# CH.5 d-f - Phase Changes

The student will investigate and understand that the phases of matter are explained by kinetic theory and forces of attraction between particles. Key concepts include:
d) phase changes;

e) molar heats of fusion and vaporization; and

f) specific heat capacity.

Bloom's Levels:  Analyze; Understand

### BIG IDEAS

• The phases of matter are determined by the proximity of molecules and energy involved in their changes.
• Energy is transferred in chemical and physical reactions.

• I can determine the time need to thaw frozen ground beef.
• I can explain why some substances  melt faster than others.

### UNDERSTANDING THE STANDARD

• Forces of attraction (intermolecular forces) between molecules determine their state of amtter at a given temperature. Forces of attraction include hydrogen bonding, dipole-dipole attraction, and London dispersion (van der Walls) forces.
• Solid, liquid, and gas phases of a substance have different energy content. Pressure, temperature, and volume changes can cause a change in physical state. Specific amounts of energy are absorbed or released during phase changes.
• A fourth phase of matter is plasma. Plasma is formed wen a gas is heated to a temperature at which its electrons dissociate from the nuclei.
• A heating curve graphically describes the relationship between temperature and energy (heat). It can be used to identify a substance's phase of matter at a given temperature as well as the temperature(s) at which is changes phase. It also shows the strength of the intermolecular forces present in a substance.
• Molar heats of fusion is a property that describes the amount of energy needed to convert one mole of a substance between its solid and liquid states. Molar heat of vaporization is a property that describes the amount of energy needed to convert one mole of a substance between its liquid and gas states. Specific eat capacity is a property of a substance that tells the amount of energy needed to raise one gram of a substance by one degree Celsius. The values of these properties are related to the strength of their intermolecular forces.

### ESSENTIALS

In order to meet this standard, it is expected that students will

d)  graph and interpret a heating curve (temperature vs. time).

interpret a phase diagram of water.

e)  calculate energy changes, using molar heat of fusion and molar heat of vaporization.

f)  calculate energy changes, using specific heat capacity.

### KEY VOCABULARY

amorphous solid, atmosphere, barometer, boiling point, calorie, calorimeter, chemical potential energy, condenstation, crystalline solid, deposition, diffusion, dipole-dipole forces, dispersion forces, ellastic collision, energy, enthalpy, enthalpy of combustion, enthalpy of reaction, entropy, evaporation, free energy, freezing point, heat, Hess's law, hydrogen bond, joule, law of conservatino of energy, law of disorder, melting point, molar enthalpy of fusion, molar enthalpy of vaporization, pascal, phase diagram, pressure, sublimation, specific heat, spontaneous process, standard enthalpy of formation, surface tension, surfactant, surroundings, system, temperature, thermochemical equation, thermohemiststry,  triple point, unit cell, universe, vaporization, vapor pressure, viscosity

Updated: Nov 19, 2017