Question

At room temperature, hydrogen can be compressed to very high pressures without liquefying. On the other hand, butane becomes a liquid at high pressure (at room temperature). What does this tell us about the critical temperatures of hydrogen and butane?

Short answer

The critical temperature of hydrogen is below room temperature, while the critical temperature of butane is above room temperature.

Step-by-step solution

Understanding Critical Temperature

The critical temperature of a substance is the highest temperature at which it can exist as a liquid, regardless of the pressure applied. Above this temperature, the substance cannot be liquefied by pressure alone.

Analyzing Hydrogen

Since hydrogen can be compressed to very high pressures without liquefying at room temperature, it indicates that its critical temperature is below room temperature. Thus, at room temperature, hydrogen is above its critical temperature and exists only as a gas, not as a liquid under high pressure.

Analyzing Butane

Butane becomes a liquid at high pressure at room temperature. This means that its critical temperature is above room temperature. At room temperature, butane can exist as a liquid if the pressure is sufficiently high.

Comparing Critical Temperatures

Since hydrogen does not liquefy at high pressures at room temperature while butane does, the critical temperature of hydrogen is lower than that of butane.

Key concepts

Phase Change of Matter

Matter can exist in various phases, including solids, liquids, and gases, and can switch between these phases through processes known as phase changes. These changes occur when energy, often in the form of heat, is absorbed or released by the substance. The phase change from a gas to a liquid is known as condensation, and it can be influenced by pressure and temperature.

For example, water vapor condenses into liquid water when it's cool enough. Critical temperature plays a pivotal role in phase changes because it is the temperature above which a gas cannot be condensed into a liquid, no matter how much pressure is applied. Understanding the critical temperature helps determine the conditions under which a substance can undergo a phase change.

Gas Liquefaction

Liquefaction of gases is a process that typically involves cooling and compressing a gas until it transitions to a liquid state. This technique is widely used in industrial applications, such as refrigeration and the production of liquefied natural gases. The critical temperature is crucial for gas liquefaction because it sets the limit to how much a gas can be cooled and compressed before it turns into a liquid.

If a gas's temperature is above its critical temperature, no amount of pressure can force it into a liquid state. On the other hand, when the temperature is below the critical point, applying sufficient pressure will result in liquefaction. This distinction is key for the storage and transportation of gases, which are often done in their liquid form to save space.

Properties of Hydrogen

Hydrogen, the simplest and most abundant element in the universe, has unique properties. It is a colorless, odorless, and highly flammable diatomic gas at room temperature. One of its significant properties related to our discussion is its low critical temperature, which is approximately -240 degrees Celsius (-400 degrees Fahrenheit).

This means that at normal environmental conditions, hydrogen exists as a gas and cannot be liquefied by pressure alone. To liquefy hydrogen, it must be cooled below its critical temperature and then compressed. Due to its properties, hydrogen is widely used in various industries, including chemical manufacturing and as a potential clean energy source in the form of hydrogen fuel cells.

Properties of Butane

Butane is a hydrocarbon belonging to the alkane series, which appears as a colorless gas at room temperature or as a liquid under pressure. It has a higher critical temperature than hydrogen, around 152 degrees Fahrenheit (67 degrees Celsius).

This property allows butane to be compressed into a liquid at room temperature, which is commonly seen in lighters and portable gas stoves. Its ease of liquefaction under pressure makes butane an ideal fuel for applications where storage space is a concern. Butane's properties such as energy density, boiling point, and non-toxicity also contribute to its widespread use in household and industrial settings.