Question

A substance, \(X\), has the following properties: Sketch a heating curve for substance \(\mathrm{X}\) starting at \(-50 .{ }^{\circ} \mathrm{C}\).

Short answer

The heating curve of substance X can be sketched as follows: 1. Start with a sloping line from the initial temperature of \(-50^{\circ} \mathrm{C}\) (solid phase) to the melting point at \(16^{\circ} \mathrm{C}\). 2. Draw a horizontal line at the melting point temperature (\(16^{\circ} \mathrm{C}\)) representing the phase change from solid to liquid. 3. Continue with a sloping line representing the temperature increase of the liquid phase until the boiling point at \(84^{\circ} \mathrm{C}\). 4. Draw a horizontal line at the boiling point temperature (\(84^{\circ} \mathrm{C}\)) representing the phase change from liquid to gas. 5. Label the starting temperature (\(-50^{\circ} \mathrm{C}\)) and the melting and boiling points (\(16^{\circ} \mathrm{C}\) and \(84^{\circ} \mathrm{C}\), respectively) on the y-axis.

Step-by-step solution

Determine the starting phase of the substance

First, we should determine the initial phase of the substance at the starting temperature of \(-50^{\circ} \mathrm{C}\). Since the temperature is below the melting point of substance X (\(16^{\circ} \mathrm{C}\)), the substance must be in the solid phase at the beginning.

Sketching the initial heating phase

Next, we need to sketch the initial heating phase. Since the substance starts at a temperature of \(-50^{\circ} \mathrm{C}\) and it is in the solid phase, we draw a sloping line representing the increase in temperature of the solid substance until the temperature reaches the melting point at \(16^{\circ} \mathrm{C}\).

Sketching the melting phase

Once the temperature reaches the melting point (\(16^{\circ} \mathrm{C}\)), the substance will start to change its phase from solid to liquid. During this phase change, the temperature remains constant until the entire substance transitions to the liquid phase. We sketch this by drawing a horizontal line at the melting point temperature on the heating curve.

Sketching the liquid phase heating

After the solid substance has entirely melted, it will continue to heat up in the liquid phase. This will be a sloping line on the heating curve, representing the increase in temperature of the liquid substance until it reaches the boiling point at \(84^{\circ} \mathrm{C}\).

Sketching the boiling phase

Once the temperature reaches the boiling point (\(84^{\circ} \mathrm{C}\)), the substance will start to change its phase from liquid to gas. Similar to the melting phase, during the boiling phase, the temperature remains constant until the entire substance transitions to the gaseous phase. We sketch this by drawing a horizontal line at the boiling point temperature on the heating curve.

Indicate starting and critical temperatures on the curve

Finally, we should label the initial temperature of \(-50^{\circ}C\) on the y-axis at the starting point of the heating curve. Also, label the y-axis with the melting and boiling points of the substance at \(16^{\circ}C\) and \(84^{\circ}C\), respectively. Following these steps, you will have successfully sketched the heating curve of substance X.

Key concepts

Phase Changes

Phase changes refer to the transformation of a substance from one state of matter to another, such as solid to liquid or liquid to gas. During these changes, the substance absorbs or releases energy, often in the form of heat. It's essential to understand the different types of phase changes:

• Melting: Transition from a solid to a liquid.
• Freezing: Transition from a liquid to a solid.
• Boiling: Transition from a liquid to a gas.
• Condensation: Transition from a gas to a liquid.
• Sublimation: Direct transition from a solid to a gas.
• Deposition: Direct transition from a gas to a solid.

These changes are depicted on a heating curve as horizontal lines, indicating that the temperature remains constant while the substance's state changes. This happens because the absorbed or released energy is used to break or form bonds between molecules without increasing the kinetic energy of the molecules, which means that the temperature stays stable.

Melting Point

The melting point of a substance is the temperature at which it transitions from a solid to a liquid. At this temperature, the solid's particles have enough kinetic energy to overcome their fixed positions and begin to move more freely past each other, adopting the properties of a liquid.

On a heating curve, the melting point is represented by a flat horizontal line. This indicates that even though heat is being added to the system, the temperature does not rise until the whole substance has melted. At its melting point, both solid and liquid phases coexist in equilibrium. This principle is essential in determining the thermal characteristics and stability point of substances in various applications. Knowing the melting point is crucial for industries such as pharmaceuticals, where precise temperature conditions are vital for the effectiveness and stability of compounds.

Boiling Point

The boiling point is the temperature at which a liquid turns into a gas. When a liquid reaches this temperature, the vapor pressure of the liquid equals the external pressure surrounding the liquid, allowing bubbles of vapor to form within the liquid. These vapor bubbles rise to the surface and escape into the air.

On a heating curve, the boiling point is indicated by another flat horizontal line where the temperature remains constant. During boiling, heat energy is absorbed and used to break intermolecular forces and turn the liquid into a gas, instead of increasing temperature. This phase equilibrium between liquid and gas shows how energy is consumed in phase transitions rather than in temperature increase.

Understanding the boiling point is critical for various processes such as distillation and cooking, as it determines how substances behave when heat is applied. It's also essential in scientific applications where precise temperature control can influence the chemical reactions and stability of substances.