Kinetic Molecular Theory, Gases Kinetic Molecular Theory, Pressure, and Volume

States of Matter, Kinetic Molecular Theory Read 9.1 (pages 418 – 420) Are there larger attractive forces between molecules of gases, liquids, or solids? Explain. Which state(s) of matter have these properties: a) definite shape, b) definite volume, c) takes the shape its container, d) incompressible. Explain the properties of the three states of matter by referring to the forces that exist in each (e.g. “solids have intermolecular forces that are so strong that molecules are fixed in place. This gives solids a definite shape and volume. Solids are incompressible because their strong forces hold molecules tightly together, eliminating space between molecules.” Repeat for liquids & gases.)

States of Matter, Kinetic Molecular Theory What factor, in addition to strength of intermole-cular forces, affects the state of a substance? Which theory deals with molecular motion? What 3 types of motion can a molecule exhibit? Simply stated, what do these words mean? Which types exist in solids, liquids, & gases? What term means “the energy of motion”? What is an average measure of this? A flask of O2(g) is heated from 10°C to 90°C. Are all O2 molecules moving faster at 90°C? Explain. Why does evaporation cause the temperature of a liquid to decrease? Would a gas diffuse faster or slower in a vacuum? Explain your reasoning.

Solids have greater attractions, that’s why they stay together (whereas gases disperse). a) solids, b) solids & liquids, c) liquids & gases, d) solids & liquids. Liquids have forces that are strong enough to keep their molecules together (thus, they are incompressible with a definite volume). However, these forces are not strong enough to fix molecules in place (shape is not fixed) Gases have forces so weak that, at room temperature, molecules move freely (shape & volume change). The large spaces between molecules makes gases compressible.

Temperature affects state. The kinetic molecular theory. 1- vibrational (small motion from side to side), 2- rotational (spinning), 3- translational (straight line motion). Solids: vibrational, Liquids: all, Gases: mostly translational, also rotational (and vibrational). Kinetic energy is the energy of motion. Temperature = average kinetic energy Not all molecules will be faster. However, the average speed will increase.

Only the fastest moving molecules are able to overcome the attractive forces of their neighbors and leave the surface of the liquid. The slower molecules are left behind. Thus the average kinetic energy (i.e. temperature) decreases. Gas particles travel in a straight line until they hit another particle. A vacuum is devoid of molecules, so particles of a gas placed in a vacuum will not bump into anything until they hit the side of the container. Thus, a gas will diffuse faster in a vacuum.

Demo 1: Diffusion of KMnO4 Observations: KMnO4 (potassium permanganate) diffuses faster in hot water. Explanation: KMnO4 dissolves in water. As the KMnO4 dissolves, it collides with H2O molecules and spreads out. Because molecules in hot water are moving faster, the solid dissolves faster and diffuses faster. Cold water Hot water

Demo 3: Heating Mercury Observations: beads are propelled upwards when mercury is heated. Explanation: heat increases the kinetic energy, so that the particles move faster. The fastest moving mercury molecules (that boil off) transfer their energy to the beads, causing them to jump. Would this work with water? Air Glass tube Beads Mercury Heat source

Pressure and Volume Read 9.2 (pages 423 – 425) Define pressure. What is the SI unit for pressure? How does a gas exert pressure on the side of a container? What would happen to the pressure if a container of gas was heated? Explain with reference to the kinetic molecular theory). Define and give the conditions of STP and SATP. How was atmospheric pressure first determined? Copy figure 1 into your notes. What would happen to the the level of mercury if a) the barometer were at a high elevation (where atmospheric pressure is lower), b) the tube length was doubled, c) the air pressure was increased? Solve for question 2 on page 425.

Pressure and Volume Force per unit area. SI unit is Pa (kPa) Pressure is due to collisions of gas particles. Pressure would increase because the speed of molecules increases ( collisions per second) STP: standard temperature and pressure (0°C, 101.3 kPa or 1 atm). SATP: standard ambient temperature and pressure (25°C, 100 kPa). Via an inverted tube of mercury (see fig 1) a) the level of mercury is lower (<760 mm Hg) b) no change: it’s the air pressure that pushes mercury up, not the vacuum that pulls it up. c) the Hg level would rise (“barometer rising”) Q: how can you get water from a well over 10 m?

For more lessons, visit www.chalkbored.com Demo 4: Kill da wabbit Question: what will happen when the air pressure surrounding a balloon is decreased? Why? Explanation: A balloon normally stays the same size because the pressure inside the balloon is equal to the pressure outside the balloon (rate of collisions with the wall of the balloon is equal). Reducing the pressure on the outside eliminates opposing collisions, allowing the balloon to expand. For more lessons, visit www.chalkbored.com

Demo 2: thermal expansion of a liquid Observations: coloured water moves slowly up the tube Explanation: heat increases the kinetic energy of liquid particles. The particles move faster (greater vibrational, rotational, and translational energy). This greater movement increases the distance between molecules. Thus, the volume expands. Glass tube Rubber stopper Coloured water in florence flask Hot plate