High School Chemistry : Gases and Gas Laws

Study concepts, example questions & explanations for High School Chemistry

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Example Questions

Example Question #382 : High School Chemistry

A gas occupies a volume of \displaystyle 7.82L at \displaystyle 82^oC. At what temperature, in Kelvin, will the volume of the gas be \displaystyle 6.45L

Possible Answers:

\displaystyle 20K

\displaystyle 293K

\displaystyle 254K

\displaystyle 355K

Correct answer:

\displaystyle 293K

Explanation:

Charles's law of gases indicates that, at a constant pressure, the volume of a gas is proportional to the temperature. This is calculated by the following equation:

\displaystyle \frac{V_1}{T_1}=\frac{V_2}{T_2}

Our first step to solving this equation will be to convert the given temperature to Kelvin.

\displaystyle 82^oC+273=355K

Using this temperature and the given volumes, we can solve for the final temperature of the gas.

\displaystyle \frac{7.82L}{355K}=\frac{6.45L}{T_2}

\displaystyle T_2=\frac{(355K)(6.45L)}{7.82L}

\displaystyle T_2=293K

Example Question #2 : Using Charles's Law

The graph depicted below represents which of the gas laws?

Charles__law_graph

Possible Answers:

Gay-Lussac's law

Boyle's law

Newton's third law

Charles's law

Correct answer:

Charles's law

Explanation:

The graph shows that there is a directly proportional relationship between the volume of a gas and temperature in Kelvin when kept at a constant pressure. This is known as Charles’s law and can be represented mathematically as follows:

\displaystyle \frac{V_1}{T_1}=\frac{V_2}{T_2}

Gay-Lussac's law shows the relationship between pressure and temperature. Boyle's law shows the relationship between pressure and volume. Newton's third law is not related to gas principles and states that for every force on an object, there is an equal and opposite force of the object on the source of force.

Example Question #11 : Gases And Gas Laws

A balloon filled with room temperature air (\displaystyle 22.0^{o}C) has a volume of \displaystyle 50.2\, mL. The balloon is taken outside on a hot summer day where the temperature is \displaystyle 36.6^{o}C. What will the volume of the balloon be after it is taken outside?

Possible Answers:

\displaystyle 52.7\,mL

\displaystyle 47.8\,mL

\displaystyle 0.02\,mL

\displaystyle 1820\,mL

Correct answer:

\displaystyle 52.7\,mL

Explanation:

We expect the volume to increase since volume and temperature are directly proportional. We know that if we heat something the material will expand so we shouldn't get a value that is smaller than our initial volume. Charles Law says that

\displaystyle \frac{V_{1}}{T_{1}}=\frac{V_{2}}{T_{2}}

where the stuff on the left is the initial volume and temperature and the stuff on the right is the final volume and temperature. First off, we MUST convert the temperatures to Kelvin to use Charles Law. This gives

\displaystyle T_{1}=22.0^{o}C+273=295K

\displaystyle T_{2}=36.6^{o}C+273=309.6K

Solving for the final volume,

\displaystyle V_{2}=\frac{V_{1}T_{2}}{T_{1}}

\displaystyle V_{2}=\frac{(50.2\,mL)(309.6K)}{(295K)}=52.7\,mL

Example Question #383 : High School Chemistry

An ideal gas exerts a pressure of \displaystyle \small 3atm in a \displaystyle \small 3L container. The container is at a temperature of \displaystyle \small 298K.

What will be the final pressure if the volume of the container changes to \displaystyle \small 2L?

Possible Answers:

\displaystyle 4atm

\displaystyle 4.5atm

\displaystyle 3.5atm

\displaystyle 2 atm

Correct answer:

\displaystyle 4.5atm

Explanation:

Since the volume of the gas is the only variable that has changed, we can use Boyle's law in order to find the final pressure. Since pressure and volume are on the same side of the ideal gas law, they are inversely proportional to one another. In other words, as one increases, the other will decrease, and vice versa.

Boyle's law can be written as follows:

\displaystyle P_{1}V_{1} = P_{2}V_{2}

Use the given volumes and the initial pressure to solve for the final pressure.

\displaystyle (3atm)(3L) = (2L)P_{2}

\displaystyle P_{2} = 4.5atm

Example Question #384 : High School Chemistry

What law is the following formula?

\displaystyle P_{1}V_{1}= P_{2}V_{2}

Possible Answers:

Combined gas law

Boyle's law

Gay-Lussac's law

Ideal gas law

Charles's law

Correct answer:

Boyle's law

Explanation:

Boyle's law relates the pressure and volume of a system, which are inversely proportional to one another. When the parameters of a system change, Boyle's law helps us anticipate the effect the changes have on pressure and volume.

