Question

question 12 of 20
points: 5

which model shows a chemical change taking place and which shows a physical change? how can you tell?

Explanation:

• Model A: In a chemical change, new substances are formed. In model A, the starting substance (represented by the red - colored molecules at the bottom) is different from the products (the red - and - green and red - only molecules). The bonds within the original molecules have been broken and new bonds have been formed to create different molecular structures.
• Model B: In a physical change, the chemical composition of the substance remains the same. In model B, the molecules before and after the change are of the same type (all green - colored molecules). Only the arrangement or state (if we assume this is a state - change like from liquid to gas, but based on molecular models, it's about molecular identity) of the molecules has changed, not their chemical identity.

Answer:

• Model A shows a chemical change because new types of molecules (with different compositions) are formed.
• Model B shows a physical change because the type of molecules remains the same.