High School Chemistry : Phase Diagrams and Transitions
Study concepts, example questions & explanations for High School Chemistry
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Example Questions
Example Question #11 : Phase Diagrams And Transitions
On an energy diagram for water, in which temperature is graphed against energy input, the temperature of liquid water will increase up to 
What value is given by the length of this plateau along the x-axis?
Enthalpy of vaporization
Enthalpy of fusion
The specific heat capacity of water
Enthalpy of freezing
Enthalpy of vaporization
Upon reaching 
The amount of heat needed to break the intermolecular bonds is called the enthalpy of vaporization. During the plateau, heat is being added and immediately used to break bonds. The length of the plateau corresponds to the amount of heat added during this period, which will equal the enthalpy of vaporization.
Example Question #12 : Phase Diagrams And Transitions
Carbon dioxide does not have a liquid phase under standard conditions. Instead, it transitions from a solid to a gas as temperature increases. Based on this information, which of the following statements is true?
Standard pressure is below the pressure of carbon dioxide's triple point
Standard pressure is above the pressure of carbon dioxide's triple point
Standard temperature is the critical temperature for carbon dioxide
Standard pressure is equal to the pressure of carbon dioxide's triple point
Standard pressure is below the pressure of carbon dioxide's triple point
The triple point of a compound refers to the temperature and pressure conditions under which a substance exists in all three phases of matter simultaneously. If the pressure is below that of the triple point, the compound will only exist as a solid or a gas, depending on the temperature of the compound. As a result, standard pressure is below carbon dioxide's triple point since it cannot exist as a liquid.
Example Question #5 : Help With Phase Diagrams
What does critical temperature describe?
Critical temperature describes the temperature at which a liquid becomes a solid
Critical temperature describes the temperature at which organic compounds become inorganic
Critical temperature describes the temperature at which an element becomes radioactive or toxic
Critical temperature describes the temperature above which it is impossible to liquify a gas, even if pressure is applied
Critical temperature describes the temperature at which a solution will boil
Critical temperature describes the temperature above which it is impossible to liquify a gas, even if pressure is applied
A phase diagram is divided into three regions based on temperature and pressure conditions. Solids exist at low temperatures and high pressures. Liquids exist at medium temperatures and relatively high pressures. Gases exist at high temperatures and low pressures. The lines dividing each region show the conditions required to change between phases, such as the boiling point or freezing point of the compound.
The critical point, or critical temperature, refers to the terminal point on the segment that divides the liquid and gas regions of the phase diagram. Beyond this point, liquids and gases become indistinguishable. The critical point occurs at a very high temperature and pressure. Increasing the termperature beyond this point cannot result in a phase change, regardless of pressure change.
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