Instructions: Read the following and then complete the Reading & Evidence Table, using evidence from the text & your own research. Make sure answers use your own words.
Chemical vs. Physical Changes
Chemical and physical changes are fundamental concepts in the study of matter and its transformations. A physical change involves alterations in the physical state or appearance of a substance without changing its chemical composition. One example is the phase transition of water from a solid (ice) to a liquid (water) or a gas (steam). Physical changes do not affect the substance's reactivity or combustibility but can influence properties like density. For instance, as water transitions from ice to liquid, its density decreases, showcasing how physical changes impact specific characteristics of a substance.
Conversely, chemical changes involve the transformation of substances into new chemical entities with distinct properties. Reactivity and combustibility are often evident in chemical transformations. For instance, when iron reacts with oxygen in the presence of moisture, it forms rust—a chemical change characterized by the alteration in the composition of iron. Reactivity, in this context, refers to the propensity of a substance to undergo chemical reactions, while combustibility relates to its ability to burn.
The evidence of separating mixtures, development of a gas, formation of a precipitate, change in energy, color, and form can serve as key indicators to distinguish between physical and chemical changes in a substance. When dealing with mixtures, the ability to physically separate components without altering their chemical compositions typically points towards a physical change. On the other hand, the development of a gas or the formation of a precipitate often signifies a chemical change, as these reactions involve the creation of new substances with distinct properties. Changes in energy, either absorption or release, can also be indicative of a chemical transformation, as chemical reactions often involve the exchange or generation of energy. . Alterations in color can be a visual cue, with a change often associated with chemical reactions. Similarly, changes in form, such as the solidification of a liquid or the dissolution of a solid, are characteristic of physical changes. By carefully observing and interpreting these pieces of evidence, scientists and researchers can effectively identify and differentiate between physical and chemical changes in matter.
VII. Reading & Evidence Questions:
15. Using the text from above, what is the main difference between a physical and chemical change?
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16. With evidence from the text above, what are 3 different reactions that would demonstrate that a substance has undergone a chemical change?
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17. Why is melting ice a physical change and not a chemical change? Use the text for support.
Type Answer HERE:
Reading & Evidence Table:
| Reading & Evidence Questions | Responses based on Text & Research |
|----------------------------------|--------------------------------------|
| 15. Main difference between a physical and chemical change | The main difference is that physical changes involve alterations in the physical state or appearance of a substance without changing its chemical composition, while chemical changes involve the transformation of substances into new chemical entities with distinct properties. |
| 16. 3 reactions demonstrating a chemical change | Three reactions that would demonstrate a substance has undergone a chemical change are the development of a gas (e.g., baking soda and vinegar reaction), formation of a precipitate (e.g., mixing silver nitrate and sodium chloride to form silver chloride), and changes in energy (e.g., combustion reactions releasing energy). |
| 17. Why is melting ice a physical change | Melting ice is a physical change because it only involves the phase transition from a solid state to a liquid state without altering the chemical composition of the substance. The water molecules in ice remain the same during the melting process, making it a physical change. |