Question

bell ringer

1. what are some factors that determine a chemical change has occurred?
2. what are some factors that determine a physical change has occurred?

Explanation:

1. Factors indicating a chemical change:

A chemical change involves the formation of new substances. Key indicators include:

• Color change: For example, iron rusting (iron oxide forms, color changes from silver to reddish - brown).
• Gas production (bubbling): Like in the reaction between baking soda and vinegar, carbon dioxide gas is produced.
• Precipitate formation: When two solutions are mixed and an insoluble solid (precipitate) forms, e.g., mixing silver nitrate and sodium chloride solutions forms silver chloride precipitate.
• Energy change (heat or light): Combustion reactions (like burning wood) release heat and light, and some reactions absorb heat (endothermic, e.g., mixing ammonium nitrate and water).
• Odor change: Rotting food produces a new odor due to the formation of new compounds.

A physical change does not form new substances, only changes the physical state or appearance. Key indicators include:

• Change in state (phase change): Solid to liquid (melting, e.g., ice melting to water), liquid to gas (boiling, e.g., water boiling to steam), gas to liquid (condensation, e.g., water vapor condensing to liquid water), liquid to solid (freezing, e.g., water freezing to ice), solid to gas (sublimation, e.g., dry ice - solid carbon dioxide - subliming to gas).
• Change in shape or size: Cutting a piece of paper into smaller pieces, or bending a metal wire.
• Dissolving (without chemical reaction): When sugar dissolves in water, it is still sugar (no new substance), just dispersed in water.
• Change in texture: Sanding a piece of wood changes its texture from rough to smooth.

Answer:

Some factors indicating a chemical change are color change, gas production, precipitate formation, energy change (heat/light), and odor change.

2. Factors indicating a physical change: