section: what is chemistry?
complete each statement below by underlining the correct word or phrase in brackets.
1. a chemical is any substance that has definite, indefinite composition.
changes in chemicals, or chemical reactions, take place only in test tubes, all around us.
2. the type and arrangement of particles, crystals in a sample of matter determine the properties of the matter. most of the matter you encounter is in one of numerous, three states of matter.
3. the characteristics of a solid include fixed, variable volume and shape.
particles that make up solids are held loosely, tightly in a flexible, rigid structure, so the particles can vibrate only slightly, flow past each other.
4. liquids have a fixed, variable volume but a fixed, variable shape. this situation occurs because particles in a liquid are held tightly, loosely and can, cannot slip past each other.
5. gases have fixed, variable volume and fixed, variable shape. gas particles may move apart to fill any container they occupy. this behavior occurs because gas particles are close together, far apart and are attracted, not stongly attracted to one another.
6. physical, chemical changes are changes in which the identity of a substance does not change. thus the changes of state are physical, chemical changes.
7. in a physical, chemical change, the identities of substances change and new substances form.
8. in the word equation hydrogen + oxygen + heat → water, hydrogen is a reactant, product, and water is a reactant, product. this is an example of a physical, chemical change.
9. a physical, chemical reaction rearranges the atoms that make up the reactant or reactants. after a chemical reaction, the same, different atoms are present in the product or products. atoms are, are not destroyed or created, so mass does, does not change during a chemical reaction.
10. chemical changes sometimes produce a gas, which you can detect by observing bubbles, a precipitate or by a change in color, odor.
11. when two clear solutions mix and a precipitate forms, the mixture becomes clear, cloudy.
12. when energy is released during a chemical reaction, temperature increases, decreases. chemical reactions may also absorb energy, which is indicated by a(n) increase, decrease in temperature.
13. a color change in a reaction system, such as when an indicator changes color, may indicate that a chemical, physical reaction has occurred and new, no new substances have formed.

Question

section: what is chemistry?
complete each statement below by underlining the correct word or phrase in brackets.
1. a chemical is any substance that has definite, indefinite composition.
   changes in chemicals, or chemical reactions, take place only in test tubes, all around us.
2. the type and arrangement of particles, crystals in a sample of matter determine the properties of the matter. most of the matter you encounter is in one of numerous, three states of matter.
3. the characteristics of a solid include fixed, variable volume and shape.
   particles that make up solids are held loosely, tightly in a flexible, rigid structure, so the particles can vibrate only slightly, flow past each other.
4. liquids have a fixed, variable volume but a fixed, variable shape. this situation occurs because particles in a liquid are held tightly, loosely and can, cannot slip past each other.
5. gases have fixed, variable volume and fixed, variable shape. gas particles may move apart to fill any container they occupy. this behavior occurs because gas particles are close together, far apart and are attracted, not stongly attracted to one another.
6. physical, chemical changes are changes in which the identity of a substance does not change. thus the changes of state are physical, chemical changes.
7. in a physical, chemical change, the identities of substances change and new substances form.
8. in the word equation hydrogen + oxygen + heat → water, hydrogen is a reactant, product, and water is a reactant, product. this is an example of a physical, chemical change.
9. a physical, chemical reaction rearranges the atoms that make up the reactant or reactants. after a chemical reaction, the same, different atoms are present in the product or products. atoms are, are not destroyed or created, so mass does, does not change during a chemical reaction.
10. chemical changes sometimes produce a gas, which you can detect by observing bubbles, a precipitate or by a change in color, odor.
11. when two clear solutions mix and a precipitate forms, the mixture becomes clear, cloudy.
12. when energy is released during a chemical reaction, temperature increases, decreases. chemical reactions may also absorb energy, which is indicated by a(n) increase, decrease in temperature.
13. a color change in a reaction system, such as when an indicator changes color, may indicate that a chemical, physical reaction has occurred and new, no new substances have formed.

Accepted Answer

### Question 1
# Brief Explanations:
A chemical has a definite composition (by definition of a chemical substance). Chemical reactions occur all around us (not just in test tubes).
# Answer:
1. A chemical is any substance that has $\underline{	ext{definite}}$ composition.
Changes in chemicals, or chemical reactions, take place $\underline{	ext{all around us}}$.

### Question 2
# Brief Explanations:
The properties of matter are determined by the type and arrangement of particles (not crystals, as crystals are a form of matter). Matter exists in three main states (solid, liquid, gas).
# Answer:
2. The type and arrangement of $\underline{	ext{particles}}$ in a sample of matter determine the properties of the matter. Most of the matter you encounter is in one of $\underline{	ext{three}}$ states of matter.

