High School Chemistry : Phases of Matter

Study concepts, example questions & explanations for High School Chemistry

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Example Questions

Example Question #5 : Phase Diagrams And Transitions

Which of the following occurs during vaporization?

Possible Answers:

Atoms get closer together and form a more rigid shape

Atoms become spaced further away from each other

Atoms disappear and are destroyed

Atoms become highly organized in patterns

Correct answer:

Atoms become spaced further away from each other

Explanation:

Vaporization refers to the phase change from liquid to gas, also known as evaporation. When becoming a gas, atoms spread out and expand to fill whatever container they are in. Conservation of mass hold that atoms are never created nor destroyed. Atoms becoming more organized and forming a more rigid shape describes a phase change toward becoming solid.

 

Example Question #6 : Phase Diagrams And Transitions

The transition from a solid to a gas is known as __________.

Possible Answers:

sublimation

deposition

an impossible process

evaporation

Correct answer:

sublimation

Explanation:

Some substances will transition from a solid to a gas and skip the liquid phase entirely at standard conditions. This change from a solid to a gas is called sublimation. The reverse process of a gas going to a solid is known as deposition. As an example, solid carbon dioxide (dry ice) will sublimate to produce gaseous carbon dioxide at room temperature.

Evaporation is the process by which a liquid transitions to a gas.

Example Question #7 : Phase Diagrams And Transitions

Under which of the following conditions would ice be most likely to sublimate?

Possible Answers:

High temperature and low pressure

Low temperature and high pressure

High temperature and high pressure

Low temperature and low pressure

Correct answer:

High temperature and low pressure

Explanation:

Sublimation refers to the phase change whereby a substance goes directly from solid to gas. At high temperature and pressure water will be more likely to melt and than evaporate. At low temperature and low pressure, the water will likely stay solid. Likewise at low temperature and high pressure. At high temperature and low pressure, the ice will be most likely to sublimate. This is clear if one looks at the phase diagram for water. High pressure makes it energetically favorable for water to melt before evaporating. Keeping the pressure low, however, makes it more favorable to pass straight into the gaseous phase.

 

 

Example Question #8 : Phase Diagrams And Transitions

Which of the following is not a phase transition?

Possible Answers:

Fusion

Deposition

Condensation

Sublimation

Decomposition

Correct answer:

Decomposition

Explanation:

There are six phase changes possible. Transition from solid to gas is sublimation, while transition from gas to solid is deposition. Transition from solid to liquid is melting, while transition from liquid to solid is fusion (freezing). Transition from gas to liquid is condensation, while transition from liquid to gas is vaporization (boiling). Each phase transition is considered a physical change, not a chemical change, because the identity of the compound remains unchanged.

Decomposition is a reaction type that involves a reactant being broken down into two or more products. This is a chemical change, since the identity of the reactant is changed.

Example Question #1 : Help With Phase Diagrams

Heating curves are used to graph the change in temperature as heat is added to a system. A solid system is heated until it is converted to a gas, and the heating curve is graphed. Why does the heating curve have two horizontal plateaus?

Possible Answers:

Temperature does not increase during a phase change

These are times in the experiment when the scientists stopped heating the substance

This is a scientific error that has been created in the heating curve

Heat does not increase during a phase change

The plateaus show when the substance is getting warmer

Correct answer:

Temperature does not increase during a phase change

Explanation:

A heating curve shows the transition of a solid to a liquid to a gas. A solid, liquid, or gas can exist within a range of varying temperatures, but when a solid is turning into a liquid, or a liquid is turning into a gas, the temperature stays constant. This is the point at which there is a mixture of solids and liquids or liquids and gases within the system. Heat is still being applied to the system, but instead of raising the temperature the heat is converting from one phase to another. Temperature will remain constant during a phase transition until all of the substance has been converted to the final phase.

Example Question #1 : Phase Diagrams And Transitions

What phase is determined by the inability to distinguish liquid from gas?

Possible Answers:

It is always possible to distinguish gases from liquids

Nanocritical gas

Supercritical gas

Nanocritical fluid

Supercritical fluid

Correct answer:

Supercritical fluid

Explanation:

A phase diagram is used to show what phases of a certain compound exist at given temperatures and pressures. Decreasing pressure and increasing temperature generally cause the compound to favor the gaseous phase, while increasing pressure and decreasing temperature generally cause the compound to favor the solid phase.

On a phase diagram, there is a point known as the critical point. This point gives coordinate at which gases and liquids stop being distinguishable from one another. If pressure or temperature is increased above this point, the sample will enter a state that is fluid, but is neither gas nor liquid. Remember that both gases and liquids have fluid properties. This state of matter is known as a supercritical fluid.

Example Question #51 : Phases Of Matter

On an energy diagram for water, in which temperature is graphed against energy input, the temperature of liquid water will increase up to . At this point, the temperature will plateau even as more energy is added. After this brief plateau, the temperature of the water will rise above .

What value is given by the length of this plateau along the x-axis?

Possible Answers:

Enthalpy of vaporization

Enthalpy of freezing

Enthalpy of fusion

The specific heat capacity of water

Correct answer:

Enthalpy of vaporization

Explanation:

Upon reaching , the temperature of the water will stop increasing and stay at for a brief time. At this point, the energy being added to the water is being used to break the intermolecular bonds between the water molecules. Once the bonds are broken, the water will have fully entered the gas phase, and the water vapor will continue to increase in temperature.

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 #52 : Phases Of Matter

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?

Possible Answers:

Standard pressure is above the pressure of carbon dioxide's triple point

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

Standard temperature is the critical temperature for carbon dioxide

Correct answer:

Standard pressure is below the pressure of carbon dioxide's triple point

Explanation:

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 #53 : Phases Of Matter

What does critical temperature describe?

Possible Answers:

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 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 at which a solution will boil

Correct answer:

Critical temperature describes the temperature above which it is impossible to liquify a gas, even if pressure is applied

Explanation:

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.

Example Question #1 : Using The Ideal Gas Law And Combined Gas Law

Which of the following is a condition of the ideal gas law?

Possible Answers:

The gas molecules must adhere to the container wall

The gas molecules must interact with each other

The gas molecules must be moving at a slow speed

The gas molecules must be in specific mole ratios

The gas molecules do not have volume

Correct answer:

The gas molecules do not have volume

Explanation:

The ideal gas law has some conditions that must be met, conditions that certainly cannot be met in the real world. These conditions include that the gases cannot interact with one another, gases must be moving in a random straight-line fashion, gas molecules must not take up any space, and gases must be in perfect elastic collisions with the walls of the container. These conditions minimize the effect that gas molecules have on one other, allowing a prediction based on completely random and unimpeded molecular movement. In reality, these conditions are impossible. All real gas molecules have a molecular volume and some degree of intermolecular attraction forces.

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