Question

Draw the general shape of the temperature-energy graph for the heating of ethanol from \(-120^{\circ} \mathrm{C}\) to \(120^{\circ} \mathrm{C}\). (Given: \(\left.\mathrm{Mp}=-117.3^{\circ} \mathrm{C} ; \mathrm{Bp}=78.5^{\circ} \mathrm{C}\right)\)

Short answer

The graph has upward-sloping segments with flat sections at melting and boiling points.

Step-by-step solution

Understanding the Problem

We need to sketch the temperature-energy graph for ethanol as it is heated from \(-120^{\circ} \mathrm{C}\) to \(120^{\circ} \mathrm{C}\). The given melting point (Mp) is \(-117.3^{\circ} \mathrm{C}\) and the boiling point (Bp) is \(78.5^{\circ} \mathrm{C}\). These points indicate where phase changes occur.

Identifying the Key Points

The heating process involves several segments:1. Solid ethanol from \(-120^{\circ} \mathrm{C}\) to the melting point \(-117.3^{\circ} \mathrm{C}\).2. Melting process at \(-117.3^{\circ} \mathrm{C}\).3. Liquid ethanol from \(-117.3^{\circ} \mathrm{C}\) to the boiling point \(78.5^{\circ} \mathrm{C}\).4. Boiling process at \(78.5^{\circ} \mathrm{C}\).5. Gaseous ethanol from \(78.5^{\circ} \mathrm{C}\) to \(120^{\circ} \mathrm{C}\).

Drawing the Graph

Start the graph from \(-120^{\circ} \mathrm{C}\). Draw an upward sloping line to represent the heating of solid ethanol until the melting point at \(-117.3^{\circ} \mathrm{C}\). At \(-117.3^{\circ} \mathrm{C}\), the line should flatten to show the melting process (constant temperature, increasing energy). Continue with another upward line from \(-117.3^{\circ} \mathrm{C}\) to \(78.5^{\circ} \mathrm{C}\) to show heating of liquid ethanol. At \(78.5^{\circ} \mathrm{C}\), draw another flat line to depict the boiling process.Finally, draw an upward sloping line from \(78.5^{\circ} \mathrm{C}\) to \(120^{\circ} \mathrm{C}\) for gaseous ethanol.

Key concepts

Heating Curve

A heating curve is a fascinating graph that represents how heat energy affects a substance's temperature over time. These graphs help in understanding the phase transitions of materials as they absorb heat. In a typical heating curve, you'll start heating the substance from a cold temperature, slowly watching as it makes its way through different phases—solid, liquid, and gas.

For ethanol, these changes occur at specific temperatures due to its unique properties. As you increase energy by heating, you'll notice that the temperature rises until it hits specific points where phase changes occur. This results in several distinct sections on the graph where each section represents a different phase or transition:

• Starting from a solid state, it follows an upward slope until the melting point.
• When it reaches the melting point, the graph flattens since temperature remains constant during melting even though energy is still being absorbed.
• Next, the line ascends again as the liquid ethanol heats up further, leading to the boiling point.
• Again, the graph levels off as the boiling process takes place, where energy input changes the liquid to a gas at constant temperature.
• Finally, the graph rises sharply once more as the gaseous phase increases in temperature.

This cycle vividly demonstrates the fascinating interplay between energy and the physical states of ethanol.

Melting Point

The melting point of a substance is a key characteristic that defines when it transitions from a solid to a liquid. For ethanol, this critical temperature occurs at \(-117.3^{\circ} \mathrm{C}\). At this point, ethanol absorbs heat but its temperature doesn't immediately change. Instead, the energy goes into breaking the bonds that hold its molecules in a solid structure.

This phase transition is crucial on a heating curve graph. You will observe a flat line as ethanol melts, indicating that despite continued energy input, the temperature remains steady until the phase change is complete. This behavior occurs because all incoming energy is utilized to overcome intermolecular forces rather than raise the temperature. In real-world applications, knowing a substance’s melting point aids in determining storage conditions and material handling needs, especially for those working in chemical and materials engineering fields.
Preparing for these shifts ensures operational and storage efficiencies and helps prevent damage or degraded functionality due to unexpected phase changes.

Boiling Point

The boiling point is another critical temperature for a substance, symbolizing the transition from liquid to gas. In the case of ethanol, this occurs at \(78.5^{\circ} \mathrm{C}\). Like the melting point, there is no change in temperature during boiling despite continued heating. Instead, the energy is used to break attractive forces in the liquid, allowing molecules to disperse and form a gas.

On a phase change graph, you will notice this as another flat segment—highlighting no temperature rise during this transformation. Understanding boiling points is particularly important in fields like distillation, where separating components through heating relies on differing boiling points.

The ability to predict how and when a substance will boil under specific conditions is fundamental in designing processes that are efficient and safe. Ethanol's relatively low boiling point compared to water makes it an excellent candidate for various applications in industries ranging from perfumes to fuel production.

Ethanol Properties

Ethanol is a versatile compound with unique properties that make it useful across numerous industries. It is a volatile, flammable, clear liquid commonly referred to as alcohol used in beverages, sanitizers, and as a biofuel. Among its key properties are its distinct melting and boiling points, and its ability to mix with both water and organic compounds, making it an excellent solvent.

Identifying how ethanol behaves under different temperatures is crucial for leveraging its chemical characteristics. For example, due its boiling point being just\(78.5^{\circ} \mathrm{C}\), ethanol vaporizes more rapidly than water, which aids in specific extraction techniques and in its effective use as a cleaning agent, leaving surfaces residue-free.

Additionally, knowing its low melting point of \(-117.3^{\circ} \mathrm{C}\) can help industry professionals understand potential storage and transport considerations, especially in colder climates. Ethanol’s properties must be considered carefully in pharmaceutical applications, where purity and systematic behavior under varying environmental conditions are pivotal. These properties, when correctly harnessed, are what enable ethanol to support diverse industrial advancements.