How Materials Change State

Question 1

A heating curve for water shows a flat horizontal segment at 0 °C while solid ice is turning into liquid water. Which statement best explains why the temperature stays constant during this flat segment?

Accepted Answer

The added heat energy is used to break the intermolecular forces between the particles, so their average kinetic energy (temperature) does not increase.

Answer

The added heat energy is lost to the surrounding air, preventing the temperature from rising.

Answer

The particles stop moving during the change of state, so the temperature remains the same.

Answer

The water molecules chemically react to form a new substance at that temperature, keeping the temperature constant.

Question 2

Why does ice float on liquid water?

Accepted Answer

In ice, water molecules are arranged in an open hexagonal lattice that keeps them farther apart, making ice less dense.

Answer

In ice, the particles are packed more tightly than in liquid water, so ice is more dense.

Answer

In ice, the particles attract each other more strongly, pulling them together and increasing the density.

Answer

In ice, water molecules move faster than in liquid water, causing them to spread out and lower the density.

Question 3

Which of the following best explains why ice is less dense than liquid water?

Accepted Answer

In the solid state, water molecules form a crystal lattice that keeps them farther apart than in the liquid, so ice occupies a larger volume for the same mass.

Answer

During freezing, the water molecules stop moving completely, which makes the ice expand.

Answer

When water freezes, the molecules move faster, pushing them farther apart.

Answer

Freezing causes water molecules to become heavier, increasing the volume of the ice.

Try three questions

A heating curve for water shows a flat horizontal segment at 0 °C while solid ice is turning into liquid water. Which statement best explains why the temperature stays constant during this flat segment?

Why does ice float on liquid water?

Which of the following best explains why ice is less dense than liquid water?

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