High School Chemistry : Gases and Gas Laws

Study concepts, example questions & explanations for High School Chemistry

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Example Questions

Example Question #1 : Using Avogadro's Law

 of nitrogen gas are contained in a  container. The gas exerts a pressure of  on the container.

If pressure is kept constant, what is the final molar amount of gas present in the container if gas is added until the volume has increased to ?

Possible Answers:

Correct answer:

Explanation:

Since pressure is kept constant, we can directly compare the moles of gas in the container and volume using Avogadro's law. Since moles of gas and volume are on opposite sides of the ideal gas law, the two variables are directly proportional to one another.

Avogadro's law is written as follows:

First, we will need to convert the initial mass of gas to moles. It is important to remember that nitrogen gas is diatomic!

Use this value and the given volumes to solve for the final amount of gas in the container.

 

Example Question #2 : Using Avogadro's Law

If 1.0mol of helium gas (He) at standard temperature and pressure (STP) has a volume of 22.4L, how many moles of carbon tetrachloride gas (CCl4) will be present in a container with a volume of 22.4L?

Possible Answers:

Correct answer:

Explanation:

Avogadro's Law states that two gases at the same temperature and volume will have an equal number of molecules, and therefore the same number of moles.

It does not matter that helium has one atom per molecule while carbon tetrachloride has five atoms per molecule. Note that the given volume per mole of gas at STP is standard, and true for any gas. At STP, one mole of gas will always have a volume of 22.5L, regardless of its identity.

Example Question #1 : Using Avogadro's Law

How many neutrons are in 10 moles of aluminum?

Possible Answers:

Correct answer:

Explanation:

To find the number of neutrons, we must convert the moles to atoms by multiplying the moles by Avogadro's number .

Now looking at the periodic table, the neutrons per atom can be found by subtracting the atomic weight by the atomic number:

Thus there are 14 neutrons in each atom of aluminum.

Example Question #31 : Gases And Gas Laws

Which of the following is a condition of the ideal gas law?

Possible Answers:

The gas molecules must be moving at a slow speed

The gas molecules must interact with each other

The gas molecules must be in specific mole ratios

The gas molecules must adhere to the container wall

The gas molecules do not have volume

Correct answer:

The gas molecules do not have volume

Explanation:

The ideal gas law has some conditions that must be met, conditions that certainly cannot be met in the real world. These conditions include that the gases cannot interact with one another, gases must be moving in a random straight-line fashion, gas molecules must not take up any space, and gases must be in perfect elastic collisions with the walls of the container. These conditions minimize the effect that gas molecules have on one other, allowing a prediction based on completely random and unimpeded molecular movement. In reality, these conditions are impossible. All real gas molecules have a molecular volume and some degree of intermolecular attraction forces.

Example Question #1 : Using The Ideal Gas Law And Combined Gas Law

container of gas has a pressure of  at a temperature of . The container is expanded to , and the temperature is increased to .

What is the final pressure of the container?

Possible Answers:

Correct answer:

Explanation:

In this case, two variables are changed between the initial and final containers: volume and temperature. Since we are looking for the final pressure on the container, we can use the combined gas law in order to solve for the final pressure:

When using the ideal gas law, remember that temperature must be in Kelvin, not Celsius, so we will need to convert.

Use the given values to solve for the final pressure.

Example Question #33 : Gases And Gas Laws

At STP, an unknown gas has a density of .

Based on this information and the periodic table, what is the identity of the gas in the container?

Possible Answers:

Fluorine gas

Neon

Nitrogen gas

Krypton

Correct answer:

Fluorine gas

Explanation:

Once again, we can use the ideal gas law in order to solve for the unknown gas. We will start again with the ideal gas law:

Density has the units of mass over volume, which means that we can rearrange the ideal gas law so that density is on one side of the equation. However, we need to substitute one of the values so mass is also in the equation. Remember that moles are equal to mass divided by molar mass, so we can rewrite "n" in order to solve for density:

STP means that the container is at 1 atmosphere of pressure and 273 Kelvin. Knowing this, we can solve for molar mass:

Fluorine gas has a molar mass of 38.00 grams per mol. As a result, we determine that fluorine gas is the unknown gas in the container.

Example Question #31 : Gases And Gas Laws

 of an unknown gas are contained in a  container. The container has a pressure of at a temperature of .

Based on this information and the periodic table, which of the following gases is in the container?

Possible Answers:

Neon

Argon

Helium

Nitrogen gas

Correct answer:

Argon

Explanation:

In order to determine the gas being contained, we are going to need to rewrite the ideal gas law. The ideal gas law is written as follows:

The number of moles of a gas can be rewritten as the mass of the gas divided by its molar mass. Knowing this, we can rewrite the equation, and solve for the molar mass of the gas.

Use the given values in this equation to solve for the molar mass. Remember to first convert degree Celsius to Kelvin!

Now that we have solved for the molar mass, we can see which gas has this molar mass on the periodic table. Argon has a molar mass of 39.95 grams per mole, so we can determine that argon is the gas in the container. 

Example Question #2 : Using The Ideal Gas Law And Combined Gas Law

Which law is represented by the following formula?

Possible Answers:

Charles's law

Dalton's law 

Combined gas law

Boyle's law

Ideal gas law

Correct answer:

Combined gas law

Explanation:

The combined gas law takes Boyle's, Charles's, and Gay-Lussac's law and combines it into one law.

It is able to relate temperature, pressure, and volume of one system when the parameters for any of the three change.

Boyle's law relates pressure and volume:

Charles's law relates temperature and volume:

Gay-Lussac's law relates temperature and pressure:

The ideal gas law relates temperature, pressure, volume, and moles in coordination with the ideal gas constant:

Example Question #1 : Using The Ideal Gas Law And Combined Gas Law

A scuba diver uses compressed air to breath under water. He starts with an air volume of  at sea level () at a temperature of . What is the volume of air in his tank at a depth of  () and a temperature of

Possible Answers:

Correct answer:

Explanation:

This question requires the combined equation of the individual gas laws:

To use this equation, we first need to convert the given temperatures to Kelvin.

We now know the initial pressure, volume, and temperature, allowing us to solve the left side of the equation.

Use the given values for the final temperature and pressure to solve for the final volume.

Example Question #1 : Using The Ideal Gas Law And Combined Gas Law

sample of helium gas at  and a pressure of  is used to inflate a balloon. What is the volume this gas occupies when the temperature reaches  at a pressure of during the inflation?

Possible Answers:

Correct answer:

Explanation:

This question requires s to use the combined gas law:

We know the initial pressure, temperature, and volume, allowing us to solve for the left side of the equation.

We are also given the final pressure and temperature. Using these values on the right side of the equation we can solve for the final volume.

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