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  1. Classify each change as physical or chemical.
ACrushing an aluminum can
BRecycling used aluminum cans to make new ones
CAluminum combining with oxygen to form aluminum oxide


  1. Describe the results of a physical change and list three examples of a physical change.


  1. Describe the results of a chemical change. List four indicators of a chemical change.


  1. Calculate/Solve each of the following:
AIf 22.99 g of sodium and 35.45 g of chlorine fully react, how much sodium chloride forms?
BA 12.2 g sample of X reacts with a sample of Y to form 78.9 g of XY. What mass of Y reacted?


  1. Evaluate: A friend tells you, "Because composition does not change during a physical change, the appearance of a substance does not change." Is your friend correct? Explain.

Verified Answer :

Final answer:

In this response, we classify changes as physical or chemical, explain the results of each type of change, and provide examples. We also address calculations regarding mass changes and evaluate a friend's statement about physical changes. The distinctions between physical and chemical processes are key aspects.


Explanation:

Classification of Changes

  1. Crushing an aluminum can: This is a physical change because it alters the shape and size of the can without changing its chemical composition.
  2. Recycling used aluminum cans to make new ones: This is also a physical change since the aluminum is processed and reshaped, but the chemical structure remains the same.
  3. Aluminum combining with oxygen to form aluminum oxide: This represents a chemical change because it involves a reaction between aluminum and oxygen, resulting in a new substance (aluminum oxide).

Physical vs. Chemical Change

Results of a physical change include alterations in appearance, such as shape, size, or state of matter, without a change in chemical composition. Examples include:

  • Melting ice to water
  • Cutting paper
  • Boiling water into steam

Describing Chemical Changes

Results of a chemical change include the formation of new substances with different properties. Indicators of a chemical change can include:

  • Change in color
  • Production of gas (bubbling or fizzing)
  • Formation of a precipitate (solid) from a solution
  • Change in temperature or energy release/absorption

Calculations

  1. For the reaction of sodium (22.99 g) and chlorine (35.45 g): According to the law of conservation of mass, if the reaction goes to completion, the total mass of sodium chloride formed will be the sum of the reactants: 22.99 g + 35.45 g = 58.44 g NaCl.
  2. For the reaction of X and Y: If a 12.2-g sample of X reacts with Y to form 78.9 g of XY, the mass of Y that reacted can be calculated as follows: 78.9 g - 12.2 g = 66.7 g of Y.

Evaluation of a Statement

Your friend's statement is incorrect. Even though the composition of a substance does not change during a physical change, its appearance can significantly change. For example, ice (solid water) can be crushed into flakes (physical change) while remaining H2O; hence, even with unchanged composition, its appearance differs markedly.


Learn more about changes in chemistry here:

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