT. When we convert 5g to moles, we must use a conversion factor of 2g/mol.
Temperature must be converted to Kelvin. You must have this conversion memorized for the MCAT.
Now we can solve for P.
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A certain gas is initially at a pressure of 2atm in a volume of 5L. It then experiences a decrease in volume to 2L, and is held at a constant temperature throughout the process. What is the new pressure?
A certain gas is initially at a pressure of 2atm in a volume of 5L. It then experiences a decrease in volume to 2L, and is held at a constant temperature throughout the process. What is the new pressure?
Since this is an isothermal change (constant temperature), this falls under Boyle's law.
Taking this equation and solving for the new pressure (P2) we come up with 5atm.
Since this is an isothermal change (constant temperature), this falls under Boyle's law.
Taking this equation and solving for the new pressure (P2) we come up with 5atm.
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15L of a gas is held at constant pressure as the temperature increases from 300K to 350K. What is the new volume?
15L of a gas is held at constant pressure as the temperature increases from 300K to 350K. What is the new volume?
Charles's Law states that 
. To solve for the final volume, we simply plug in our given values to this equation.
This law applies only for isobaric (constant pressure) changes.
Charles's Law states that
This law applies only for isobaric (constant pressure) changes.
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A balloon filled with one mole of an ideal gas is leaking molecules at a constant rate of
.
After 75 hours, the pressure is half of the initial pressure. What is the new volume in terms of the initial volume, 
?
Assume temperature remains constant.
A balloon filled with one mole of an ideal gas is leaking molecules at a constant rate of
After 75 hours, the pressure is half of the initial pressure. What is the new volume in terms of the initial volume,
Assume temperature remains constant.
We can use the given values to determine how many moles of the gas have leaked out after 75 hours.
We now know that the balloon started with one mole, and that 0.75 moles have leaked. This means that 0.25 moles remain in the balloon. We now have our initial and final mole values and pressure values. We can rearrange the ideal gas law to isolate the variables we need, assuming that the temperature is constant.
Using our proportions, we can try to solve for the final volume. For simplicity, assume the initial pressure is 1 and the final pressure is 0.5.
We can use the given values to determine how many moles of the gas have leaked out after 75 hours.
We now know that the balloon started with one mole, and that 0.75 moles have leaked. This means that 0.25 moles remain in the balloon. We now have our initial and final mole values and pressure values. We can rearrange the ideal gas law to isolate the variables we need, assuming that the temperature is constant.
Using our proportions, we can try to solve for the final volume. For simplicity, assume the initial pressure is 1 and the final pressure is 0.5.
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A 
container holds 
of oxygen gas at a temperature of 
. The temperature remains constant and the volume of the container is increased to 
. What is the final pressure of the gas in terms of the initial pressure, 
?
A
The amount of gas is irrelevant. If the temperature is held constant and the volume is increased by a factor of three, the resulting pressure is decreased by a factor of three according to Boyle’s Law.
The amount of gas is irrelevant. If the temperature is held constant and the volume is increased by a factor of three, the resulting pressure is decreased by a factor of three according to Boyle’s Law.
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Which of the following would not cause a decrease in the pressure of a gas in a sealed container?
Which of the following would not cause a decrease in the pressure of a gas in a sealed container?
A decrease in pressure means a decrease in gas particle collisions. The only option that would not cause a decrease in collisions is adding moles of a different gas. Even though different molecules are added, there will be greater pressure as particle collisions will be more frequent.
Reducing temperature slows the gas particles, thus decreasing the frequency of collisions. Similarly, increasing the volume of the container and removing particles will cause a decrease in collisions, and subsequent pressure.
A decrease in pressure means a decrease in gas particle collisions. The only option that would not cause a decrease in collisions is adding moles of a different gas. Even though different molecules are added, there will be greater pressure as particle collisions will be more frequent.
Reducing temperature slows the gas particles, thus decreasing the frequency of collisions. Similarly, increasing the volume of the container and removing particles will cause a decrease in collisions, and subsequent pressure.
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