Introduction Chemical Reactions

Which is an example of a chemical reaction?

• paper folded into tiny pieces

• paper burned and turned into smoke

• paper soaked in water

• paper shredded and turned into pulp

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

• they are rearranged

• many of them disappear

• all of them form stronger bonds

• all of them remain unchanged

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Pedro wants to create a chemical reaction between oil and water. He adds oil to a beaker of water and notices that the liquids do not mix. He then shakes the beaker and the drops of oil become suspended through the water for a few moments before returning to their separate layers.

Did Pedro succeed in creating a chemical change?

• Yes, because the oil was evenly suspended.

• Yes, because the solution was permanently changed.

• No, because the oil only briefly mixed with the water.

• No, because no new substances were formed.

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Reggie and Charlotte are baking oatmeal cookies. They dip the baked cookies in melted chocolate. The chocolate cools to form a hardened coating. Reggie argues the entire chocolate-covered cookie has undergone a chemical change. Charlotte disagrees, saying only the original oatmeal cookie has undergone a chemical change, not the chocolate coating.

Who is correct?

• Reggie, because baking and melting cause bonds to be broken, leading to a chemical change.

• Reggie, because objects that are heated always undergo chemical changes.

• Charlotte, because melting objects only sometimes cause a chemical change.

• Charlotte, because baking causes a chemical change, but melting objects is a non-chemical change.

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Which of these most likely represents a chemical change?

• water boiling

• sugars digested by saliva

• mud drying to dirt

• ice cream melting

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Which is evidence that a chemical reaction has likely occurred?

• a liquid slowly losing volume

• the formation of a precipitate

• boiling water releasing steam

• a change in the shape of a solid

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When liquid silver nitrate and liquid sodium chloride are combined, solid silver chloride forms along with a new liquid, sodium nitrate. Which substance represents the precipitate?

• silver nitrate

• silver chloride

• sodium chloride

• sodium nitrate

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

• a chemical change, because a precipitate is being formed

• a chemical change, because gas is being formed

• a non-chemical change, because a precipitate is being formed

• a non-chemical change, because a gas is being formed

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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.

What does this represent about the type of change happening in the container?

• A chemical change started immediately and finished at eight minutes.

• A non-chemical change started immediately and finished at eight minutes.

• A chemical change occurred at four minutes.

• A non-chemical change occurred at four minutes.

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When vinegar and baking soda react, the mixture becomes cold to the touch and a gas and a new liquid substance are formed.

Which best describes what is occurring in the reaction?

• The reaction is chemical and endothermic.

• The reaction is chemical and exothermic.

• The reaction is non-chemical and endothermic.

• The reaction is non-chemical and exothermic.

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