Introduction to Chemical Reactions Answers

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1
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Which indicator of a chemical reaction is shown in the picture?

A
the formation of a gas
B
the formation of a precipitate
C
a change in energy
2
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✔ exothermicendothermicneither

A
✔ exothermic
B
endothermic
C
neither
3

✔ exothermicendothermicneither

A
✔ exothermic
B
endothermic
C
neither
4

exothermicendothermic✔ neither

A
exothermic
B
endothermic
C
✔ neither
5

When potassium iodide liquid is poured into lead nitrate solution (both clear solutions), a bright yellow solid, lead iodide, forms in a potassium nitrate solution. What are the signs that this is a chemical reaction? Check all that apply.

A
Heat is produced.
B
Light is produced.
C
Heat is absorbed.
D
Bubbles appear.
E
A precipitate forms.
F
The color changes.
6

exothermicendothermicneither

A
exothermic
B
endothermic
C
neither
7

A food item that is left out of the refrigerator turns brown and forms bubbles and gas. What are the signs that this is a chemical reaction? Check all that apply.Heat is produced.Heat is absorbed.Bubbles appear.A precipitate forms.The color changes.

A
Heat is produced.
B
Heat is absorbed.
C
Bubbles appear.
D
A precipitate forms.
E
The color changes.
8

Pure sodium metal placed in water will spark and ignite, as well as form bubbles and gas. What are the signs that this is a chemical reaction? Check all that apply.Heat is produced.Light is produced.Heat is absorbed.Bubbles appear. A precipitate forms.The color changes.

A
Heat is produced.
B
Light is produced.
C
Heat is absorbed.
D
Bubbles appear.
E
A precipitate forms.
F
The color changes.
9

Write a description of how you know a chemical reaction is occurring.

Answer:

A chemical reaction can be identified by the formation of new substances with different properties. Common signs that a reaction is occurring include a change in color, the production of a gas (bubbles), the formation of a solid precipitate, or a change in energy such as the release or absorption of heat or light.

10

Which indicator of a chemical reaction is shown in the picture?

A
the formation of a gas
B
the formation of a precipitate
C
a change in energy
11

Karina strikes a match to light a candle. Explain what type of reaction the burning match represents in terms of energy.

Answer:

A burning match represents an exothermic reaction because energy is released in the form of heat and light during the chemical process.

12

When potassium iodide liquid is poured into lead nitrate solution (both clear solutions), a bright yellow solid, lead iodide, forms in a potassium nitrate solution. What are the signs that this is a chemical reaction? Check all that apply.

A
Heat is produced.
B
Light is produced.
C
Heat is absorbed.
D
Bubbles appear.
E
A precipitate forms.
F
The color changes.
13

Identify the chemical reactions as endothermic, exothermic, or neither.

Answers:
An egg cooking::endothermic
A candle burning::exothermic
Plaster and water combining and becoming warm::exothermic
Salt being added to water, with no change in temperature::neither
14

An egg cooking: [___]

A
exothermic
B
endothermic
C
neither
15

Theo mixes cake batter and places it in the oven at 350°F for 45 minutes. Explain what type of reaction baking a cake represents in terms of energy.

Answer:

Baking a cake represents an endothermic reaction. This is because heat energy from the oven must be absorbed by the batter for the chemical reactions (cooking) to occur. In an endothermic reaction, energy is taken in from the surroundings.

16

Pure sodium metal placed in water will spark and ignite, as well as form bubbles and gas. What are the signs that this is a chemical reaction? Check all that apply.Heat is produced.Light is produced.Heat is absorbed.Bubbles appear. A precipitate forms.The color changes.

A
Heat is produced.
B
Light is produced.
C
Heat is absorbed.
D
Bubbles appear.
E
A precipitate forms.
F
The color changes.
17

Which did you include in your response? Check all that apply.

A
Chemical reactions involve two or more chemical substances.
B
Chemical reactions result in new substance formation and are irreversible.
C
Signs of chemical reactions include gas formation, heat release or absorption, precipitate formation, and color change.
18

What facts did you include in your response? Check all that apply.

A
Burning a match represents an exothermic reaction.
B
Chemicals release energy in the form of heat and light.
19

A candle burning: [___]

A
exothermic
B
endothermic
C
neither
20

What facts did you include in your response? Check all that apply.

A
Baking a cake requires heat to be added.
B
The heat absorbed by the ingredients indicates that an endothermic reaction has occurred.

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