Kinetic Theory of Matter Flashcards
Using ideas of molecular theory, explain why a liquid has definite volume but no definite shape.
The intermolecular forces of a liquid are weaker than a solid, and the molecules vibrate thus a liquid has no definite shape. However, the intermolecular forces are still strong enough to hold the molecules together in the liquid and prevent them from moving away from one another, thus a liquid has definite volume.
A student conducts an experiment to observe the behaviour of dust
particles when placed in an illuminated glass cell. Under the microscope, the dust particles were observed to be moving randomly. Explain why.
The dust particles are constantly bombarded by air particles which are in random and continuous motion.
Predict the motion of particles if temperature were to increase. Explain.
The motion becomes faster and more vigorous. The average kinetic energy of the particles increases hence they experience greater resultant force.
In terms of molecular properties, explain how air in a sealed cylinder exerts pressure on the walls of the cylinder.
Air molecules are in random and continuous motion. When air molecules collide with the inner walls of the cylinder continuously, they exert forces on the walls. The average force per unit area exerted is the pressure of the cylinder.
In terms of molecular properties, explain why pressure in a sealed cylinder increases when temperature increases.
There is an increase in energy in the internal store of gas molecules and the kinetic energy of gas molecules increases. With greater energy, there is more frequent collisions of the gas molecules onto the walls of the cylinder, thus the force exerted on the cylinder increases and the average force per unit area exerted increases.
In terms of molecular theory, explain why a piece of iron expands when heated.
Energy is transferred to the particles in the iron. The particles vibrate more vigorously and they become further apart from one another, hence the iron expands.
In terms of molecular energy, explain why the temperature of a piece of iron does not increase when it starts melting.
Energy supplied is used to overcome the intermolecular forces between the molecules. The average kinetic energy of the molecules remains the same while the average potential energy increases. Thus, temperature remains constant during melting.
