Simple Kinetic Molecular Model of Matter

1. Simple Kinetic Molecular Model of Matter Name: ________________ Class: _________________ Index: ________________

2. Learning Objectives • compare the properties of solids, liquids and gases. • infer from Brownian motion experiment the evidence for the movement of molecules. • describe qualitatively the molecular structure of solids, liquids and gases, relating their properties to the forces and distances between molecules and to the motion of the molecules. • describe the relationship between the motion of molecules and temperature. • explain the pressure of a gas in terms of the motion of the molecules. • recall and explain the following relationships using the kinetic model (stating of the corresponding gas laws is not required): • a change in pressure of a fixed mass of gas at constant volume is caused by a change in temperature of the gas. • a change in volume of a fixed mass of gas at constant pressure is caused by a change in temperature of the gas. • a change in pressure of a fixed mass of gas at constant temperature is caused by a change in volume of the gas. • use the relationships stated above to solve problems (qualitative treatment would suffice).

3. The kinetic molecular model of matter describes matter as being made up of molecules in continuous , random motion.

4. Brownian motion is the random motion of a molecule, or other very light object. It is observed by reflections of light when the object is big enough to reflect the light, as a speck of dust in a light beam, either in air or in water. We will see random movement of specks of light with the use of a microscope.The speck of dust in air is being struck at random by molecules of air, and keeps changing direction because of that. What is Brownian Motion?

5. Modern equipment to observe Brownian motion

6. Brownian motion

7. We will see random, erratic and haphazard movement of the specks of light. The molecules bombard the air particles or dust at high speeds.

8. Heat, temperature and the motion of molecules are all related. Temperature is a measure of the average kinetic energy of the molecules in a material. Heat is the energy transferred between materials that have different temperatures. Increasing the temperature increases the translational motion of molecules.

9. When heat is added to a substance, the molecules and atoms vibrate faster. As atoms vibrate faster, the space between atoms increases. The motion and spacing of the particles determines the state of matter of the substance. The end result of increased molecular motion is that the object expands and takes up more space. Mass of the object remains the same, however. Solids, liquids and gases all expand when heat is added. When heat leaves all substances, the molecules vibrate slower. The atoms can get closer which results in the matter contracting. Again, the mass is not changed.

10. Pressure in Gases From the kinetic theory of gases, a gas is composed of a large number of molecules that are very small relative to the distance between molecules. The molecules of a gas are in constant, random motion and frequently collide with each other and with the walls of any container. The molecules possess the physical properties of mass, momentum, and energy. The momentum of a single molecule is the product of its mass and velocity, while the kinetic energy is one half the mass times the square of the velocity. As the gas molecules collide with the walls of a container, as shown on the right, the molecules impart momentum to the walls, producing a force perpendicular to the wall. The sum of the forces of all the molecules striking the wall divided by the area of the wall is defined to be the pressure.

11. The Pressure Law The pressure law states that for a constant volume of gas in a sealed container the temperature of the gas is directly proportional to its pressure. This can be easily understood by visualising the particles of gas in the container moving with a greater energy when the temperature is increased. This means that they have more collisions with each other and the sides of the container and hence the pressure is increased.

12. The graph below shows the pressure of a fixed mass of gas at constant volume is directly proportional to the absolute temperature in Kelvin. p/T = constant or (p1/T1) = (p2/T2) Where T1 and T2 are the absolute temperatures, before and after the change respectively.

13. Boyle's Law Boyle's Law states that for a given mass of gas, at a constant temperature, the value of pressure multiplied by the volume is a constant.As a mathematical equation, Boyle's law is: Where P is the pressure (Pa), V the volume (m3) of a gas, and k1 (measured in joules) is the constant from this equation—it is not the same as the constants from other equations.

14. Graph of Volume against pressure

15. Boyle's Law formula P1V1=P2V2 = P3V3

16. Charles’s Law An inflatable pool float may seem quite firm as it sits on a deck in the hot sun.  However, minutes after you toss to float into the cold pool, the same float may seem under-inflated.  You may suspect that the float has developed a slow leak, but that may not be the most likely explanation for the apparent loss of air pressure.  It may be that Charles's law is responsible.   Charles's law, discovered by Jacques Charles, states that the volume of a quantity of gas, held at constant pressure, varies directly with the Kelvin temperature.  

17. Gases expand as they are heated and they contract when they are cooled.  In other words, as the temperature of a sample of gas at constant pressure increases, the volume increases.  As the temperature goes down, the volume decreases as well.  The mathematical expression for Charles's law is shown below: V1/T1 = V2/T2 Remember that Charles's law calculations must be done in the Kelvin scale.

18. Example 1 The volume of a fixed mass of gas in a cylinder is decreased at a constant temperature. Why does the pressure exerted by the molecules of the gas increase? Solution: As the volume decreases, the gas molecules strike the cylinder walls more often.

19. Example 2 The figure on the right shows some air trapped by a layer of mercury. When the beaker of water is heated, explain what happens to the layer of mercury. Solution As the temperature increases, the kinetic energy of the air molecules increases. These molecules will strike the mercury and the walls of the test tube with greater frequency. The pressure of the trapped air increases and pushes up the layer of mercury.

20. References: http://www.t2i2edu.com/WebMovie/1Chap1_files/image002.jpg http://waterocket.explorer.free.fr/images/Brownian_motionby_DavidWalkerfat_droplets.jpg http://www.chescientific.com/edu/company/EISCO/b3c326d5-c81f-4f25-8aa9-9f5f42b59ddaPH203B.jpg http://www.practicalphysics.org/imageLibrary/jpeg300/1306.jpg http://www.mansfieldct.org/schools/mms/staff/hand/atomsheat.htm http://myweb.cwpost.liu.edu/vdivener/notes/solid-liquid-gas.gif http://www.mrteverett.com/Chemistry/gases/Boyle%27s%20Law%20graph.gif http://alterniawhatif.com/HPS%20Project/Charles%27s%20Law_files/zzPL1134.jpg http://img.photobucket.com/albums/v353/dinomadkid/pressurelaw.jpg http://www.antonine-education.co.uk/New_items/STA/Gas%20Laws/Pressure1.gif