Kinetic Particle Model of Matter: Physics 0625 (Cambridge O Level / IGCSE)

Solids, liquids and gases can be compared in terms of how far apart their particles are, on average. Which list puts the three states of matter in order of increasing average particle separation, from smallest to largest?

A student sets up a smoke cell and shines light into it, so that smoke particles floating in the air inside the cell appear as tiny bright specks when viewed through a microscope.

(a) Describe how the smoke particles are seen to move when viewed through the microscope. [2]

(b) Explain, in terms of the particles of the surrounding air, why the smoke particles move in this way. [2]

(c) State what this observation provides evidence for. [1]

A rigid, sealed metal cylinder contains a fixed mass of gas. The volume of the cylinder does not change. The gas starts at a temperature of $17\text{°C}$ and is then heated until its temperature reaches $47\text{°C}$.

(a) Convert $17\text{°C}$ to a temperature in kelvin. [1]

(b) Explain, in terms of the motion of the gas particles, why the pressure of the gas increases as it is heated from $17\text{°C}$ to $47\text{°C}$ at constant volume. [3]

(c) State the value, in degrees Celsius, of absolute zero, and describe the motion of the gas particles at this temperature. [2]

A sealed syringe contains a fixed mass of gas at a pressure of $1.2\times10^{5}\text{ Pa}$ and a volume of $60\text{ cm}^3$. The temperature of the gas is kept constant while the piston is pushed in, reducing the volume to $40\text{ cm}^3$.

(a) Explain, in terms of the motion of the gas particles, why the pressure of the gas increases as it is compressed at constant temperature. [2]

(b) Calculate the new pressure of the gas. [3]

(c) Describe, in words, the relationship between the pressure and the volume of a fixed mass of gas at constant temperature, as shown by the equation $pV = \text{constant}$. [1]

Smoke particles suspended in air are observed through a microscope, moving in a continuous, random zig-zag path. Which statement correctly explains this motion?

A pure solid substance is heated steadily until it just melts. Which statement correctly describes what happens to its particles during melting?

A small block of solid wax is heated slowly in a test tube. It first melts to form a liquid, and heating is then continued until the liquid wax boils to form a gas.

(a) Describe how the arrangement of the wax particles changes as the solid wax melts. [2]

(b) Describe how the motion of the wax particles changes as the liquid wax is heated further, up to the point where it boils. [2]

(c) State how the average spacing between the wax particles changes when the liquid boils to form a gas. [1]

A sealed syringe containing only air can have its plunger pushed in, noticeably reducing the volume of air inside. In contrast, a solid metal rod of the same mass cannot be compressed into a smaller volume, no matter how hard it is squeezed.

(a) Using the kinetic particle model, explain why the air in the syringe can be compressed so much more easily than the solid metal rod. [3]

(b) The mass of air in the syringe does not change as the plunger is pushed in. State and explain what happens to the density of the air as its volume is reduced. [2]

(c) Suggest why a liquid, like a solid, is very difficult to compress. [1]

A scuba diving cylinder contains compressed air at a pressure of $2.0\times10^{7}\text{ Pa}$ in a volume of $12\text{ dm}^3$. All of this air is released, at constant temperature, into a large empty flexible bag at atmospheric pressure, $1.0\times10^{5}\text{ Pa}$. No air is lost during the transfer.

(a) Explain, in terms of the motion of the air particles, why the pressure of the air is so much lower once it is in the bag. [2]

(b) Calculate the volume occupied by the air once it is in the bag. [3]

(c) State the two conditions that must apply to the air for the equation $pV = \text{constant}$ to be used in part (b). [1]

A fixed mass of gas is kept at a constant temperature. Its pressure, $p$, is measured for several different volumes, $V$, and a graph of $p$ (on the y-axis) against $\dfrac{1}{V}$ (on the x-axis) is plotted. What is the shape of this graph?