lesson review 3 · 2019. 10. 2. · lesson review answers 1. a change that affects the physical...
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LessonLesson ReviewVocabularyIn your own words, define the following terms.1 physical change
2 chemical change
3 law of conservation of mass
Key Concepts4 Identify Give an example of a physical change
and an example of a chemical change.
5 Compare How is a chemical change different from a physical change?
6 Apply Suppose a log’s mass is 5 kg. After burning, the mass of the ash is 1 kg. Explain what may have happened to the other 4 kg.
Critical ThinkingUse this photo to answer the following questions.
7 Analyze As the bright sun shines upon the water, the water slowly disappears. The sunlight also gives energy to the surrounding plants to convert water and carbon dioxide into sugar and oxygen gas. Which change is physical, and which is chemical?
8 Infer How does the law of conservation of energy relate to the processes going on in the water and in the plants?
9 Compare Relate the statement “You can’t get something for nothing” to the law of conservation of mass.
Lesson Review Answers 1. a change that affects the physical prop-
erties of a substance
2. a change that alters the chemical makeup of a substance
3. a law that states that mass cannot be created or destroyed in ordinary physical and chemical changes
4. Sample answer: Melting chocolate is a physical change. Baking a cake is a chemical change.
5. Chemical changes result in the formation of new substances with new chemical properties. Physical changes do not.
6. The other 4 kg could have been given off as gaseous substances.
7. Sample answer: Water is evaporating from the puddle, and that is a physical change. The plants are converting sub-stances into other substances (photo-synthesis), and that is a chemical change.
8. Sample answer: The law of conservation says that energy is not created or destroyed. So energy from the sun is absorbed by the water and converted into heat. Energy from the sun is absorbed by the plants and used to con-duct photosynthesis. That energy is the stored in the bonds of sugars made by the plants.
9. The law of conservation of mass states that you cannot create new matter from nothing. Therefore, you must start with something.
149Lesson 3 Physical and Chemical Changes
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4242 Unit 3 Matter
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