Question

Which of these is an example of a physical change?

Answer 1

Answer:

b metal denting

Explanation:

Answer 2

Answer:

Choice b) Metal denting.

Explanation:

What's the difference between chemical and physical changes? In a chemical change, new substances are created. However, the types of substances stay the same in a physical change.

a)

When silver tarnishes, it reacts with a substance that contains sulfur (e.g., $\rm SO_3$) to produce silver sulfide, which is a substance different from the other two.

Before the change:

• Silver;
• A substance that contains sulfur.

After the change:

• Silver sulfide.

A new substance is created in this change. As a result, this change is chemical.

b)

When metal is dented, atoms in the metal slide past each other. The shape of the metal might change, however the substance will still be the same the metal.

Before the change:

• This particular metal.

After the change:

• This particular metal.

No substance is created. As a result, this change is physical.

c)

When iron rusts in the air, it reacts with oxygen to produce oxides of iron.

Before the change:

• Iron;
• Oxygen.

After the change:

• Oxides of iron.

Oxides of iron are created. As a result, this change is chemical.

d)

When gasoline burns in the air, it reacts with oxygen to produce water and carbon dioxide (or carbon monoxide, or both.)

Before the change:

• Gasoline;
• Oxygen.

After the change:

• Water;
• Carbon dioxide, carbon monoxide, or both.

Water and carbon dioxide/monoxide are created. As a result, this change is chemical.