Question

Choose the best answer to each of the following. Explain your reasoning with one or more complete sentences. Compared to liquid water, liquid methane is (a) colder; (b) hotter; (c) denser.

Short answer

Liquid methane is colder than liquid water.

Step-by-step solution

Analyze the Substance Characteristics

Liquid water and liquid methane both have distinct properties. Water, as we know, is a common liquid on Earth with a freezing point of 0°C and a boiling point of 100°C. Methane, a simpler organic compound, is lighter and freezes at much lower temperatures, with a liquid state typically below -160°C outside high pressure conditions.

Compare Temperature Ranges

Given the information about their typical liquid states, water remains liquid at temperatures many degrees above zero (such as room temperature), whereas methane is only liquid at extremely low temperatures below its boiling point of -161.5°C.

Evaluate Their Density

Water is denser than methane. Methane, being a light molecule, has a much lower density compared to water. This is evident from methane's behavior in gaseous state as it floats in Earth's atmosphere, while liquid water is substantially heavier, more compact and has greater intermolecular forces.

Choose the Best Answer Based on Analysis

The question asks about the conditions directly comparing to liquid water. Given the choices whether it is (a) colder, (b) hotter, or (c) denser, liquid methane, when it exists, is at a significantly colder temperature than liquid water. Therefore, the correct choice is (a) colder.

Key concepts

Temperature Comparison

When comparing the temperatures of liquid water and liquid methane, it is crucial to understand their respective states. Liquid water is common at temperatures ranging from 0°C to 100°C. Below 0°C, it freezes, and above 100°C, it boils. This temperature range encompasses most everyday conditions on Earth. On the other hand, liquid methane exists at much colder temperatures, specifically between its freezing point of about -182°C and boiling point of -161.5°C. This means that methane is only liquid at extremely low temperatures. While water is liquid at temperatures common in nature, methane needs exceptionally cold environments to remain in liquid form. Consequently, when comparing temperatures, liquid methane is significantly colder than liquid water, highlighting the major temperature differences of these substances in their liquid states.

Understanding these properties helps contextualize the conditions necessary for each liquid, assisting in determining how these substances coexist or differ in various environments.

Density Comparison

Density is a measure of how much mass is contained in a given volume. When comparing liquid water and liquid methane in terms of density, water has a clear advantage. It is denser because of the stronger hydrogen bonds between its molecules. These bonds lead to a compact arrangement, allowing water to have a higher density.

In contrast, liquid methane is composed of smaller and lighter molecules, leading to a lesser density. This lower density explains why methane, in its gaseous state, rises and disperses in the atmosphere. When the two substances are in liquid form, water’s density is noticeably higher than methane’s. This means that, in a physical context, liquid water is heavier per unit volume than liquid methane. The understanding of density differences between these two liquids also provides insights into why they behave differently under various physical conditions.

Liquid States

The liquid states of water and methane are determined by their individual physical and chemical properties. Water, due to its polar nature and hydrogen bonding, remains liquid over a broad temperature range that aligns with Earth's natural climate. This characteristic allows water to be present in ponds, lakes, rivers, and oceans, making it intrinsic to life on Earth.

Methane, however, exists in a liquid state only under specific conditions. It requires extremely cold temperatures, much below those typically found naturally on Earth. This is why methane is often stored under pressure at low temperatures to maintain its liquid state.

The concept of liquid states helps elucidate interactions in different chemical environments. Water's ability to exist in liquid form at a wide range of temperatures makes it a versatile and essential compound for biological functions. Methane's liquid state, on the other hand, is rare on Earth, often associated more with extraterrestrial environments such as Titan, Saturn's moon, where low temperatures allow for methane lakes and rivers.