Chapter 2 Mass Changes in Closed Systems

The Law of Conservation of Mass States

• Energy cannot be created nor destroyed, it can only change form.

• Mass cannot be created nor destroyed, it can only change form.

• Matter cannot be created nor destroyed, it can only change form.

• Mass can be created or destroyed, it cannot change form.

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What is a closed system?

• a system where none of the reactants or products are allowed to escape
• compounds made of thousands of repeating smaller molecules
• the output, or result of a chemical reaction
• occurs when the atoms and molecules of two or more substances rearrange to form new substances

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Fill in the blank:
It is best to observe the law of conservation of mass in a _____________________ because it will ensure that the mass is the same in the beginning and end of a chemical reaction.

• closed
• open
• balanced
• rearranged

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In a closed system, a chemical reaction takes place.  The mass of the reactants in the beginning of the reaction is 25g.  What does the mass have to be in the end of the reaction in order to follow the law of conservation of mass?

• 25g
• You can't tell with the given information.
• 30g
• 15g

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In a closed system, a chemical reaction takes place.  The mass of the reactants in the beginning of the reaction is 25g.  What does the mass have to be in the end of the reaction in order to follow the law of conservation of mass?

• 25g
• You can't tell with the given information.
• 30g
• 15g

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NGSS.MS-PS1-5

Measure of the amount of matter 

• mass
• volume
• weight
• density

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Suppose a reaction were to happen in an open container in a lab.  During the reaction, the scientist observes the chemicals bubble, and produce a gas.   During the analysis the scientist notices that the reactants weighed 20 g when he started, and the product weighed 18 g.  Explain what happened.  

• His chemical reaction defied the law of conservation of mass
• The product destroyed mass during the reaction
• The reactants created matter during the reaction
• The gas that was produced was not able to be weighed since the container was open.  

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Evidence of a chemical reaction include:

• Phase change
• No new substance
• Bubbles forming
• Shape change

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How is a physical change different from a chemical change?

• There is absolutely no difference
• Chemical changes produce a new substance, physical changes stay the same substance
• Chemical changes create and destroy matter, physical changes don't
• Physical changes create and destroy matter, chemical changes dont

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Students react baking soda & vinegar.
Which of the following would provide the evidence that the number of atoms present before a chemical reaction is equal to the number of atoms present after the chemical reaction?

• The mass of the plastic bag, baking soda, and vinegar before the reaction was equal to the mass after the reaction.
• Bubbles were produced during the reaction, which meant that a gas was being produced.
• The plastic bag did not change in any way, indicating that it was not involved in the reaction.
• The mass of the baking soda was exactly equal to the mass of the vinegar used to create the chemical reaction.

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