Q: A mixture contains equal numbers of moles of He and Ne. The total pressure of the mixture is $$3.0 \text{ atm}. $$What are the partial pressures of He and Ne?

$$1.5 \text{ atm}$$ for He and $$1.5 \text{ atm}$$ for Ne

Q: According to Graham’s law, what is the ratio of the rates of effusion of two gases at the same temperature?

$$\dfrac{\text{rate}_1}{\text{rate}_2} = \sqrt{\dfrac{M_2$}{M_1$}}$$

Question 1

Which of the following best explains why atmospheric pressure decreases with increasing altitude?

Accepted Answer

The number of gas particles per unit volume decreases as altitude increases.

Question 2

A diver descends to a depth of 20 meters in the ocean. If the pressure at the surface is 1 atm, what is the total pressure experienced by the diver at this depth?

Accepted Answer

$$3 	ext{ atm}$$

Question 3

Which instrument is used to measure the pressure of a gas trapped in a container, and how does it work?

Accepted Answer

A manometer; it compares the pressure of the gas to atmospheric pressure using the difference in liquid levels.

Question 4

According to Boyle’s Law, if the pressure on a gas sample is tripled at constant temperature, what happens to its volume?

Accepted Answer

The volume decreases to one-third of its original value.

Question 5

A balloon is moved from an ice water bath ($$0^\circ 	ext{C}) to a $$boiling water bath ($$100^\circ 	ext{C}) at $$constant pressure. What happens to the volume of the balloon?

Accepted Answer

The volume increases because the gas particles move faster and occupy more space.

Question 6

Which of the following actions will increase the volume of a gas sample?

Accepted Answer

Decreasing the pressure at constant temperature and number of moles.

Question 7

At STP, which of the following samples has the greatest volume?

Accepted Answer

All have the same volume if they contain 1 mole of gas.

Question 8

What is the density of nitrogen gas ($$	ext{N}_2) at $$STP?

Accepted Answer

$$1.25 	ext{ g/L}$$

Question 9

A mixture contains equal numbers of moles of He and Ne. The total pressure of the mixture is $$3.0 	ext{ atm}. $$What are the partial pressures of He and Ne?

Accepted Answer

$$1.5 	ext{ atm}$$ for He and $$1.5 	ext{ atm}$$ for Ne

Question 10

A gas is collected over water at $$25^\circ 	ext{C}$$ and the total pressure is $$758.2 	ext{ mmHg}. If $$the vapor pressure of water at this temperature is $$23.7 	ext{ mmHg}$$, what is the partial pressure of the dry gas?

Accepted Answer

$$734.5 	ext{ mmHg}$$

Question 11

Which postulate of the kinetic molecular theory explains why gases are compressible?

Accepted Answer

There is a lot of empty space between gas particles compared to their size.

Question 12

Which of the following statements about molecular velocities is correct?

Accepted Answer

At the same temperature, lighter gas molecules have higher average velocities than heavier ones.

Question 13

According to Graham’s law, what is the ratio of the rates of effusion of two gases at the same temperature?

Accepted Answer

$$\dfrac{	ext{rate}_1}{	ext{rate}_2} = \sqrt{\dfrac{M_2$}{M_1$}}$$

Question 14

Which modification to the ideal gas law accounts for the finite volume of gas particles?

Accepted Answer

The van der Waals constant $$b is $$added to the volume term: $$V - nb$$

Question 15

At low temperatures, real gases deviate from ideal behavior primarily because:

Accepted Answer

Intermolecular attractions cause the pressure to be lower than predicted.

Question 16

Which of the following equations represents the van der Waals equation for real gases?

Accepted Answer

$$\left[P + a \left(\dfrac{n}{V}\$$right)^2$$ \right] (V - nb) = nRT$$

Question 17

A sample of gas at constant volume undergoes a chemical reaction that decreases the total number of moles of gas. What happens to the pressure?

Accepted Answer

The pressure decreases.

Question 18

If the root mean square velocity of Ne is compared to that of Kr at the same temperature, what is true?

Accepted Answer

The root mean square velocity of Ne is approximately twice that of Kr.

Question 19

Which of the following best describes the relationship between pressure and density for a gas at constant temperature?

Accepted Answer

Pressure is directly proportional to density.

Chapter 6: Gases – Properties, Laws, and Molecular Theory

Guida di studio - Domande di pratica

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