AnswersPhysical ScienceIntroduction to Chemical Reactions

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1
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Which statement best describes the difference between endothermic and exothermic reactions?

A
They are opposites because endothermic reactions release energy and exothermic reactions require energy.
B
They the same because they are both ways of forming gasses.
C
They the same because they are both ways of forming precipitates.
D
They are opposites because endothermic reactions require energy and exothermic reactions release energy.
2
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Which best describes what happens to the atoms in a chemical reaction?

A
they are rearranged
B
all of them remain unchanged
C
many of them disappear
D
all of them form stronger bonds
3

Which is an example of a chemical reaction?

A
paper folded into tiny pieces
B
paper soaked in water
C
paper shredded and turned into pulp
D
paper burned and turned into smoke
4

Which of these most likely represents a chemical change?

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

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

A
a non-chemical change, because a gas is being formed
B
a chemical change, because a gas is being formed
C
a chemical change, because a precipitate is being formed
D
a non-chemical change, because a precipitate is being formed
6

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
A precipitate will form as a result of the reaction.
C
Heat is released because the old substance needs less energy to break its bonds.
D
A gas will form as a result of the reaction.
9

Which best describes what is occurring in the reaction? When vinegar and baking soda react, the mixture becomes cold to the touch and a gas and a new liquid substance are formed.

A
The reaction is chemical and endothermic.
B
The reaction is non-chemical and endothermic.
C
The reaction is chemical and exothermic.
D
The reaction is non-chemical and exothermic.

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