Chemical Reactions and Conservation of Mass

Which of the following is true of the law of conservation of mass?

• The same number and type of each atom will always be present before and after a chemical reaction takes place.
• Some of the atoms present before the reaction will always be lost during a chemical reaction.
• Some of the atoms will always be changed into a different type of atom by a chemical reaction.
• During a chemical reaction, atoms will always be combined into much larger molecules.

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Which of the following is the best description of the results of a chemical reaction?

• The substance seems to disappear after dissolving in water.
• The substance changes from liquid to solid at a low temperature.
• The reaction can be reversed to get back the original substance.
• A new substance with different properties is formed.

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Endothermic reactions...

• release energy
• explode
• take in energy
• have higher energy in their reactants than the products

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Exothermic reactions

• have higher energy in their products than their reactants
• release energy
• get cold
• are synthesis reactions

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Which of the following is not evidence of a chemical reaction?

• gas produced
• precipitate formation
• color change
• mass change

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The substances listed to the left of the arrow in a chemical reaction are called the _______________.

• products
• reactants
• substances
• materials

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How many Al atoms are in this compound?         4Al₂O₃

• 2
• 8
• 6
• 4

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How many F atoms are in this compound?
6MgF₂ 

• 2
• 6
• 8
• 12

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Can matter be created or destroyed?

• Yes, it can be created.
• Yes, it can be destroyed.
• No, matter is always conserved
• None of these

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Why does this picture demonstrate the Law of Conservation of Mass?

• the number of atoms of each element are the same on both sides

• they start out separate and end up combined

• the same elements are used

• it doesn't demonstrate the Law of Conservation of Mass

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