Distinguish between physical and chemical changes and provide examples of each.

here's the answer to question 4:

A physical change is a type of change in which the form of matter is altered but its chemical identity remains the same. No new substances are formed, and the change is often reversible.

A chemical change (or chemical reaction) is a type of change in which one or more substances are converted into different substances with new chemical properties. New substances are formed, and the change is generally irreversible.

Here's a differentiation with examples:

• Physical Change:

  • Definition: Alters the form or appearance of a substance but does not change its chemical composition.
  • Key characteristic: No new substance is formed.
  • Example: Melting ice. When ice (solid water) melts, it becomes liquid water. Both are still $\text{H}_2\text{O}$, just in a different physical state. Other examples include dissolving sugar in water, cutting paper, or boiling water.

• Chemical Change:

  • Definition: Results in the formation of one or more new substances with different chemical properties.
  • Key characteristic: New substances are formed.
  • Example: Burning wood. When wood burns, it reacts with oxygen to produce ash, carbon dioxide, and water vapor. These are entirely new substances with different properties from the original wood. Other examples include rusting of iron, cooking an egg, or digestion of food.