Gas Laws Examples in Chemistry

Start with the recap, study the fully worked examples, then use the practice problems to check your understanding of Gas Laws.

This page combines explanation, solved examples, and follow-up practice so you can move from recognition to confident problem-solving in Chemistry.

Concept Recap

A set of mathematical relationships that describe how the pressure, volume, temperature, and amount (moles) of a gas are interconnected.

How gases behave when you squeeze them, heat them, or add more.

Read the full concept explanation →

How to Use These Examples

  • Read the first worked example with the solution open so the structure is clear.
  • Try the practice problems before revealing each solution.
  • Use the related concepts and background knowledge badges if you feel stuck.

What to Focus On

Core idea: Gas Laws starts by listing pressure, volume, temperature, amount, and which are held constant.

Common stuck point: Students often know a formula related to gas laws but skip the recognition step: Am I comparing gas variables with units and temperature in kelvin, while holding the stated variables constant? That leads to a correct-looking substitution attached to the wrong chemical model.

Sense of Study hint: Ask: Am I comparing gas variables with units and temperature in kelvin, while holding the stated variables constant?

Worked Examples

Example 1

easy
A gas occupies 2.0 L2.0\,\text{L} at 1.0 atm1.0\,\text{atm}. What is its volume at 3.0 atm3.0\,\text{atm} (constant temperature)?

Answer

V2=0.67 LV_2 = 0.67\,\text{L}

First step

1
Use Boyle's Law: P1V1=P2V2P_1V_1 = P_2V_2.

Full solution

  1. 2
    1.0×2.0=3.0×V21.0 \times 2.0 = 3.0 \times V_2.
  2. 3
    V2=2.03.0=0.67 LV_2 = \frac{2.0}{3.0} = 0.67\,\text{L}.
Boyle's Law states that pressure and volume are inversely proportional at constant temperature. Tripling the pressure reduces the volume to one-third.

Example 2

medium
Use the ideal gas law to find the volume occupied by 2.02.0 mol of gas at 25°C25°\text{C} and 1.0 atm1.0\,\text{atm}. (R=0.0821 L\cdotpatm/mol\cdotpKR = 0.0821\,\text{L·atm/mol·K})

Example 3

medium
A 1.51.5-mol sample of N2_2 occupies what volume at 0.900.90 atm and 350350 K? (R=0.0821R = 0.0821)

Example 4

medium
A 0.2500.250-mol sample of an ideal gas occupies 5.005.00 L at 295295 K. Find its pressure in atm. (R=0.0821R = 0.0821)

Example 5

medium
A 10.010.0-L container has 0.200.20 mol He and 0.300.30 mol Ne at 300300 K. Find the total pressure. (R=0.0821R = 0.0821)

Example 6

hard
A 2.002.00-L flask contains 0.5000.500 mol N2_2 and 0.3000.300 mol O2_2 at 400400 K. Find the partial pressure of O2_2. (R=0.0821R=0.0821)

Example 7

challenge
Two gases He and Ne are at the same temperature. What is the ratio of their average molecular speeds, vHe/vNev_{He}/v_{Ne}? (MHe=4M_{He}=4, MNe=20M_{Ne}=20)

Practice Problems

Try these problems on your own first, then open the solution to compare your method.

Example 1

easy
A gas at 200 K200\,\text{K} occupies 4.0 L4.0\,\text{L}. What volume does it occupy at 400 K400\,\text{K} (constant pressure)?

Example 2

medium
A gas occupies 2.402.40 L at 1.001.00 atm. If the pressure increases to 1.501.50 atm at constant temperature, what is the new volume?

Example 3

easy
Convert 27 degrees C to Kelvin for a gas law calculation.

Example 4

easy
In PV = nRT, which variable is the pressure?

Example 5

easy
Using PV = nRT with n=1, R=0.0821, T=300 K, V=24.63 L, find P (in atm).

Example 6

easy
At constant pressure and amount, if temperature increases, what happens to gas volume (Charles's law)?

Example 7

easy
Do gas laws apply to liquids and solids?

Example 8

easy
At constant temperature and amount, if volume decreases, what happens to pressure (Boyle's law)?

Example 9

easy
What temperature scale must be used in all gas law equations?

Example 10

easy
At constant T and P, if you double the moles of gas, what happens to the volume (Avogadro's law)?

Example 11

medium
A gas at 2 atm and 300 K is heated to 600 K at constant volume. Find the new pressure (Gay-Lussac's law).

Example 12

medium
A gas occupies 4 L at 200 K. At constant pressure, what volume does it occupy at 300 K (Charles's law)?

