Introduction to Chemical Reactions Answers

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Which is evidence that a chemical reaction has likely occurred?

A
a liquid slowly losing volume
B
the formation of a precipitate
C
boiling water releasing steam
D
a change in the shape of a solid
3

Which best explains why a firework being ignited is an example of an exothermic reaction and not an endothermic reaction?

A
The fireworks produce colors.
B
The fireworks give off heat.
C
Igniting the fireworks requires energy.
D
Igniting the fireworks makes an odor.
4

Which of these most likely represents a chemical change?

A
water boiling
B
sugars digested by saliva
C
mud drying to dirt
D
ice cream melting
5

Two chemicals react in an endothermic reaction. What can be known about this reaction?

A
Heat is absorbed because the old substance needs more energy to break its bonds.
B
Heat is released because the old substance needs less energy to break its bonds.
C
A precipitate will form as a result of the reaction.
D
A gas will form as a result of the reaction.
6

Which best describes what happens to the atoms in a chemical reaction?

A
they are rearranged
B
many of them disappear
C
all of them form stronger bonds
D
all of them remain unchanged
7

Theresa creates an experiment where she mixes two red-colored substances together in a container and observes the solution slowly changing from red to blue for the next eight minutes. The solution becomes completely blue after eight minutes.

A
A chemical change started immediately and finished at eight minutes.
B
A non-chemical change started immediately and finished at eight minutes.
C
A chemical change occurred at four minutes.
D
A non-chemical change occurred at four minutes.
8

What must occur in order for a chemical reaction to be specifically classified as endothermic instead of exothermic?

A
Atoms are rearranged.
B
Chemical bonds are formed.
C
Energy is released in the form of heat.
D
Energy is absorbed in the form of heat.
9

Which is an example of a chemical reaction?

A
paper folded into tiny pieces
B
paper burned and turned into smoke
C
paper soaked in water
D
paper shredded and turned into pulp
10

When baking soda and vinegar react, the surface bubbles. What does this most likely indicate?

A
a chemical change, because a precipitate is being formed
B
a chemical change, because a gas is being formed
C
a non-chemical change, because a precipitate is being formed
D
a non-chemical change, because a gas is being formed

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