\displaystyle P_1V_1=P_2V_2

Charles's law relates temperature and volume: \displaystyle \frac{V_1}{T_1}=\frac{V_2}{T_2}

Gay-Lussac's law relates temperature and pressure: \displaystyle \frac{P_1}{T_1}=\frac{P_2}{T_2}

The combined gas law takes Boyle's, Charles's, and Gay-Lussac's law and combines it into one law: \displaystyle \frac{P_{1}V_{1}}{T_{1}}=\frac{P_{2} V_{2}}{T_{2}}

The ideal gas law relates temperature, pressure, volume, and moles in coordination with the ideal gas constant: \displaystyle PV=nRT

Example Question #12 : Gases And Gas Laws

A helium balloon has a volume of \displaystyle 735mL when it is at ground level. The balloon is transported to an elevation of \displaystyle 5km, where the pressure is only \displaystyle 0.8atm. At this altitude the gas occupies a volume of \displaystyle 1286mL. Assuming the temperature has remained the same, what was the ground level pressure?

Possible Answers:

\displaystyle 1.0atm

\displaystyle 1.4atm

\displaystyle 1.2atm

\displaystyle 0.7atm

Correct answer:

\displaystyle 1.4atm

Explanation:

To solve this question we will need to use Boyle's law:

\displaystyle P_1V_2=P_2V_2

We are given the final pressure and volume, along with the initial volume. Using these values, we can calculate the initial pressure.

\displaystyle P_1(735mL)=(0.8atm)(1286mL)

\displaystyle P_1=\frac{(0.8atm)(1286mL)}{735mL}

\displaystyle P_1=1.4atm

Note that the pressure at sea level is equal to \displaystyle 1.0atm. A pressure greater than \displaystyle 1.0atm simply indicates that the ground level is below sea level at this point.

Example Question #386 : High School Chemistry

The graph depicted here represents which of the gas laws?

Boyle_s_law_graph

Possible Answers:

Hund's law

Gay-Lussac's law

Charles's law

Boyle's law

Correct answer:

Boyle's law

Explanation:

The graph shows that there is an inverse relationship between the volume and pressure of a gas, when kept at a constant temperature. This was described by Robert Boyle and can be represented mathematically as Boyle's law:

\displaystyle P_1V_1=P_2V_2

Gay-Lussac's law shows the relationship between pressure and temperature. Charles's law shows the relationship between volume and temperature. Hund's rule (Hund's law) is not related to gases, and states that electron orbitals of an element will be filled with single electrons before any electrons will form pairs within a single orbital.

Example Question #14 : Gases And Gas Laws

A sample of oxygen gas has a volume of \displaystyle 225mL when its pressure is \displaystyle 1.12atm. What will the volume of the gas be at a pressure of \displaystyle 0.98atm if the temperature remains constant?

Possible Answers:

\displaystyle 250mL

\displaystyle 220mL

\displaystyle 316mL

\displaystyle 257mL

Correct answer:

\displaystyle 257mL

Explanation:

To solve this question we will need to use Boyle's law:

\displaystyle P_1V_2=P_2V_2

We are given the initial pressure and volume, along with the final pressure. Using these values, we can calculate the final volume.

\displaystyle (1.12atm)(225mL)=(0.98atm)V_2

\displaystyle V_2=\frac{(1.12atm)(225mL)}{0.98atm}

\displaystyle V_2=257mL

Example Question #1 : Using Boyle's Law

A gas is initially in a 5L piston with a pressure of 1atm.

If pressure changes to 3.5atm by moving the piston down, what is new volume?

Possible Answers:

\displaystyle 1.43 L

\displaystyle 1.75 L

\displaystyle 2.7 L

\displaystyle 1. 31 L

\displaystyle 2.03 L

Correct answer:

\displaystyle 1.43 L

Explanation:

Use Boyle's Law:

\displaystyle P_1*V_1 = P_2*V_2

Plug in known values and solve for final volume.

\displaystyle 5L+1atm=3.5atm*V_2

\displaystyle V_2=1.43L

Example Question #1 : Using Boyle's Law

A balloon of volume \displaystyle .666L at \displaystyle 1.03atm is placed in a pressure chamber where the pressure becomes \displaystyle 5.68atm, determine the new volume.

Possible Answers:

\displaystyle 1.27L

\displaystyle .467L

\displaystyle .121L

\displaystyle .033L

\displaystyle .236L

Correct answer:

\displaystyle .121L

Explanation:

Use Boyle's law and plug in appropriate parameters:

\displaystyle P_1V_1=P_2V_2

\displaystyle .666L*1.03atm=5.68atm*V_2

\displaystyle \frac{.666L*1.03atm}{5.68L}=V_2

\displaystyle .121L=V_2

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