Which observation most likely indicates that only one chemical change has taken place?1 The change cannot be reversed.2 The shapes changes 3states of matter 4changes a reaction occurs.
The observation that most likely indicates that only one chemical change has taken place is that the change cannot be reversed.
The correct answer is 1: The change cannot be reversed.
To understand why this observation indicates that only one chemical change has taken place, we need to define what a chemical change is. A chemical change, also known as a chemical reaction, occurs when substances are transformed into different substances with different chemical properties. This usually involves the breaking and formation of chemical bonds.
In this case, if the change cannot be reversed, it means that the original substances have undergone a permanent transformation into new substances. This is a characteristic of a chemical change. When a chemical change occurs, the resulting substances usually have different properties compared to the original substances, and the change cannot be easily reversed by physical means (e.g., heating, cooling, dissolving).
Let's analyze the other answer options to see why they are not the most likely indication of a chemical change:
2: The shape changes: Changes in shape of a substance are usually related to physical changes rather than chemical changes. Physical changes do not involve the formation of new substances; they only affect the physical state or appearance of a substance (e.g., melting, freezing, bending).
3: States of matter: Changes in states of matter (transition from solid to liquid, liquid to gas, etc.) are also primarily physical changes. Although chemical reactions can cause changes in states of matter, they usually involve multiple chemical changes occurring simultaneously.
4: Changes a reaction occurs: This option seems incomplete or unclear. However, if we assume it means "a reaction occurs," it could refer to any type of reaction, including physical or chemical reactions. Without further context, it is challenging to determine if a chemical change has specifically taken place.
In summary, when observing that a change cannot be reversed, it strongly suggests that a chemical change has occurred.