8th Grade Science Review 13 (Chemical Reactions)

The picture above shows a light stick. Light sticks begin to glow when the vial inside the stick is broken. Chemicals inside the vial mix with chemicals outside of the vial. Which of the following statements BEST supports the idea that a chemical reaction, rather than a physical change, is occurring?

• The vial is broken into smaller pieces.
  
• Energy is released in the form of light.
  
• Two different substances are combined.
• The substances are in a flexible container.

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NGSS.MS-PS1-2

NGSS.MS-PS1-5

Which chemical equation best illustrates the law of conservation of mass?

• 2Al+CuO -> Al₂O₃ +3Cu
• 2Al+3CuO -> Al₂O₃ +Cu
• 2Al + 3CuO -> Al₂O₃ + 3Cu
• 3Al + 2CuO ->  Al₂O₃ + 2Cu

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NGSS.MS-PS1-5

Some spoons are made with the element silver (Ag). Over time, these spoons will turn black if they are not cleaned with a special solution. Which of the following statements BEST explains why the element silver in the spoons turns black?

• It absorbs energy when exposed to warm food.
  
• It breaks down into smaller and smaller particles.
  
• It reacts with substances in the air to form a new substance.
  
• It changes from one phase of matter into another phase of matter.

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NGSS.MS-PS1-2

Which of the following contains one oxygen atom?

• H₂O
• CO₂
• 2N₂O
• Co

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NGSS.MS-PS1-1

Which process causes substances to react to form one or more new substances?

• chemical change
• physical change
• evaporation
  
• freezing

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NGSS.MS-PS1-2

NGSS.MS-PS1-5

Which chemical equation correctly shows the formation of water from hydrogen and oxygen?

• H₂ +O₂ =H₂O
• 2H₂ +O₂ =2H₂O
• H₂ +2O=H₂O
• H+O₂ =H₂O

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NGSS.MS-PS1-1

NGSS.MS-PS1-5

A scientist carries out a reaction in a test tube. After the bubbling stops, she notices that the test tube is very warm. What might she conclude about the reaction?

• The reaction happened very quickly.
• The reaction is endothermic.
• The reaction is exothermic.
• No reaction took place.

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NGSS.MS-PS1-4

NGSS.MS-PS3-4

NGSS.MS-PS3-5

A substance that is used to speed up a chemical reaction is called

• a reactant.
• an inhibitor.
• a precipitate.
• a catalyst.

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NGSS.HS-PS1-5

During a laboratory experiment, Tran applied the law of conservation of energy. Which of the following did he assume to be true?

• Energy is not changed.
• Energy is not created or destroyed.
• The total energy of the reactants is greater than the total energy of the products.
• The total energy of the reactants is less than the total mass of the products.

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NGSS.MS-PS3-4

NGSS.MS-PS3-5