Which scenarios are definite signs that a chemical reaction has occurred?
_(Select all that apply)_
Water is heated and releases a gas.
Blue and yellow paint mix to make green paint.
A piece of iron begins to rust.
Two liquids are mixed together and release a light.
A and C?
I interpreted A this way. A chemical reaction produces heat which boils the water enough to produce steam. The production of heat shows the presence of a chemical reaction.
I agree with D as yes.
umm ... boiling water releases a gas , no chemical reaction
... dissolved gases come out of solution , then the water goes to steam
a release of light indicates an energy change
... powered by a reaction
Yes, that is correct. The definite signs that a chemical reaction has occurred in the given scenarios are:
- Water is heated and releases a gas (Option A): This is an example of a chemical reaction called evaporation in which water molecules gain energy from heating and change into a gaseous state, known as water vapor.
- A piece of iron begins to rust (Option C): When iron reacts with oxygen in the presence of moisture, it undergoes a chemical reaction called rusting. Rust formation is a clear indication that a chemical reaction has occurred.
Blue and yellow paint mixing to make green paint (Option B) does not involve a chemical reaction. It is a physical change where two different colored paint mix together to produce another color.
Two liquids being mixed together and releasing light (Option D) does not necessarily indicate a chemical reaction. It could be due to a physical process, such as luminescence, where the release of light is a result of energy being emitted, rather than a chemical reaction taking place.
To identify signs of a chemical reaction, it is important to look for the formation of new substances, changes in color, formation of precipitates (solid particles), evolution or absorption of heat, release of gas, or emission of light or sound.