Question

4
select the correct answer.
why does a solid change to liquid when heat is added?
a. the spacing between particles decreases.
b. particles lose energy.
c. the spacing between particles increases.
d. the temperature decreases.

Explanation:

When a solid changes to a liquid (melting), heat is added. This heat energy increases the kinetic energy of the particles. In a solid, particles are closely packed with fixed positions. When heat is added, particles gain energy, vibrate more vigorously, and the spacing between them increases, allowing them to move past each other, forming a liquid. Option A is incorrect as spacing increases, not decreases. Option B is incorrect because particles gain energy (not lose) when heat is added. Option D is incorrect because during melting (at the melting point), temperature remains constant until all solid is converted to liquid (for pure substances), and the added heat is used to break intermolecular forces (latent heat of fusion), so temperature doesn't decrease.

Answer:

C. The spacing between particles increases.