Question

At room temperature, determine the appropriate phase for each of the following substances. (Look up the substance in data tables if needed.) (a) potassium chloride (c) methane (b) carbon dioxide (d) sucrose

Short answer

At room temperature, potassium chloride is solid, methane is gaseous, carbon dioxide is gaseous, and sucrose is solid.

Step-by-step solution

Determine the Phase of Potassium Chloride

Research the normal room temperature melting and boiling points of potassium chloride. The melting point of potassium chloride is about 770°C, and its boiling point is about 1420°C. Since room temperature is approximately 25°C, which is well below the melting point of potassium chloride, the substance will be in a solid phase at room temperature.

Determine the Phase of Methane

Research the normal room temperature melting and boiling points of methane. Methane has a melting point of around -182.5°C and a boiling point of about -161.5°C. Since room temperature is much higher than the boiling point of methane, the substance will be in a gaseous phase at room temperature.

Determine the Phase of Carbon Dioxide

Research the phase of carbon dioxide at room temperature. Carbon dioxide sublimes at -78°C under standard atmospheric pressure, which means it transitions directly from solid to gas without becoming a liquid. At room temperature, carbon dioxide will be found as a gas.

Determine the Phase of Sucrose

Research the melting point of sucrose. Sucrose has a melting point of about 186°C. Since room temperature is far below the melting point of sucrose, sucrose will be in a solid phase at room temperature.

Key concepts

Phase Determination

Understanding the states of matter is a fundamental aspect of chemistry and physics, and determining the phase of a substance at a given temperature is a key skill in these fields. Phase determination involves identifying whether a substance is in its solid, liquid, or gaseous state. To do this, we compare the room temperature to the known melting and boiling points of the substance. If the room temperature is below the melting point, the substance is solid. If it's between the melting and boiling points, the substance is liquid. If the room temperature exceeds the boiling point, the substance will be a gas.

To accurately determine the phase of a substance, one must consult data tables for melting and boiling points under standard conditions, which are usually 1 atmosphere of pressure and a temperature of 25°C, approximately room temperature. This process is exemplified in the exercise with substances such as potassium chloride and methane.

Melting and Boiling Points

The melting point of a substance is the temperature at which it transitions from solid to liquid, and the boiling point is where it transitions from liquid to gas. These points are characteristic physical properties and can be used to identify substances. The knowledge of melting and boiling points is vital for phase determination. For example, potassium chloride has a high melting point of about 770°C, which means it remains solid at room temperature, which is far below its melting point.

Similarly, the boiling point gives us information about when a substance will turn into a gas. Methane, with a boiling point of about -161.5°C, is a gas at room temperature, since room temperature is higher than its boiling point. Understanding these concepts provides insight into the behavior of substances in different environments and is crucial for numerous scientific and industrial applications.

Solid Phase

The solid phase is one of the three primary states of matter, and it's characterized by a fixed shape and volume. The particles in a solid are closely packed and vibrate in place, giving the substance a rigid structure. In the exercise, both potassium chloride and sucrose are solid at room temperature. Their melting points are well above room temperature, indicating that their structures remain intact and they do not flow or conform to the shape of their containers.

Identifying a solid phase involves understanding its melting point in relation to the current temperature. This aspect of the phase is vital for many practical applications, such as materials science, manufacturing, and even culinary arts, where sugar crystallization plays a crucial role.

Gaseous Phase

The gaseous phase is another fundamental state of matter where substances have neither a definite shape nor a fixed volume. Gases expand to fill their containers and are composed of widely spaced particles that move freely at high speeds. This freedom of particle movement is due to the fact that the substance's temperature is above its boiling point. Methane and carbon dioxide, for instance, exist as gases at room temperature because their boiling points are lower than room temperature. This property has implications for everything from atmospheric science to the storage and delivery of fuels.

Sublimation

Sublimation is a fascinating phase transition in which a substance moves directly from a solid to a gaseous state, without becoming a liquid. This can occur under certain conditions of temperature and pressure. Carbon dioxide, or 'dry ice', is a classic example of a substance that sublimates. At room temperature and at standard atmospheric pressure, it bypasses the liquid phase entirely. Sublimation is not only an interesting scientific phenomenon but also has practical applications, such as freeze-drying, where food is preserved by removing water content through sublimation, and in air fresheners that rely on sublimation to release fragrance into the air.