Ch Solids & Phase Changes
Solids The particles of a solid are more closely packed than those of a liquid or gas. Intermolecular forces between particles are more effective in solids compared to liquids. Attractive forces tend to hold the particles of a solid in relatively fixed positions (vibrational movement around fixed points). Properties common to solids include: definite shape and volume, high density, and incompressible.
Changes in State A phase change is the reversible physical change that occurs when a substance changes from one state of matter to another.
Changes in State A phase change is the reversible physical change that occurs when a substance changes from one state of matter to another. Classify each of these processes as endothermic or exothermic.
Heating Curves graph that illustrates the changes of state as a substance is heated. As heat is added to a solid, its temperature increases. A point is reached where the temperature levels out as heat is added. This is the point at which the solid changes to a liquid (Melting Point). Energy from the heat is used to weaken the attractive forces between the particles.
Heating Curve for Water
While a substance changes a state, its temperature does not change until the change of state is complete. Once the phase change is complete, the temperature will begin to increase as heat is added. This continues until the liquid reaches its boiling point. As the liquid changes to a gas, the temperature plateaus until the phase change is complete (Boiling point).
Heat of Fusion ( h fus ) is the amount of heat needed to melt 1 gram of a solid at its melting point. is the amount of heat released when 1 gram of liquid freezes at its freezing point. for water at 0°C H fus is 334 J/g. The quantity of heat that is absorbed during melting or released during freezing can be found using the equation: q = m H fus
Note- The Heat of Fusion equation is used only at the melting/freezing transition, where the temperature remains the same. Example Problem: How much heat is needed to melt 15.0 g of ice at 0°C?
Heat of Vaporization The heat of vaporization ( H vap ) is the amount of heat absorbed to vaporize 1 g of a liquid to gas at the boiling point. released when 1 g of a gas condenses to liquid at the boiling point. for water at 100°C H vap is 2260 J/g. The quantity of heat that is absorbed during melting or released during freezing can be found using the equation: q = m H vap
Example Problem: Calculate the amount of heat needed to convert g of liquid water to steam at 100ºC.
Outcome Sentences After reflecting on today’s lesson, complete three of the sentence starters on your note card and hand it to me as you leave today. Sentence Starters –I’ve learned… –I was surprised… –I’m beginning to wonder… –I would conclude… –I now realize that…