Boyles and Charles Law

Boyles and Charles Law

High School

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Learning Objectives

• Explain how a gas's volume and pressure are related at a constant temperature.

• Describe how a gas's volume and temperature are related at a constant pressure.

• Use the kinetic molecular theory to explain the behavior of gases.

• Use Boyle's Law and Charles's Law to solve for unknown variables.

Key Vocabulary

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Boyle's Law

Describes the inverse relationship between the pressure and volume of a gas at constant temperature.

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Charles's Law

Describes the direct relationship between the volume and temperature of a gas at constant pressure.

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Pressure

The amount of force exerted by gas particles as they collide with their container's walls.

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Kelvin Scale

A temperature scale where zero represents absolute zero, used for all gas law calculations.

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Boyle's Law: Pressure and Volume

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Solved Example 1
A 150.0 mL sample of oxygen gas has a pressure of 0.947 atm. What is the new volume if the pressure increases to 0.987 atm, assuming the temperature remains constant?

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Step 1: Analyze and Sketch the Problem

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Solved Example 1
A 150.0 mL sample of oxygen gas has a pressure of 0.947 atm. What is the new volume if the pressure increases to 0.987 atm, assuming the temperature remains constant?

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Step 2: Solve for the Unknown

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Solved Example 1
A 150.0 mL sample of oxygen gas has a pressure of 0.947 atm. What is the new volume if the pressure increases to 0.987 atm, assuming the temperature remains constant?

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Step 3: Evaluate the Answer

• According to Boyle's law, as pressure increases, volume should decrease.

• The pressure increased from 0.947 atm to 0.987 atm, and the volume decreased from 150.0 mL to 144.0 mL. This is consistent with the law, and the answer is reasonable.

Multiple Choice

A sealed container of gas is kept at a constant temperature. If the volume of the container is doubled, what happens to the pressure of the gas according to Boyle's Law?

• The pressure is doubled.

• The pressure is reduced by half.

• The pressure is quadrupled.

• The pressure remains the same.

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Charles's Law: Volume and Temperature

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Solved Example 2
A 4.0 L sample of gas is at 20°C. If the temperature is increased to 40°C at constant pressure, what will the new volume of the gas be?

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Step 1: Analyze and Sketch the Problem

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Solved Example 2
A 4.0 L sample of gas is at 20°C. If the temperature is increased to 40°C at constant pressure, what will the new volume of the gas be?

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Step 2: Solve for the Unknown

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Solved Example 2
A 4.0 L sample of gas is at 20°C. If the temperature is increased to 40°C at constant pressure, what will the new volume of the gas be?

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Step 3: Evaluate the Answer

• According to Charles's Law, volume should increase as temperature increases. The temperature increased from 293 K to 313 K, and the volume increased from 4.0 L to 4.27 L.

• The result is logical and the unit (L) is correct for volume.

Multiple Choice

According to Charles's Law, what is the primary reason for converting temperature measurements from Celsius to Kelvin before using the formula V₁/T₁ = V₂/T₂?

• The Kelvin scale is directly proportional to volume, while the Celsius scale is not.

• The calculations are simpler with Kelvin.

• Kelvin is a more precise unit than Celsius.

• It is a scientific convention with no mathematical reason.

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Common Misconceptions about Gas Laws

Misconception	Correction
You can use Celsius for Charles's Law.	Temperatures must be in Kelvin for Charles's Law to apply.
Pressure and volume are directly related.	Boyle's Law shows they are inversely related at constant temperature.
The gas laws apply under all conditions.	Boyle's Law requires constant temperature, and Charles's Law constant pressure.

Multiple Choice

If a diver releases a bubble of air at a deep depth and it rises to the surface, how does its volume change and which law explains this? (Assume temperature is constant).

• It expands; Boyle's Law

• It expands; Charles's Law

• It shrinks; Charles's Law

• It shrinks; Boyle's Law

Multiple Choice

A car tire's pressure is related to the temperature of the air inside. Why might a tire that seems fine on a hot afternoon look underinflated on a cold morning, based on the principles of the gas laws?

• The air molecules shrink in the cold, which is described by Boyle's Law.

• The tire's rubber becomes stiffer in the cold, squeezing the air.

• The air molecules move slower and exert less pressure at lower temperatures, a principle related to Charles's Law.

• Some of the air must have leaked out overnight due to the cold.

Multiple Choice

A scientist has a 500 mL sample of gas at 1 atm and 25°C. To what pressure must the gas be subjected to reduce the volume to 250 mL, assuming the temperature remains constant?

• 1.5 atm

• 0.25 atm

• 2 atm

• 0.5 atm

Multiple Choice

A hot air balloon has a volume of 5.5 L at 25°C. To what temperature must it be heated to expand to a volume of 11 L, assuming constant pressure?

• 298 K

• 100°C

• 50°C

• 596 K

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Summary

Poll

On a scale of 1-4, how confident are you with applying Boyle's and Charles's Laws?

• 1

• 2

• 3

• 4