Question

If you lived in Alaska, state which of these natural gases you would keep in an outdoor storage tank in winter and explain why: methane \(\left(\mathrm{CH}_{4}\right),\) propane \(\left(\mathrm{C}_{3} \mathrm{H}_{8}\right),\) or butane \(\left(\mathrm{C}_{4} \mathrm{H}_{10}\right)\)

Short answer

Propane (C3H8) would be the most suitable gas to store outside in Alaska during the winter, as its boiling point of -42.1°C is comfortably lower than Alaska's average winter temperature of -17.8°C, ensuring it stays gaseous.

Step-by-step solution

Identify boiling points

Identify the boiling points of the three gases. The boiling point of methane (CH4) is -161.5°C, the boiling point of propane (C3H8) is -42.1°C, and the boiling point of butane (C4H10) is -0.5°C.

Compare boiling points with Alaskan winter temperatures

Compare these boiling points with the average winter temperature in Alaska, which is about -17.8°C. Methane would condense into a liquid form since its boiling point is lower than the average temperature. Propane, with a boiling point of -42.1°C, would remain a gas. Butane, with a boiling point of -42.1°C, would also remain in the gaseous state but with a close call.

Decide which gas to store outdoors

Considering safety and efficiency, propane would be the better choice for outdoor storage. While both propane and butane would stay gaseous, the boiling point of propane is much lower which means it would stay gaseous even during colder than average temperatures. Butane with its boiling point closer to the average winter temperature in Alaska could risk becoming liquid on colder days.

Key concepts

Methane

Methane, represented by the chemical formula \( \mathrm{CH}_4 \), is the simplest alkane and is a major component of natural gas. One of its defining characteristics is its boiling point of -161.5°C.
This is significantly lower than the average winter temperature in Alaska, which is around -17.8°C. This means methane would be a liquid in such temperatures, making it less practical for use in outdoor storage during winter.
The low boiling point of methane is attributed to its simple molecular structure, which results in weak van der Waals forces. As a result, less energy (in the form of heat) is required to convert it from a liquid to a gas. However, this also means that under typical winter conditions in cold climates like Alaska, methane condenses to a liquid state, making it challenging to use efficiently in gas form in such settings.

Propane

Propane, \( \mathrm{C}_3 \mathrm{H}_8 \), is a common fuel that is stored and used in a gaseous state. Its boiling point is -42.1°C which allows it to remain gaseous even at fairly cold temperatures, such as those found in Alaskan winters.
This low boiling point is the result of its larger molecular size compared to methane, which ensures stronger intermolecular forces. Despite requiring more energy to change states compared to methane, propane's boiling point is still sufficiently low to keep it gaseous during the winter months when average temperatures hover around -17.8°C.
Therefore, propane is often preferred for outdoor storage in cold environments. Its ability to remain a gas in sub-zero conditions ensures that it is readily available for use in heating and other applications without the risk of it becoming a liquid under normal winter temperatures.

Butane

Butane, \( \mathrm{C}_4 \mathrm{H}_{10} \), is another alkane used often for portable fuel sources. However, its boiling point is -0.5°C, which is not much lower than the freezing point of water. This makes it more susceptible to becoming liquid in cooler environments, especially in areas with average temperatures lower than its boiling point like Alaska.
The chemical structure of butane, being slightly larger than propane, results in stronger intermolecular forces, which elevates its boiling point. Though butane can still remain in a gaseous state under relatively cool conditions, the risk of it condensing to a liquid during Alaskan winters is considerable.
Therefore, when considering outdoor storage and usage in cold climates, butane is less favorable compared to propane, since it might not provide a consistent gaseous state needed for efficient fuel usage. This risk of condensation makes butane less reliable in environments with severe cold spells.