Q: Which of the following is the correct formula for calculating the average atomic mass of an element with two isotopes?

$$\text{Average atomic mass} = (\text{mass}_1 \times \text{fraction}_1) + (\text{mass}_2 \times \text{fraction}_2)$$

Q: Which of the following is the correct relationship for converting between moles and number of particles?

$$\text{Number of particles} = \text{Number of moles} \times 6.022 \times 10$$^{23}$$

Question 1

Which of the following best describes the Law of Conservation of Energy as it applies to a chemical reaction in a closed system?

Accepted Answer

The total energy of the system and surroundings remains constant; energy can only change forms.

Question 2

A block of ice melts in your hand. Which of the following statements correctly describes the energy transfer?

Accepted Answer

The process is endothermic; heat is absorbed by the ice from your hand.

Question 3

Which equation correctly represents the calculation of kinetic energy for a moving object?

Accepted Answer

$$KE = \frac{1}{2}mv^2$

Question 4

Which of the following phase changes is classified as exothermic?

Accepted Answer

Condensation

Question 5

A sample of water vapor condenses into liquid water. What happens to the thermal energy of the system?

Accepted Answer

The system releases heat to the surroundings.

Question 6

Which of the following best describes a compound?

Accepted Answer

A pure substance composed of two or more elements in fixed, definite proportions.

Question 7

Which of the following is a physical property of matter?

Accepted Answer

Melting point

Question 8

Which of the following statements about the periodic table is correct?

Accepted Answer

Elements in the same group have similar chemical properties.

Question 9

A neutral atom of sodium (Na) has 11 protons. How many electrons does it have?

Accepted Answer

11

Question 10

Which of the following is the correct formula for calculating the average atomic mass of an element with two isotopes?

Accepted Answer

$$	ext{Average atomic mass} = (	ext{mass}_1 	imes 	ext{fraction}_1) + (	ext{mass}_2 	imes 	ext{fraction}_2)$$

Question 11

A sample contains $$4.60 	imes 10$$^{21}$$ atoms of platinum (Pt). If the atomic mass of Pt is 195.1 amu/atom and 1$$ 	ext{ amu} = 1.661 	imes $$10^{-24}$$ 	ext{ g}$$, what is the mass of Pt in the sample?

Accepted Answer

$$1.5 	ext{ g}$$

Question 12

Which of the following best describes a heterogeneous mixture?

Accepted Answer

A mixture with visibly distinct parts and non-uniform composition

Question 13

Which of the following elements is a main group element?

Accepted Answer

Calcium (Ca)

Question 14

Which of the following is a correct statement about ions?

Accepted Answer

Cations have fewer electrons than protons.

Question 15

A sample of CO$$_2$$ and SO$$_2$$ each have the same mass. Which sample contains more molecules?

Accepted Answer

CO$$_2$$

Question 16

Which of the following is a chemical property?

Accepted Answer

Ability to react with water

Question 17

Which of the following best describes the difference between a molecule and a compound?

Accepted Answer

A molecule consists of two or more atoms chemically bonded; a compound consists of two or more different elements chemically bonded.

Question 18

Which of the following phase changes is endothermic?

Accepted Answer

Sublimation

Question 19

Which of the following is the correct relationship for converting between moles and number of particles?

Accepted Answer

$$	ext{Number of particles} = 	ext{Number of moles} 	imes 6.022 	imes 10$$^{23}$$

Introduction to Chemistry: Matter, Energy, Atomic Structure, and the Periodic Table

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