Problem 109 Which of the following demonstra... [FREE SOLUTION] (2024)

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Physical changes involve changes in the physical properties of a substance, like size, shape, or state, without altering its chemical composition.
Glass shattering is a classic example of a physical change. When a glass is shattered by a dart, its chemical makeup remains the same; it just breaks into smaller pieces.
Other examples include ice melting (change from solid to liquid) or dissolving sugar in water (sugar remains sugar, just dispersed in water).
During a physical change:

• The identity of the substance does not change.
• The change can often be reversed (e.g., water freezing and melting).
• No new substances are formed.

Understanding this is crucial for distinguishing between physical and chemical changes.

Chemical changes involve a process where one or more substances combine or break apart to form new substances.
For example, wood burning in a campfire is a chemical change. During combustion, wood reacts with oxygen to produce carbon dioxide, water vapor, and ash.
Another example is a banana turning brown. This change is due to enzymatic browning — a reaction between oxygen and phenolic compounds in the banana which produces new brown pigments.
Key characteristics of chemical changes include:

• Formation of new substances with different properties.
• Energy changes often occur (release or absorption of heat).
• Changes are usually not easily reversible.

Recognizing chemical changes is essential for understanding chemical reactions and processes.

Chemical reactions are processes that lead to the transformation of one set of substances (reactants) into another set of substances (products).
When cooking a steak in a frying pan, multiple chemical reactions occur, such as the Maillard reaction. This reaction involves amino acids and sugars combining and creating new flavor and color compounds.
Chemical reactions can be identified by:

• Change in color.
• Production of gas or odor.
• Formation of a precipitate or new substance.
• Energy exchange (heat, light).

Understanding chemical reactions helps in predicting the behavior of substances under different conditions, crucial for fields like chemistry, biology, and cooking.