39. Which of the following is always true of a chemical change?
Answer: C
A new substance is formed.
A chemical change is characterized by the formation of one or more new substances, which is a fundamental aspect of such changes in chemistry.
A) Color, shape, or texture is altered.
While a chemical change can involve alterations in color, shape, or texture, these changes are not definitive indicators of a chemical change. Physical changes can also result in alterations of these properties without any new substances being formed.
B) Mass is increased.
This statement is misleading as the mass of a substance in a closed system remains constant during a chemical reaction, according to the law of conservation of mass. Therefore, mass is not necessarily increased in a chemical change.
C) A new substance is formed.
This is the defining feature of a chemical change. During a chemical reaction, the reactants undergo a transformation to create new substances with different properties, making this option correct.
D) Gas or vapor is generated.
Although the generation of gas or vapor can occur during some chemical changes, it is not a universal characteristic. Not all chemical changes produce gas or vapor, making this statement incorrect.
Conclusion
The formation of a new substance is the only statement that is always true of a chemical change, distinguishing it from physical changes. While other options may occur during some chemical reactions, they do not universally apply, confirming that option C is the correct answer.