University:
University of Cambridge
Course:
0470 IGCSE | History
Academic year:

2023
Views:

27

Pages:

5
Author:

anon

IGCSE Coordinated Science: Molecular Model 1. Describe qualitatively the molecularstructure of solids, liquids and gases. Solids ■ Particles are close together, help together by strong intermolecular forces. ■ Particles vibrate around a fixed point, so has little freedom of movement. Liquids ■ Particles are also quite close together, but the forces are not as strong as that of those in solids. ■ The liquid takes the shape of its container. Gases ■ Particles are far apart from each other and bounce around randomly in the container. ■ Intermolecular forces between particles are pretty weak. 2. Relate the properties of solids, liquids and gases to the forces and distances between molecules and to the motion of the molecules Solid Distance between particles are very close together, as witnessed by the diagram above. Liquid The distance here is not as close as that of the solids, but the particles are still quite close together, and the forces between the particles are still quite strong. A liquid, because the particles can move and slide over each other, liquids fill the shape of its container. Gas Particles are very far apart here. Again, this can be seen through the diagram. Because particles are not in place, gases can flow like a liquid. 3. Interpret the temperature of a gas in termsof the motion of its molecules. The temperature of a substance is proportional to the kinetic energy of the molecules. If the temperature of the gas increases, it will have more kinetic energy ,and will move around faster and obviously, particles will have more energy. 4. Describe qualitatively the pressure of a gasin terms of the motion of its molecules. Firstly, what is pressure? Pressure is the force exerted by a substance per unit area on another substance. Let’s take a balloon as an example. If you blow into a balloon, the balloon expands because there is a greater pressure inside the balloon than outside. So, how can we describe pressure in terms of molecules? The motion of molecules in a substance causes the collision of these molecules on the wall of the container. This exerts a force on the walls of this container, which we define as pressure. 5. Describe qualitatively the effect of a changeof temperature on the pressure of a gas atconstant volume. Let’s use a quantitative description to describe this: PV = nRT Let’s forget about nR here, so what we’re dissecting is basically: PV = T PV = T Volume is constant So as we can see from this formula, Pressure and Temperature are proportional. We call this relation the Gay Lussac’s Law If the gas has more kinetic energy in its molecules, pressure increases as it hits the container with more kinetic energy. If you decrease the volume of the container, the pressure increases as the number of particles hitting each cm3 of the container wall will increase. Look at the diagram below: The particles are hitting the containers randomly. And you have to admit, there is quite alot of wall-space for the particles to hit at. The Pressure here is quite low as we can see that the number of particles that will hit the walls of container each second will not be too high (low frequency), and that is how we determine pressure. However, what happens when we decrease the volume by half? The particles are definitely going to hit the walls of the container more frequently, so the pressure is going to increase.