AP Chemistry : AP Chemistry

Study concepts, example questions & explanations for AP Chemistry

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Example Questions

Example Question #901 : Ap Chemistry

In reality, the volume of a gas is slightly larger than the ideal volume. This is because __________.

Possible Answers:

ideal volume already uses the volume of the gas molecules

ideal volume does not incorporate pressure's effect on the size of the container

ideal volume does not take the width of the container into consideration

ideal volume does not take the volume of the gas molecules into consideration

Correct answer:

ideal volume does not take the volume of the gas molecules into consideration

Explanation:

One of the key charactersitics of an ideal gas is that gas molecules have no volume. This is obviously not the case, and the volume of the molecules must be added to the ideal volume. As a result, the real volume is slightly larger than the ideal volume. 

Example Question #901 : Ap Chemistry

Which of the following conditions would cause a gas to act the most like an ideal gas?

Possible Answers:

High pressure and high temperature

Low volume and low temperature

Low pressure and low temperature

High pressure and high temperature

Low pressure and high temperature

Correct answer:

Low pressure and high temperature

Explanation:

An ideal gas acts as if there are no interactions between the gaseous molecules during their rapid movements. At high temperature and low pressure the particles of the gas will not interact very much, as they will have high energy and will move around very fast. The faster the movement, the less time and contact the particles have with one another. The slower the particles are moving, the more they are starting to act like a liquid, and less like an ideal gas. High pressure will condense the particles, while low pressure will allow them to move freely. High temperature will add energy to speed the particles, while low temperature will slow them down.

Example Question #8 : Solids, Liquids, And Gases

You place some balloons in your car, and leave them to sit as the car is heated by the sun. What effect would this have on the gases inside the helium balloons?

Assume the balloons are fully elastic.

Possible Answers:

The volume of the balloons will increase

There will be more molecules of helium inside the balloons

The temperature of the gases surrounding the balloon will decrease

The volume of the balloons will decrease

The pressure inside the balloons will increase

Correct answer:

The volume of the balloons will increase

Explanation:

We can predict the result of the heating by using the ideal gas law:

We know that , which is a constant, will never change. We also know that , the number of moles of helium inside the balloons, will stay the same since no gas is added or removed from the sealed balloons.

The variables in this case are pressure, volume, and temperature. We know that the temperature will increase because the sun is heating up the car. This leaves us with pressure and volume. Pressure will not increase because the balloons are elastic; as the gas expands, the balloons expand as well without increasing the pressure. In this scenario, only the volume will increase.

Example Question #902 : Ap Chemistry

Which of the following conditions would result in the deviation of a gas from ideality?

Possible Answers:

A gas would behave ideally regardless of temperature and pressure

Low temperature and high pressure

High temperature and low pressure

Low temperature and low pressure

High temperature and high pressure

Correct answer:

Low temperature and high pressure

Explanation:

Under high pressure, the volume of the gas molecules would no longer be negligible—one of the assumptions for an ideal gas. In addition, at low temperature, the molecules would have less kinetic energy, and intermolecular forces could take affect—another assumption of an ideal gas is that there are no intermolecular attractions or repulsions.

At low pressure and high temperature, gases behave more like gases and liquids are more likely to boil (convert to gas). At high pressure and low temperature, gases behave less ideally and can condense (convert to liquid).

Example Question #903 : Ap Chemistry

Hydrogen gas is being stored in a container. The pressure of the gas is suddenly doubled. What could NOT be an explanation for this sudden change?

Possible Answers:

A laboratory assistant thought it was warm in the lab, so he turned on the air conditioning system.

A lab assistant squeezed the container into a storage closet, in order to make it fit.

A lab assistant accidentally turned a nozzle, allowing more hydrogen gas to enter the container.

A lab assistant left a bunsen burner on near the container, causing it to warm up.

Correct answer:

A laboratory assistant thought it was warm in the lab, so he turned on the air conditioning system.

Explanation:

When dealing with gas problems that have multiple factors but very little data is given, it is a good idea to use the ideal gas law to compare factors.

The ideal gas law is written as PV = nRT

This allows us to see how factors could affect the pressure in the container. By lowering volume, we would see that pressure increased. If more gas was allowed into the container (increasing n), the pressure would increase as well. If we lower the temperature (lower T), then pressure should decrease as well. As a result, pressure rising due to a drop in temperature does not make sense in this question.

Example Question #1 : Phases Of Matter

If you create a perfect vacuum and place a glass of water into the vacuum at room temperature, what will happen to the water?

Possible Answers:

The water will float about the vacuum

The water will boil

The water will boil very rapidly and then stop

Nothing will happen

The water will freeze

Correct answer:

The water will boil

Explanation:

Boiling occurs when the vapor pressure exceeds the air pressure. There is no air pressure in a vacuum, so water at any temperature will boil in a vacuum.

Example Question #2 : Solids And Liquids

Boiling points at standard temperature and pressure:

Methanol-

Toluene-

Water-

Methylene chloride-

Dimethylsulfoxide-

Of the five compounds given, which will have the highest vapor pressure at standard temperature and pressure?

Possible Answers:

Water

Toluene

Methylene chloride

Methanol

Dimethylsulfoxide

Correct answer:

Methylene chloride

Explanation:

A liquid will boil when its vapor pressure increases to match the pressure of its environment. By this logic, a liquid with a higher vapor pressure will be closer to boiling. Liquids with low boiling points thus have greater vapor pressures.

Of the given compounds, methylene chloride has the lowest boiling point, meaning it will also have the highest vapor pressure.

Example Question #131 : Solutions And States Of Matter

Oil and vinegar is a very popular salad dressing. It also is commonly used for dipping bread. The main component of the oil phase is olive oil, while the main part of the vinegar portion is aqueous acetic acid.

When oil and vinegar salad dressing is allowed to stand at room temperature, two distinct phases are observed. The main explanation for this phenomenon is the difference in _________ of the two phases.

Possible Answers:

solubility

buoyancy

polarity

density

acidity

Correct answer:

polarity

Explanation:

Olive oil, like most oils, is non-polar, while aqueous acetic acid is very polar. These two phases do not mix because of their different solvent polarities.

Example Question #1 : Ideal Gas Law

What is the final pressure of a gas initially has a pressure of 10 atm at 50 L if the volume s now 25 L?

Possible Answers:

20 atm

50 atm

5 atm

10 atm

25 atm

Correct answer:

20 atm

Explanation:

Use P1V1 = P2V2

P1 = 10atm; V1 = 50L

P2 = X; V2 = 25L

(10atm)(50L) = (x)(25L)

500 = 25x

x = 20

Example Question #1 : Ideal Gas Law

A sample of ideal gas is heated in a 2L vessel at a temperature of 320 Kelvin. The pressure in the vessel is 2.5atm. What is the new pressure in the vessel if the volume is halved and the temperature is reduced to 250 Kelvin?

Possible Answers:

Correct answer:

Explanation:

Since the gas is ideal, we can use a variation of the ideal gas law in order to find the unknown final pressure.

Since we know that the number of moles is constant between both vessels (and R is a constant as well), we can simply compare the three factors being manipulated between the two vessels: pressure, volume, and temperature. Using a combination of Boyle's law and Charles's law, we can compare the two vessels to one another using the following equation.

Use the given values to solve for the final pressure.

 

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