Changes of State

GLE Objective Phase diagram of water. Sublimation Student will interpret the phase diagram of water at any given temperature and pressure. Additionally, the student will describe the behavior of solids the change directly to the vapor state and recondense to solids without passing through the liquid state.

States of Matter Plasma - typically an ionized gas. “Ionized" refers to presence of one or more free electrons. The free electrons make the plasma respond strongly to electromagnetic fields. GAS – form of matter that has no definite shape or volume; it adopts the shape and volume of it’s container. Liquid – form of matter that flows, has a fixed volume, and takes the shape of it’s container. Solid – matter that has a definite shape and volume.

Activity One activity per table For the activity Sublimation Mini-Lab Hypothesis Experimental Plan/Experiment Data Interpretations Conclusion Regarding Hypothesis Supported Not Supported Contradicted Answer the questions at the end of the lab on the lab sheet provided, put the lab in your journal

Activity Carefully watch the air freshener pieces and the cup.

Sublimation Instructor will heat solid Iodine in a beaker Materials Heating Plate Beaker Solid Iodine Discuss observations

Sublimation Sublimation is useful in many situations and processes. Freezing freshly brewed coffee and removing the water vapor with a vacuum pump makes freeze-dried coffee. Carbon Dioxide (dry ice) has a very low temperature of -78oC and does not produce a liquid when it melts – keeps food dry during shipping. The naphthalene in mothballs changes into a vapor without going through the liquid state.

Phase Diagrams The relationships among the solid, liquid, and vapor states (or phases) of a substance in a sealed container are best represented in a single graph called a phase diagram. A phase diagram gives the conditions of temperature and pressure at which a substance exists as solid, liquid, and gas (vapor).

Phase Diagram of Water What key ideas do you see represented by this phase diagram?

Phase Diagram of Water Convert the temperatures to oF and the pressures to psi.

Phase Diagram A unique feature of the diagram is the point at which all three curves meet. This meeting point, called the triple point, describes the only set of conditions at which all three phases can exist in equilibrium with one another. For water the triple point is 0.016oC and 0.61 kPa (0.0060 atm). What happens when boiling and melting are carried out at pressures greater and less than 101.3 kPa? The diagram also shows why ice melts under the blades of the skates and forms a lubricant, enabling skaters to glide smoothly over the ice!