A scientist is performing an experiment on a
powder. Which of the following is a sign that a chemical change has definitely occurred during his experiment?
The powder catches on fire.
The powder releases bubbles.
The powder heats up.
The powder breaks apart into smaller particles.
a yes
b yes
c either
d no
c can be either. If it heats up because you built a fire under it that is a physical change. If it heats up because of the experiment being conducted it is a chemical change.
The answer is A :D
A sign that a chemical change has definitely occurred during the scientist's experiment is when the powder catches on fire.
The correct answer is "The powder catches on fire." This is because catching fire is an indication that a chemical change has occurred. When a substance catches fire, it usually means that it is undergoing a combustion reaction, where new substances are formed as a result of the chemical reaction. In this case, the powder is changing its chemical composition by reacting with oxygen in the air and releasing heat and light in the process.
To determine which one of the given options is the correct answer, you need to understand the concept of chemical changes and signs of their occurrence. Chemical changes involve the rearrangement of atoms and molecules to form new substances with different properties from the original ones. There are several common signs that can indicate a chemical change has taken place:
1. Formation of a gas: The powder releasing bubbles indicates the formation of a gas as a byproduct of a chemical reaction. This can be an indication of a chemical change, but it is not a definitive sign as some physical changes can also release gas.
2. Release or absorption of heat: The powder heating up indicates that energy is being released, which is often associated with chemical reactions. However, it is important to note that heating alone is not enough evidence to confirm a chemical change, as some physical changes can also lead to a rise in temperature.
3. Color change: A change in color can indicate a chemical change. For example, if the powder changes color during the experiment, it could suggest that a chemical reaction has taken place.
4. Formation of a precipitate: If the powder forms a solid substance that settles at the bottom of the container, it could indicate the formation of a new substance, called a precipitate. This can suggest a chemical change.
In the given options, only the powder catching on fire is a definitive sign that a chemical change has occurred. The other options, such as the release of bubbles or heating up, can provide some evidence, but they are not definite indicators on their own. It is important to consider multiple factors and observations to draw conclusions about chemical changes.