Lesson 1 Kinetic Theory of Matter Liceo Da Procida What is Kinetic Theory? It sounds so scary! But its not! Kinetic theory of matter just means that matter is made up of atoms that are ALWAYS moving Even if something is standing perfectly still, the atoms inside it are still moving! Does this rock look like its moving? It is! Kinetic Theory The reason you cant see the movements is that the atoms are moving at a smaller-than- microscopic level In the big rock, the atoms are barely moving at all, but theyre vibrating back and forth Depending on how much the atoms in an object are moving, we have different states of matter (solid, liquid, gas) Concept Question Do you think the molecules in a solid or liquid move faster? (Think: which state of matter seems like its particles would be more separate/have more room to move?) A) The molecules in the solid move faster B) The molecules in the liquid move faster Concept Question Do you think the molecules in a solid or liquid move faster? (Think: which state of matter seems like its particles would be more separate/have more room to move?) A) The molecules in the solid move faster B) The molecules in the liquid move faster Concept Question Do you think the molecules in a liquid or gas move faster? (Think: which state of matter seems like its particles would be more separate/have more room to move?) A) The molecules in the liquid move faster B) The molecules in the gas move faster Concept Question Do you think the molecules in a liquid or gas move faster? (Think: which state of matter seems like its particles would be more separate/have more room to move?) A) The molecules in the liquid move faster B) The molecules in the gas move faster Phase Changes We generally heat an object up or cool it down to make it change phase When a substance is melting or boiling, the temperature stays constant, even though were adding heat. Where does that heat go? Phase Changes The heat is used to pull molecules apart from each other, thus changing their phase! The heat of fusion is the amount of heat required to convert a solid to a liquid The heat of vaporization is the amount of heat required to convert a liquid to gas Concept Question For this substance, is the heat of fusion or heat of vaporization greater? A) Heat of fusion B) Heat of vaporization Phase Changes So we have: Solid Liquid Gas Slower molecules >Faster molecules Colder >Hotter So what does adding heat do to molecules? Phase Changes Higher temperature = more heat = faster molecules = molecules are farther apart Solid: Very orderly Liquid: A little more room for movement Gas: Free for all Phase Changes Does this make sense? When youre sweaty on a hot day, do you want to huddle with your friends or be as far apart as possible? What about on a cold day? What do penguins do in the winter? Phase Changes You are like an atom! The hotter you are, the further apart you are from your fellow atoms Solids Liquids Kinetic Theory of a Gas Gases have a bit more leeway than solids and liquids Molecules can be very far apart from each other, and theyre always moving quickly What is Pressure? Pressure is a measure of how much individual atoms are pushing on the sides of a container in a gas More collisions = higher pressure If you pump air into a container that cant get any bigger, would the pressure increase or decrease? Reminder: Concept Question As you raise the temperature in a gas, the molecules move: A) Faster B) Slower C) No speed change D) Sideways. Reminder: Concept Question As you raise the temperature in a gas, the molecules move: A) Faster B) Slower C) No speed change D) Sideways. Appletll Kinetic Gas Equation Kinetic Energy = 1.5 k*T k = Boltzmanns constant = 1.38 x J/K CAREFUL! Temperature must be in Kelvin Kinetic Gas Equation The kinetic gas equation just means that the kinetic energy is higher at higher temperatures In other words, molecules move faster at higher temperatures we already know that! We sometimes talk about the root mean square velocity, which is the square root of the average velocity (using KE = 0.5 mv 2 and the kinetic gas equation, we get v rms = sqrt(v) = sqrt(3kT/ m)) Root mean square velocity = rms speed Practice Problems Remember: v rms = sqrt(3kT/ m) k = 1.38 x J/K 1)The rms speed of molecules in a gas at 20C is to be increased by 2 percent. To what temperature must it be raised? 2)If the temperature of an ideal gas is raised from 25C to 100C, how many times faster is the rms speed of the gas molecules? Fun Videos Phase change experiment Playing with liquid nitrogen