Two common signs that a chemical change has occurred?

Two common signs that a chemical change has occurred?

• A. A new substance forms with different properties
• B. A color change or gas bubbles are observed
• C. A new substance forms with different properties and a color change or gas bubbles are observed
• D. No reaction occurs

Answer: (C)

When a chemical change happens, matter is transformed into substances with different properties. You also often see visible clues, such as a color change or the appearance of gas bubbles, indicating a new substance is being formed. So the strongest way to recognize a chemical change is that a new substance forms and there are noticeable signs like color change or gas evolution. If you only have one sign, it’s still a clue, but the combination of a new substance plus these visible indicators is the most reliable indication. If nothing changes, or if the change is purely physical, you wouldn’t expect new substances to appear or gas to bubble up.

When a chemical change happens, matter is transformed into substances with different properties. You also often see visible clues, such as a color change or the appearance of gas bubbles, indicating a new substance is being formed. So the strongest way to recognize a chemical change is that a new substance forms and there are noticeable signs like color change or gas evolution. If you only have one sign, it’s still a clue, but the combination of a new substance plus these visible indicators is the most reliable indication. If nothing changes, or if the change is purely physical, you wouldn’t expect new substances to appear or gas to bubble up.