The Ideal Gas Law Lesson 2

The Ideal Gas Law

Lesson 2

Focus Question

What happens when you change the
amount of gas present?

New Vocabulary

Avogadro’s principle

molar volume

standard temperature and pressure (STP)

ideal gas constant (R)

ideal gas law

Review Vocabulary

mole: an SI base unit used to measure the amount
of a substance; the amount of a pure substance that
contains 6.02 × 10²³ representative particles

Avogadro’s Principle

Avogadro’s principle states that equal volumes of
gases at the same temperature and pressure
contain equal numbers of particles.
• The figure shows equal volumes of carbon

dioxide, helium, and oxygen.

Multiple Choice

What does Avogadro's principle state?

• Equal volumes of gases at different temperatures contain equal numbers of particles.

• Equal volumes of gases at different pressures contain equal numbers of particles.

• Equal volumes of gases at the same temperature and pressure contain equal numbers of particles.

• Equal volumes of gases at the same temperature contain equal numbers of particles.

Avogadro’s Principle

Volume and Moles
• The molar volume of a gas is the volume 1 mol

occupies at 0.00°C and 1.00 atm of pressure.

• 0.00°C and 1.00 atm are called standard

temperature and pressure (STP).

• At STP, 1 mol of gas occupies 22.4 L.

Multiple Choice

What are the values for standard temperature and pressure (STP)?

• 
  $$0.00\ \degree C\ and\ 1.00\ atm$$

• $$25.0\ \degree C\ and\ 0.00\ atm$$

• $$273\ \degree C\ and\ 1.00\ atm$$

• $$1.00\ \degree C\ and\ 0.00\ atm$$

Multiple Choice

What is the molar volume of a gas at standard temperature and pressure (STP)?

• 1 L

• 22.4 L

• 0.0821 L

• 6.02 × 10^-23 L

The Ideal Gas Law

• The ideal gas constant is represented by R

and is 0.0821 L•atm/mol•K when pressure is
in atmospheres.

• The ideal gas law describes the physical

behavior of an ideal gas in terms of the
pressure, volume, temperature, and number
of moles of gas present.

PV = nRT

• For a given amount of gas held at constant

temperature, the product of pressure and
volume is a constant.

Multiple Choice

What is the ideal gas constant (R) when pressure is in atmospheres?

• 0.0821 L•atm/mol•K

• 22.4 L

• 1 L

• 6.02 × 10^-23 L

Multiple Choice

Which equation represents the ideal gas law?

• PV = nRT

• PT = nRV

• PV = RT/n

• PT = RV/n

The Ideal Gas Law—Molar Mass and Density

The PV = nRT equation can be rearranged to
calculate the molar mass of a gas sample.

Multiple Choice

How can the molar mass of a gas sample be calculated using the ideal gas law?

• By rearranging the equation PV = nRT

• By rearranging the equation PV = nRT and substituting the values of pressure, volume, and temperature

• By rearranging the equation PV = nRT and substituting the values of pressure, volume, and number of moles

• By rearranging the equation PV = nRT and substituting the values of volume, temperature, and number of moles

The Ideal Gas Law—Molar Mass and Density

The PV = nRT equation can be rearranged to
calculate the density of a gas sample.

Real Versus Ideal Gases

• Ideal gases follow the assumptions of the

kinetic-molecular theory.

• Characteristics of ideal gases:

• Their particles take up no space.
• There are no intermolecular attractive

or repulsive forces between particles or
with their containers.

• The particles are in constant random

motion.

• Collisions are perfectly elastic.

Real Versus Ideal Gases

• No gas is truly ideal, but most behave as

ideal gases at a wide range of
temperatures and pressures.

• All gas particles have some volume,

however small, and are subject to
intermolecular interactions.

• The collisions that particles make with

each other and with the container are not
perfectly elastic.

• Most gases behave like ideal gases at a

wide range of temperatures and pressures.

Multiple Choice

What is the main difference between ideal gases and real gases?

• Ideal gases have no intermolecular forces, while real gases do.

• Ideal gases have larger attractive forces between particles, while real gases do not.

• Ideal gases have no volume, while real gases do.

• Ideal gases have perfectly elastic collisions, while real gases do not.

Real Versus Ideal Gases

• Real gases deviate most from ideal gas

behavior at high pressures and low
temperatures.

Polarity and Size of Particles
• Polar molecules have larger attractive forces

between particles.

• Polar gases do not behave as ideal gases.
• Large nonpolar gas particles occupy more

space and deviate more from ideal gases.

Extreme Pressure and Temperature

Multiple Choice

Which assumption is not followed by ideal gases?

• Gas particles are in constant, random motion.

• Gas particles take up no space.

• Gas particles have no intermolecular forces.

• Gas particle collisions are perfectly elastic.

Multiple Choice

At what conditions do real gases deviate most from ideal gas behavior?

• High pressures and high temperatures

• Low pressures and low temperatures

• High pressures and low temperatures

• Low pressures and high temperatures

Multiple Choice

Which type of gas particles deviate more from ideal gas behavior?

• Small nonpolar particles

• Large nonpolar particles

• Small polar particles

• Large polar particles