Phase Changes “It’s just a phase” States of Matter Solid, liquid and gas (plasma and BEC). Changes between states are called “phase changes”. Caused by a change of heat or pressure. More often heat. HEAT and TEMPERATURE are not the same thing. Temperature Measures the average kinetic energy of the particles in a substance. Is measured in Celsius or Kelvin. Kinetic energy is directly related to the speed of the molecules. The faster the particles/molecules are moving the higher the temperature. Heat Heat is a measure of energy (Joules). HEAT and TEMPERATURE are not the same thing. Ex. A cold Lake Superior has more heat energy than a boiling pot of water. For our class, higher temperature means more heat. Solids Molecules are tightly packed together. High potential energy – more bonds. Molecules greatly affected by intermolecular forces. Particles vibrate in place. Very Dense. Not easily compressed. Liquids Particles are not so tightly packed (liquids flow and can be poured). Medium potential energy. Particles are affected by intermolecular forces. Tension-ability of a liquid’s molecules to “stick” together. Adhesion-stick to other compounds Cohesion- stick to self Surface Cool Videos Number One Number Two Number Three Gases Particles spread out as the container will allow. High kinetic energy, particles are moving very quickly (1000 km/sec). Little effect of intermolecular forces. Low density, can be compressed, very fluid. Cool Videos Number Two Phase Changes When a substance changes states. Requires the input or the removal of energy or change in pressure. During a phase change the temperature does not change, but the amount of energy does. Phase Change Diagram. Intermolecular Forces Interactions between particles that cause them to “stick” together. Strongest in solids Weakest in gases. Strongest when particles move slowly. During a phase change IMF are either weakened or strengthened. Sublimation Transformation of a substance to a gas from a solid state with no liquid transition. Dry Ice does this. Deposition When a gas transforms into a solid without transitioning through a liquid state. Ex. Frost forming on windows. Where does all the energy go? During a phase change energy is added, but the temperature does not increase. The energy goes toward breaking up weak intermolecular forces between the particles. Some Vocab Triple Point: Pressure and temperature where a substance exists as a solid, liquid, and gas. Critical Point: Indicates critical temp and pressure. Critical Temperature The temperature at and above which no additional pressure can be added to maintain a liquid. The critical pressure is the highest pressure that will keep a compound a liquid at the critical temperature. The two correspond to a point on a graph. Helpful Info Melting point and freezing point are the same thing. It just depends if the substance is getting hotter or colder. During a phase change temperature does not change, but the amount of heat does. Intermolecular Forces Intermolecular Forces are the forces of attraction that are between molecules. This is why lakes form lakes, gold can be melting together, and why any matter can be held together. Phases Phases is the term scientist use to more properly define solid, liquids and gases. It means the same as the term “state” Phase is defined as “a part of matter that has uniform properties through out the entire substance” Phases change As scientists we can change phases. We can change a solid into a liquid and a liquid into a gas. When two phases exist at the same time it is called equilibrium. Equilibrium is a dynamic condition in which two opposing changes occur in equal rates in a closed system Equilibrium To have equilibrium we need to have both a temperature and pressure. When we have both a measured temperature and pressure two or three states will exist at the same time. Ice melting into water, water freezing into ice. Phase Diagrams Scientist have phase diagrams to show exactly the temperature and pressure must be achieved to have a solid, liquid, gas, two phases or all three phases A phase diagram by definition is “a relationship between physical states that deals with temperature and pressure.” Phase diagram of water. Pressure is in atmopheres (normal pressure is 1 atm) Temperature is in celcius (water boils at 100) Each of the lines represent equilibrium (two states exist at the same time) Point C is called the critical point Critical point: is the point on which liquids and gases are indistinguishable (can’t tell the difference Point A is called the Triple Point The Triple point is the temperature and pressure in which gas, liquid and solid all exist in equilibrium Video Sublimation Freezing Freezing Waves Vapor Pressure The molecules in a liquid are constantly moving and running into each other. Sometimes they will “bounce” out of the container they are in. As a result, a faint vapor will exist over most liquids. Vapor Pressure Vapor Pressure is the pressure of vapor over a liquid at equilibrium with the atmosphere. When water boils the vapor pressure exceeds the atmospheric pressure and the molecules leave the liquid with little impediment. Vapor Pressure So then how do puddles evaporate and why can clothes dry outside when the temperature is below freezing??? Water molecules are always moving and are always escaping from their container. Heat makes them move faster or slower.