States of matter and kinetic theory — GCSE Chemistry practice questions

Question 1

Gallium is a soft, silvery metal. It melts at 30 °C and boils at about 2200 °C, so a piece of gallium melts when it is held in a warm hand at 37 °C.

Fig. 1 shows the arrangement of gallium atoms in three different states, P, Q and R.

Which row shows the box for gallium at 37 °C and describes the movement of its atoms?

Accepted Answer

C: Q · move around and slide past each other. 37 °C is above the melting point (30 °C) but far below the boiling point, so the gallium is a liquid. In a liquid the atoms touch in a random arrangement (box Q) and move around, sliding past each other.

Question 2

A syringe contains air. The end of the syringe is sealed and the plunger can move freely, so the pressure of the air stays the same. The syringe is put into a bowl of warm water and the plunger moves out.

Which row describes the particles in the air in the syringe as it warms up?

Accepted Answer

B: increases · stays the same · increases. Heating gives the particles more kinetic energy, so they move faster and hit the plunger harder and more often, pushing it out. The gas fills a larger volume, so the particles are further apart; the particles themselves stay the same size.

Question 3

A pure solid hydrocarbon is taken from a freezer and heated steadily until it has all turned into a gas. Fig. 1 shows how its temperature changes.

Which row describes the substance while it is boiling?

Accepted Answer

C: S to T · stays the same · overcome the forces of attraction between molecules. The first flat section (Q to R) is melting and the second (S to T) is boiling. The temperature, and so the average kinetic energy of the particles, stays the same while energy is taken in because the energy is used to overcome the forces of attraction between the molecules. The covalent bonds inside the molecules do not break.

	box	movement of the atoms
A	P	vibrate about fixed positions
B	Q	vibrate about fixed positions
C	Q	move around and slide past each other
D	R	move quickly and randomly in all directions

	average speed of the particles	size of the particles	distance between the particles
A	increases	increases	stays the same
B	increases	stays the same	increases
C	stays the same	stays the same	increases
D	decreases	stays the same	increases

	section of the graph	average kinetic energy of the particles	the energy taken in is used to
A	Q to R	stays the same	overcome the forces of attraction between molecules
B	S to T	increases	overcome the forces of attraction between molecules
C	S to T	stays the same	overcome the forces of attraction between molecules
D	S to T	stays the same	break the covalent bonds inside the molecules