Chemical Reactions

Which of these observations is an indication that a chemical reaction has occurred?

• Steam forms above boiling water

• A solid forms when a clear solution is frozen

• A solid forms when two clear solutions are mixed

• Sugar crystals form on the sides of a boiling pot of sugar water

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112.20.b.5.E

Students performed a lab investigation on chemical reactions. The students put on goggles and plastic gloves and then followed these steps.

Which observation would indicate that a chemical reaction occurred?

• The vinegar took the shape of the container in step 1

• The steel wool sank in the vinegar in step 3

• The temperature of the vinegar increased during step 4

• The steel wool changed shape during step 6

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112.20.b.5.E

Students mixed two liquids in a beaker and listed their observations.

Based on these observations, which statement contains the best evidence that a chemical reaction occurred?

• There is a change in shape

• There is a change in volume

• The two liquids mix into a solution

• The two liquids form a new substance

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112.20.b.5.E

Which statement best describes evidence that a chemical reaction occurs as a cake bakes?

• The water in the cake batter evaporates

• The cake rises as gas bubbles form in the baking cake

• The cake takes the shape of the container in which it is baked

• The water is the cake batter is used to keep the cake moist as it bakes

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112.20.b.5.E

For a laboratory investigation some students put a strip of shiny metal into a beaker of blue solution and then stored the beaker on a shelf overnight. The next morning, the students recorded observations about the metal and the solution in the box below.

Based on their observations, can the students correctly conclude that a chemical reaction occurred?

• No, because the metal strip was still visible

• Yes, because a new material of a different color formed on part of the metal strip

• No, because the solution stayed blue

• Yes, because the volume of the blue solution stayed the same

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112.20.b.5.E

Which observation provides evidence of a chemical reaction?

• Hot water heated the aluminum foil

• The liquid solution changed color

• The pan was lined with aluminum foil

• The hot water cooled.

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112.20.b.5.E

Which statement is NOT supported by the student's observation?

• A chemical reaction takes place between magnesium and hydrochloric acid

• A gas is released in Test Tube 2

• The substances in both test tubes are reactive only at high temperatures

• Energy is released in the reaction involving hydrochloric acid

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112.20.b.5.E

Nitrogen dioxide is a gas that can be generated by emissions from vehicles and factories. It can also be generated by natural sources, such as forest fires, lightning, and microbial activity in soil. The equation is shown.

Which of these provides evidence that a chemical reaction occurs?

• A gas is present

• The total number of atoms remains unchanged

• The state of matter remains the same

• A brown gas is produced

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112.20.b.5.E

Coal contains carbon and other elements. Carbon dioxide forms when coal burns in the presence of oxygen. Which of these is the best evidence that a chemical reaction occurs when coal burns?

• The shape of the coal changes

• Oxygen is present

• A new substance is produced

• Coal is made up of more than one element

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112.20.b.5.E

For an investigation a student poured a blue solution of CuSO₄ into a beaker. The student placed a shiny, silver-colored strip of zinc metal in the solution and observed the changes. The student inferred that a chemical reaction occurred.

What evidence supports this inference?

• A dark solid formed on the zinc metal

• The zinc metal remained silver-colored and shiny

• The CuSO₄ solution turned blue when the zinc metal was added

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112.20.b.5.E