Question

question 3 of 9
classify each of the observed changes according to whether or not they are likely to represent evidence that a chemical reaction
is occurring when performing an experiment.
may be evidence of a chemical reaction not evidence of a chemical reaction
answer bank
solution colors mixing changes in color bubbles (gas formation) precipitation
a solution color becoming less intense due to dilution explosion or fire a solid liquifying change in temperature

Explanation:

• Changes in color: Can be a sign of new substances formed in a chemical reaction. For example, rusting (iron reacting with oxygen to form iron oxide, a different - colored substance).
• Bubbles (gas formation): Indicates a gas is produced as a result of a chemical reaction. Like when baking soda reacts with vinegar to produce carbon dioxide gas.
• Precipitation: Means an insoluble solid is formed from a chemical reaction in a solution. For instance, when silver nitrate reacts with sodium chloride to form silver chloride precipitate.
• Explosion or fire: Often associated with exothermic chemical reactions (like combustion of a fuel in the presence of oxygen).
• Solution colors mixing: Just a physical mixing of substances, no new chemical species are formed.
• A solution color becoming less intense due to dilution: Only a change in concentration (a physical change), no chemical reaction.
• A solid liquifying: Melting is a physical change (change of state), not a chemical reaction.
• Change in temperature: Can be due to physical processes (like dissolving some salts in water which may absorb or release heat without a chemical reaction).

Answer:

• May be evidence of a chemical reaction: changes in color, bubbles (gas formation), precipitation, explosion or fire.
• Not evidence of a chemical reaction: solution colors mixing, a solution color becoming less intense due to dilution, a solid liquifying, change in temperature.