Chemical Reactions and Review

Which of the following is an example of a chemical reaction?

• A marshmallow turning black when heated over a fire
• A powder dissolving in water to make lemonade
• An ice cube melting into a puddle of water
• Salt crystals being crushed into a powder
  

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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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You know you a chemical reaction has occurred if 

• there is a precipitate.
• there is a color change.
• there is a temperature change.
• All of these answers are evidence.

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Which of the following is evidence of a chemical reaction?

• fizzing
• water changing to ice
• saltwater
• paper being cut in half

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Which of the following is an example of a chemical change?

• rusting of a bicycle
• painting a house
• washing a dog
• tearing up a newspaper

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Which is an example of a physical change?

• sodium and chlorine form salt
• a copper ring turns white and green
• a log burns in a fire
• using sand and water to build a sand castle on a beach

Is burning wood a chemical or physical change?

• chemical
• physical

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Four students performed four different investigations by combining different substances. Their results are shown in the table provided. In which experiment are new substances being formed?

• Experiment 1
• Experiment 2
• Experiment 3
• Experiment 4

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A clear liquid from a flask is poured into another clear liquid in a beaker. Which of the following results of this procedure would indicate a new substance was formed?

• The level of the substance in the beaker is higher after the other liquid is added.
• A yellow solid forms and then settles to the bottom of the beaker.
• Small white crystals are left behind in the flask that held the first liquid.

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Which of the following is an example that includes evidence of a chemical reaction?

• A sample of zinc is placed in water and it settles to the bottom
• A solid block of ice is heated and it completely melts into a liquid. 
• Sugar that is burned gives off an odor and turns brown and then black.
• A tomato is placed into a blender and chopped up into smaller pieces.

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