Exam (elaborations) GIZMOS Pierra Flack Gizmo Equilibrium and Pressure Guaranteed A+: Latest 2023:2024

2019

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Student Exploration: Equilibrium and Pressure

[Note to teachers and students: This Gizmo was designed as a follow-up to the Equilibrium and

Concentration Gizmo. We recommend doing that activity before trying this one.]

Vocabulary: Dalton’s law, Le Châtelier’s principle, partial pressure, pressure

Prior Knowledge Questions (Do these BEFORE using the Gizmo.)

A typical scuba tank has a volume of 11 liters and can support a diver for one

hour. An adult breathes about 3 liters of air with each breath.

1. How can an 11-liter tank give a diver enough oxygen for one hour? The

deeper you go the more pressure the diver’s lung are

under. The added pressure means less air is required

for respiration.

2. Why are diving cylinders made of thick, reinforced aluminum or steel? To

withstand the pressure exerted by the water the

deeper they go down.

Gizmo Warm-up

Gases consist of billions of tiny particles in constant motion,

colliding with each other and the walls of the container. The sum of

all these collisions creates pressure on the walls of the container.

In theory, any amount of gas can be squeezed into a container if the

container is strong enough to withstand the gas pressure.

The Equilibrium and Pressure Gizmo shows a mixture of gases in a

chamber. The lid of the chamber can move up or down.

1. Check that Reaction 1 is selected. Use the Moles NO2 slider to increase the number of NO2

molecules in the chamber. How does this affect the volume of the chamber? As NO2

increases, the volume of fluid in the container increases so the

volume of the chamber increases also and vice versa.

2. Notice the weights on the lower right side of the Gizmo. Drag several of these weights to

the lid. How does this affect the volume of the chamber? Added pressure

decreases the volume of the chamber.

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GIZMOS Pierra Flack Gizmo

Equilibrium and Pressure

2019

Activity A:

Dalton’s law

Get the Gizmo ready:

 Remove all weights from the lid.

 Set Moles NO2 and Moles N2O4 to 0.

Introduction: In a mixture of gases, each gas contributes a partial pressure to the total

pressure in the chamber. Because the chamber has a moveable piston, the pressure inside is

equal to the pressure on the lid. In this Gizmo, the units of pressure are megapascals (MPa).

Question: How do individual gases contribute to the total pressure in a chamber?

1. Observe: Set Moles NO2 to 2 to add 2 moles of NO2 gas to the chamber.

A. The total pressure (P) on the chamber is shown next to the weights, at bottom right.

What is the total pressure in the chamber? 54 MPa

B. Select the BAR CHART tab and select Pressure. Turn on Show data values.

What is the pressure of NO2? PNO2 = 54.00 MPa

2. Observe: Set Moles N2O4 to 2 to add 2 moles of N2O4 gas to the chamber.

A. What is the total pressure on the chamber? 54 MPa

B. What are the partial pressures of NO2 and N2O4? PNO2 = 27 MPa PN2O4 = 27

MPa

C. What is the sum of the partial pressures of NO2 and N2O4? 54 MPa

Dalton’s law states that the total pressure in a container is equal to the sum of the partial

pressures: P = P1 + P2 + …. + Pn

3. Explain: Why doesn’t the total pressure increase when more gas is added to the chamber?

(Hint: What would you see if the volume of the chamber was fixed?) As more gas is

added to the chamber and the chamber is at a fixed volume,

the gas molecules would be closer together, exerting more

pressure upon each other and the chamber.

4. Analyze: A molecule of N2O4 has twice the mass as a molecule of NO2. What do you notice

about the partial pressure exerted by 2 moles of NO2 compared to the partial pressure

exerted by 2 moles of N2O4? They are equal.

At a given temperature, the partial pressure exerted by a gas depends only on the quantity

of the gas, not on its mass. Thus a mole of a light gas such as hydrogen (H2) exerts the

same pressure as a mole of a heavier gas such as dinitrogen tetroxide (N2O4).

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