AP Chemistry : Kinetic Molecular Theory

Study concepts, example questions & explanations for AP Chemistry

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Example Questions

Example Question #1 : Kinetic Molecular Theory

Two moles of nitrogen gas are kept in a glass container. The temperature of the gas is 400K.

What is the kinetic energy of the gas?

Possible Answers:

Correct answer:

Explanation:

Using the equation , n being the number of moles, R being 8.314, and T being the temperature in Kelvin, we can find the kinetic energy of two moles of gas in a container.

Example Question #2 : Kinetic Molecular Theory

Which of the following is not an assumption of the kinetic molecular theory of gases?

Possible Answers:

The kinetic energy of gas particles are different for all gases at a certain temperature

Gas particles do not experience attractions/repulsions to other particles

Gas particles are in random, continuous motion

The volumes of the particles of a gas are negligible

Collisions between gas particles are elastic

Correct answer:

The kinetic energy of gas particles are different for all gases at a certain temperature

Explanation:

The kinetic molecular theory of gases states that the average kinetic energy of gas particles is proportional to temperature, and it is the same for all gases at a given temperature. This is the opposite of what is stated in the answer choice.

Example Question #3 : Kinetic Molecular Theory

Why does a higher temperature result in a faster reaction?

Possible Answers:

It lowers the activation energy for a reaction

It increases the surface area for reactions

It increases the number of effective molecular collisions

It increases the pressure of the reactants

It helps orient reactants into the correct position to react

Correct answer:

It increases the number of effective molecular collisions

Explanation:

The temperature of a system can be manipulated to increase the reaction rate. The temperature affects the rate of the reaction because as temperature increases, so does the average kinetic energy. This means that molecules (reactants) are moving around more quickly, resulting in more frequent molecular collisions, resulting in an increased rate of product formation.

Example Question #4 : Kinetic Molecular Theory

Which of the following statements in not an assumption made in kinetic molecular theory?

Possible Answers:

Much of the volume of the container is empty space

The average kinetic energy of gas molecules is a function of both temperature and pressure

No attractive forces exist between gas molecules

Collisions between gas molecules and the container are perfectly elastic

Correct answer:

The average kinetic energy of gas molecules is a function of both temperature and pressure

Explanation:

The average kinetic energy is considered to be a sole function of temperature; pressure is not a factor. All of the other statements are assumptions of kinetic molecular theory. 

Example Question #5 : Kinetic Molecular Theory

The reaction  obeys the rate law 

What are the units of the rate constant, ?

Possible Answers:

Correct answer:

Explanation:

Recall that  and that  and  are both molar concentrations. Then,

Dividing both sides by  gives

Example Question #6 : Kinetic Molecular Theory

Consider the following first order reaction

Where k is the rate constant.

and the initial concentrations of A and B are

What is the percent conversion after 500 seconds? Round to the nearest percent.

Possible Answers:

Correct answer:

Explanation:

For a first order reaction,

Integrating both sides gives

Where  is an integration constant.

Solving for  gives

Initially  there are 3 mols of . Using this we find that

At ,

Percent conversion is calculated as follows:

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