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Scenes A-D represent atomic-scale views of different samples of substances:
- Under one set of conditions, the substances in A and B mix, and the result is depicted in C. Does this represent a chemical or a physical change?
- Under a second set of conditions, the same substances mix, and the result is depicted in D. Does this represent a chemical or a physical change?
- Under a third set of conditions, the same substances mix, and the result is depicted in D. Does this represent a chemical or a physical change?
- After the change in part(c) has occurred, does the sample have different chemical properties? Physical properties?
a)
Interpretation: Whether combination of A and B to form C is physical or chemical change should be determined.
Concept introduction: Changes can be classified as physical and chemical changes. Physical changes are such changes that allow change of state of matter only but not formation of new substances. Reversal of such changes is possible by physical methods.
Chemical changes allow formation of new and different substances from original substances via chemical reactions. These cannot be reversed back to original state by any method.
Explanation of Solution
Substances that are present in A and B have completely different properties than those formed in C. So when A and B are mixed to form C, it refers to chemical change.
b)
Interpretation: Whether combination of A and B to form D is physical or chemical change should be determined.
Concept introduction:Changes can be classified as physical and chemical changes. Physical changes are such changes that allow change of state of matter only but not formation of new substances. Reversal of such changes is possible by physical methods.
Chemical changes allow formation of new and different substances from original substances via chemical reactions. These cannot be reversed back to original state by any method.
Explanation of Solution
Substances that are present in A and B have completely different properties than those formed in D. So when A and B are mixed to form D, a completely different substance is formed. Therefore combination of A and B to form D is chemical change.
c)
Interpretation: Whether conversion of C to D is physical or chemical change should be determined.
Concept introduction: Changes can be classified as physical and chemical changes. Physical changes are such changes that allow change of state of matter only but not formation of new substances. Reversal of such changes is possible by physical methods.
Chemical changes allow formation of new and different substances from original substances via chemical reactions. These cannot be reversed back to original state by any method.
Explanation of Solution
When sample in C is converted to D, there occurs difference in arrangement of particles only while substances remain same. Therefore it is physical change.
d)
Interpretation: Whether conversion of C to D is physical or chemical change should be determined.
Concept introduction: Changes can be classified as physical and chemical changes. Physical changes are such changes that allow change of state of matter only but not formation of new substances. Reversal of such changes is possible by physical methods.
Chemical changes allow formation of new and different substances from original substances via chemical reactions. These cannot be reversed back to original state by any method.
Explanation of Solution
When sample in C is converted to D, only arrangement of particles is changed while substances remain same. Therefore it is physical change and physical properties are changed in conversion of C to D.
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Chapter 1 Solutions
Principles of General Chemistry
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