AP Chemistry: 3.5 Kinetic Molecular Theory - Exam Style questions with Answer- MCQ

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Question

The diagrams above use arrows to represent the speed of a gas particle. Which of the diagrams best represents the speed of the particles of a gas at a fixed temperature, and why?

A Diagram 1, because all the particles have the same speed.

B Diagram 1, because the particles are moving in different directions.

C Diagram 2, because the particles have a net kinetic energy of zero.

D Diagram 2, because the particles have a variety of different speeds.

▶️Answer/Explanation

Ans: D

Based on kinetic molecular theory, gas particles have a distribution of speeds that is dependent on the temperature, which is represented in diagram 2.

Question

The two gas samples represented in the graph above are at the same temperature. Which of the following statements about the gases is correct?

A The molecules of gas $Z$ have a higher average kinetic energy than the molecules of gas $X$ .

B There are fewer molecules in the sample of gas $Z$ than in the sample of gas $X$ .

C Gas $Z$ has a smaller molar mass than gas $X$ .

D Gas

Z

has a greater molar mass than gas

X

▶️Answer/Explanation

Ans:C

Gases at the same temperature have the same average kinetic energy of their molecules. Since KE $=\frac{1}{2}m_Xv_Y^2=\frac{1}{2}m_Zv_Z^2$ $K E = \frac{1}{2} m_{X} v_{X}^{2} = \frac{1}{2} m_{Z} v_{Z}^{2}$ , the gas with the higher average molecular speed has the lower molar mass $m_X/v_Z=v_Z^2/v_X^2$ . The curve for gas $Z$ shows that the molecules have a higher average speed than the molecules in gas $X$ , so gas $Z$ has a smaller molar mass.

Question

The diagram above shows the distribution of speeds for a sample of $O 2, gaseous$ . Which of the following graphs shows the distribution of speeds for the same sample at a higher temperature (dashed line) ?

▶️Answer/Explanation

Ans: C

When the temperature increases, the average speed of the gas molecules increases. The peak is to the right of the original peak, and the relative number of molecules at the highest speeds is greater.

Question

The volume of a sample of air in a cylinder with a movable piston is 2.0 L at a pressure $P_1$ , as shown in the diagram above. The volume is increased to 5.0 L as the temperature is held constant. The pressure of the air in the cylinder is now $P_2$. What effect do the volume and pressure changes have on the average kinetic energy of the molecules in the sample?

(A)The average kinetic energy increases.

(B)The average kinetic energy decreases.

(C)The average kinetic energy stays the same.

(D) It cannot be determined how the kinetic energy is affected without knowing

▶️Answer/Explanation

Ans:C

Refer to the foll0wing.

The table below contains information about particles is samples of four different gases at 273 K. The (A) greatest in container I samples are in four identical rigid containers (B) greatest in container 2 numbered 1 through 4.

Question

Under the conditions given, consider containers 1, 2, and 4 only. The average speed of the gas particles is

(A) greatest in container 1

(B) greatest in container 2

(D) the same in containers 1, 2, and 4

▶️Answer/Explanation

Ans:A

AP Chemistry: 3.5 Kinetic Molecular Theory – Exam Style questions with Answer- MCQ

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