Example 13

medium
Find the moles of an ideal gas at P=2 atm, V=10 L, T=300 K (R=0.0821).

Example 14

medium
A gas at STP (1 atm, 273 K) occupies 22.4 L per mole. How many liters do 2 mol occupy at STP?

Example 15

medium
A gas occupies 5 L at 300 K and 1 atm. Find its volume at 600 K and 2 atm (combined gas law).

Example 16

medium
How many grams of O2 (molar mass 32) are in 11.2 L at STP (22.4 L/mol)?

Example 17

medium
A 0.5 mol gas sample is at 4 atm and 400 K. Find its volume (R=0.0821).

Example 18

medium
A gas at 5 atm in 3 L expands to 15 L at constant temperature. Find the new pressure (Boyle's law).

Example 19

medium
A gas occupies 10 L at 250 K. At constant pressure, find its volume at 500 K (Charles's law).

Example 20

challenge
A gas occupies 3 L at 1 atm and 300 K. It is compressed to 1 L and heated to 400 K. Find the new pressure.

Example 21

challenge
What is the density of CO2 (molar mass 44) at STP, using molar volume 22.4 L/mol?

Example 22

challenge
A 2 L vessel holds 0.1 mol N2 and 0.1 mol O2 at 300 K. Find the total pressure (R=0.0821, Dalton's law).

Example 23

easy
A gas occupies 6.06.0 L at 2.02.0 atm. At constant temperature, what volume does it occupy at 4.04.0 atm?

Example 24

easy
A balloon at 300 K300\,\text{K} has volume 2.0 L2.0\,\text{L}. At constant pressure, what volume at 600 K600\,\text{K}?

Example 25

easy
At constant T, V, if moles of gas double, what happens to pressure?

Example 26

easy
How many moles of gas occupy 11.211.2 L at STP (22.422.4 L/mol)?

Example 27

medium
A weather balloon holds 5.005.00 L at 1.001.00 atm and 290290 K. At altitude, conditions become 0.500.50 atm and 260260 K. Find the new volume.

Example 28

medium
A rigid tank holds gas at 3.03.0 atm and 300300 K. The tank is heated to 450450 K. Find the new pressure.

Example 29

medium
How many grams of CO2_2 (M=44.0M = 44.0) are in a 5.005.00-L cylinder at 2.002.00 atm and 300300 K? (R=0.0821R = 0.0821)

Example 30

medium
A flexible balloon at 25 °C25\,°\text{C} contains 4.04.0 L of air. It is placed in liquid nitrogen at 77 K77\,\text{K}. Estimate the new volume (constant pressure).

Example 31

medium
A sample of unknown gas weighs 4.404.40 g and occupies 2.242.24 L at STP. Find its molar mass.

Example 32

medium
A gas at 1.501.50 atm in 4.004.00 L is compressed to 2.002.00 L at constant T. Find the new pressure.

Example 33

medium
At 0 °C0\,°\text{C} and 1.01.0 atm, a balloon holds 5.005.00 L. Find its volume at 30 °C30\,°\text{C} and 1.01.0 atm.

Example 34

hard
A 2.502.50-g sample of an unknown gas occupies 1.501.50 L at 1.201.20 atm and 310310 K. Find the molar mass. (R=0.0821R = 0.0821)

Example 35

hard
In the reaction Zn+2HCl→ZnCl2+H2\text{Zn} + 2\text{HCl} \rightarrow \text{ZnCl}_2 + \text{H}_2, 0.6540.654 g Zn (M=65.4M=65.4) reacts. What volume of H2_2 is produced at STP?

Example 36

hard
A gas at 2.02.0 atm, 300300 K is compressed to half its volume and cooled to 250250 K. Find the new pressure.

Example 37

hard
Find the density of N2_2 (M=28.0M=28.0) at 1.001.00 atm and 298298 K. (R=0.0821R=0.0821)

Example 38

hard
How many liters of O2_2 at 1.001.00 atm and 298298 K are needed to burn 16.016.0 g CH4_4 (M=16.0M=16.0)? Reaction: CH4+2O2→CO2+2H2O\text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O}. (R=0.0821R=0.0821)

Example 39

hard
A scuba tank holds 12.012.0 L of air at 200200 atm and 300300 K. If released to 1.001.00 atm at 300300 K, what total volume of air is available?

Example 40

challenge
Hydrogen gas is collected over water at 25 °C25\,°\text{C} and 755755 mmHg total pressure. The vapor pressure of water at 25 °C25\,°\text{C} is 2424 mmHg. Find the partial pressure of H2_2.
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Background Knowledge

These ideas may be useful before you work through the harder examples.

moleparticle theory