Chapter 12 Section 1

Chapter 12 Section 1

Gases

The Kinetic-Molecular Theory

The kinetic-molecular theory describes the behavior of matter in terms of particles in motion.

Multiple Choice

When gas particle collide

• energy is lost

• explosions occur

• no energy is lost.

Kinetic Molecular Theory cont.

• Elastic collision -- one in which no kinetic energy is lost.

• Temperature -- a measure of the average kinetic energy of the particles in a sample of matter.

Explaining the Behavior of Gases

• The constant motion of gas particles allows a gas to expand and fill its container.

• Gases have very low density

• Gases can compress or expand.

Multiple Select

Gases

• have low density

• compress easily

• expand to fill a container

• are in constant motion.

Diffusion and Effusion

• Diffusion -- the random mixing of gases due to particle motion until they are evenly spread.

• Effusion -- the movement from an area of higher concentration to an area of lower concentration.

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Graham's Law

Graham's Law of effusion states that the rate of effusion for a gas is inversely proportional to the square root of its molar mass.

Multiple Choice

What is the molar mass of NH₃?

• 17.0 g/mol

• 15.00 g/mol

• 43.0 g/mol

Multiple Choice

What is the molar mass of HCl?

• 36.5 g/mol

• 46.0 g/mol

• 32.1 g/mol

Graham's Law

Ammonia has a molar mass of 17.0 g/mol; hydrogen chloride has a molar mass of 36.5 g/mol. What is the ratio of their diffusion rates? (Clue: the lower molar mass goes in the denominator position of the fraction.)

 $\frac{Rate_{NH_3}}{Rate_{HCl}}$  = $\sqrt{\frac{molar\ mass_{HCl}}{molar\ mass_{NH_3}}}$  

                     = $\sqrt{\frac{36.5g\div mol}{17.0g\div mol}}$  = 1.47
The ratio of diffusion is 1.47

Multiple Choice

Calculate the ratio of effusion rates for nitrogen gas (N2) with a molar mass of 28.0 g/mol and Ne gas with a molar mass of 20.2 g/mol.

 $\frac{Rate\ Ne}{Rate\ N_2}$  =  $\sqrt{\frac{molar\ mass\ N_2}{molar\ mass\ Ne}}$  

• 1.17

• 0.849

• 2.31

Gas Pressure

Pressure is defined as force per unit area.

Measuring Air Pressure

A barometer is an instrument used to measure atmospheric pressure.

Measuring Air Pressure cont.

A manometer is an instrument used to measure gas pressure in a closed container.

Units of Pressure

The SI unit of pressure is the pascal (Pa). One pascal is equal to a force of one newton per square meter: 1 Pa = 1 N/m²

Typically, air pressure is measured in atmospheres in chemistry.

Multiple Select

One atmosphere equals

• 760 mm Hg

• 760 torr

• 14.7 psi

• 101,325 Pa

• 101.3 kPa

Dalton's Law of Partial Pressures

Dalton's law of partial pressures states that the total pressure of a mixture of gases is equal to the sum of the pressures of all the gases in the mixture.

The Partial Pressure of a Gas

A mixture of oxygen (O₂), carbon dioxide (CO₂), and nitrogen (N₂) has a total pressure of 0.97 atm. What is the partial pressure of O₂ if the partial pressure of CO₂ is 0.70 atm and the partial pressure of N₂ is 0.12 atm?

P_total = P₁ + P₂ + P₃

P_total = P_O2 + P_CO2 + P_N2

P_O2 = P_total - P_CO2 - P_N2

P_O2 = 0.97 atm - 0.70 atm - 0.12 atm

P_O2 = 0.15 atm

Multiple Choice

What is the partial pressure of hydrogen gas (H₂) in a mixture of hydrogen and helium (He) if the total pressure is 600 mmHg and the partial pressure of helium is 439 mmHg? P_total = P_H2 + P_He

• 1039 mmHg

• 600 mmHg

• 161 mmHg

• 439 mmHg

End