Question 1

Which of the following best describes the contents of the box containing only Zn spheres in the first image?

Accepted Answer

An element, because it contains only zinc atoms.

Question 2

In the second image, each sphere represents an oxygen atom. If there are 8 spheres grouped in pairs, how many molecules and atoms are present?

Accepted Answer

4 molecules and 8 atoms.

Question 3

Which of the following best describes the difference in particle arrangement between a solid, liquid, and gas?

Accepted Answer

Particles in a solid are closely packed and fixed, in a liquid are close but can move past each other, and in a gas are far apart and move freely.

Question 4

Which of the following is a correct distinction between a homogeneous mixture and a heterogeneous mixture?

Accepted Answer

A homogeneous mixture has a uniform composition throughout, while a heterogeneous mixture has visibly different parts.

Question 5

Which of the following is a chemical property?

Accepted Answer

When paper burns, it forms new compounds, carbon dioxide and water.

Question 6

In the image showing the change from hydrogen and oxygen atoms to water molecules, what type of change is occurring?

Accepted Answer

A chemical change, because new substances (water) are formed from hydrogen and oxygen.

Question 7

After the reaction between hydrogen and oxygen to form water, how many molecules are present if you start with 4 molecules of $$\mathrm{O_2$}$$ and 8 molecules of $$\mathrm{H_2$}$$?

Accepted Answer

8 molecules of water, because $$2\mathrm{H_2$} + \mathrm{O_2$} \rightarrow 2\mathrm{H_2O}.$$

Question 8

Which of the following best explains why the reaction between hydrogen and oxygen to form water is exothermic?

Accepted Answer

The products (water) are more stable and have lower potential energy than the reactants, releasing energy.

Question 9

Which of the following is the best definition of a hypothesis?

Accepted Answer

A tentative explanation that can be tested by experiments.

Question 10

Which of the following statements about scientific theories and laws is correct?

Accepted Answer

A scientific theory explains why phenomena occur, while a law describes what happens.

Question 11

Which of the following best describes a paradigm in science?

Accepted Answer

A set of beliefs or assumptions that guide scientific research.

Question 12

If a sample contains only $$\mathrm{Ne}$$ atoms, as shown in one of the boxes, what type of substance is it?

Accepted Answer

An element.

Question 13

Which of the following is an example of a heterogeneous mixture?

Accepted Answer

Sand and iron filings.

Question 14

Which of the following is a physical change?

Accepted Answer

Dissolving sugar in water.

Question 15

A student observes that when two clear solutions are mixed, a yellow solid forms. What type of change has occurred?

Accepted Answer

A chemical change, because a new substance (precipitate) formed.

Question 16

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

Accepted Answer

An element contains only one type of atom, while a compound contains two or more types of atoms chemically combined.

Question 17

Which of the following is a correct example of a homogeneous mixture?

Accepted Answer

Salt water.

Question 18

If a reaction absorbs heat from the surroundings, what type of reaction is it?

Accepted Answer

Endothermic.

Question 19

Which of the following best describes the law of conservation of mass as it applies to chemical reactions?

Accepted Answer

The total mass of reactants equals the total mass of products.

Question 20

A student claims that a hypothesis is the same as a theory. Which of the following best corrects this misconception?

Accepted Answer

A hypothesis is a tentative explanation that can be tested, while a theory is a well-supported explanation based on evidence.

Introduction to Chemistry: Describing Matter and the Scientific Method

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