### Question 3
# Brief Explanations:
Solids have fixed volume and shape. Their particles are held tightly in a rigid structure, allowing only slight vibration (not flow, which is for liquids/gases).
# Answer:
3. The characteristics of a solid include $\underline{	ext{fixed}}$ volume and shape.
Particles that make up solids are held $\underline{	ext{tightly}}$ in a $\underline{	ext{rigid}}$ structure, so the particles can $\underline{	ext{vibrate only slightly}}$.

### Question 4
# Brief Explanations:
Liquids have fixed volume (they don’t compress much) but variable shape (they take the shape of their container). Particles are held loosely enough to slip past each other (enabling flow).
# Answer:
4. Liquids have a $\underline{	ext{fixed}}$ volume but a $\underline{	ext{variable}}$ shape. This situation occurs because particles in a liquid are held $\underline{	ext{loosely}}$ and $\underline{	ext{can}}$ slip past each other.

### Question 5
# Brief Explanations:
Gases have variable volume and shape (they expand to fill their container). Particles are far apart and not strongly attracted (allowing free movement).
# Answer:
5. Gases have $\underline{	ext{variable}}$ volume and $\underline{	ext{variable}}$ shape. Gas particles may move apart to fill any container they occupy. This behavior occurs because gas particles are $\underline{	ext{far apart}}$ and are $\underline{	ext{not strongly attracted}}$ to one another.

### Question 6
# Brief Explanations:
Physical changes do not alter the substance’s identity (e.g., melting ice). Changes of state (like melting, freezing) are physical changes.
# Answer:
6. $\underline{	ext{Physical}}$ changes are changes in which the identity of a substance does not change. Thus the changes of state are $\underline{	ext{physical}}$ changes.

### Question 7
# Brief Explanations:
Chemical changes involve a change in substance identity (new substances form, e.g., burning wood).
# Answer:
7. In a $\underline{	ext{chemical}}$ change, the identities of substances change and new substances form.

### Question 8
# Brief Explanations:
In a reaction, reactants are the starting materials (hydrogen, oxygen), products are the end materials (water). Forming water from hydrogen and oxygen is a chemical change (new substance).
# Answer:
8. In the word equation $\boldsymbol{	ext{hydrogen + oxygen + heat}
ightarrow 	ext{water}}$, hydrogen is a $\underline{	ext{reactant}}$, and water is a $\underline{	ext{product}}$. This is an example of a $\underline{	ext{chemical}}$ change.

### Question 9
# Brief Explanations:
Chemical reactions rearrange atoms (physical changes do not). Atoms are conserved (same atoms, not destroyed/created), so mass is conserved (does not change).
# Answer:
9. A $\underline{	ext{chemical}}$ reaction rearranges the atoms that make up the reactant or reactants. After a chemical reaction, $\underline{	ext{the same}}$ atoms are present in the product or products. Atoms $\underline{	ext{are not}}$ destroyed or created, so mass $\underline{	ext{does not}}$ change during a chemical reaction.

### Question 10
# Brief Explanations:
Gas production in a chemical change is seen as bubbles (precipitate is a solid). Odor change is not specific to gas production; bubbles are a direct sign of gas.
# Answer:
10. Chemical changes sometimes produce a gas, which you can detect by observing $\underline{	ext{bubbles}}$ or by a change in $\underline{	ext{odor}}$ (Note: For gas detection, bubbles are more direct, but the question includes "or"—the first blank is bubbles, second is odor as a possible indicator).

### Question 11
# Brief Explanations:
A precipitate is a solid, so mixing clear solutions to form a precipitate makes the mixture cloudy (not clear).
# Answer:
11. When two clear solutions mix and a precipitate forms, the mixture becomes $\underline{	ext{cloudy}}$.

### Question 12
# Brief Explanations:
Releasing energy (exothermic) increases temperature. Absorbing energy (endothermic) decreases temperature.
# Answer:
12. When energy is released during a chemical reaction, temperature $\underline{	ext{increases}}$. Chemical reactions may also absorb energy, which is indicated by a(n) $\underline{	ext{decrease}}$ in temperature.

### Question 13
# Brief Explanations:
A color change (e.g., indicator) signals a chemical reaction (new substance forms, as chemical changes create new materials).
# Answer:
13. A color change in a reaction system, such as when an indicator changes color, may indicate that a $\underline{	ext{chemical}}$ reaction has occurred and $\underline{	ext{new}}$ substances have formed.

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