Question

The melting point of chloroform is \(-64{ }^{\circ} \mathrm{C}\) and its boiling point is \(61^{\circ} \mathrm{C}\). Sketch a heating curve for chloroform from \(-100^{\circ} \mathrm{C}\) to \(100^{\circ} \mathrm{C}\) a. What is the state of chloroform at \(-75^{\circ} \mathrm{C}\) ? b. What happens on the curve at \(-64{ }^{\circ} \mathrm{C}\) ? c. What is the state of chloroform at \(-18^{\circ} \mathrm{C}\) ? d. What is the state of chloroform at \(80^{\circ} \mathrm{C}\) ? e. At what temperature will both solid and liquid be present?

Short answer

a) Solid b) Solid and liquid mixture c) Liquid d) Gas e) -64°C

Step-by-step solution

- Identify Key Points

Mark the melting point (-64°C) and boiling point (61°C) of chloroform on a temperature axis ranging from -100°C to 100°C.

- Sketch the Heating Curve

Draw the heating curve with three distinct regions: solid, liquid, and gas. Start from -100°C (solid phase), transition through melting at -64°C to reach the liquid phase, continue heating until it boils at 61°C, and then move into the gas phase up to 100°C.

- Determine State at -75°C

Since -75°C is below the melting point (-64°C), chloroform is in the solid state.

- Analyze Curve at -64°C

At this temperature (-64°C), chloroform is transitioning from solid to liquid, so it will be a mixture of both solid and liquid states.

- Determine State at -18°C

-18°C is above the melting point (-64°C) and below the boiling point (61°C), thus chloroform is in the liquid state.

- Determine State at 80°C

Since 80°C is above the boiling point (61°C), chloroform will be in the gas state.

- Identify Temperature for Solid and Liquid

Both solid and liquid phases of chloroform coexist at the melting point, which is -64°C.

Key concepts

Melting Point

The melting point is the temperature at which a substance changes from a solid to a liquid.
For chloroform, this occurs at \( -64^{\circ}C \).
At this temperature, the particles in the solid structure gain enough energy to break free and move into a liquid state.
The formula to represent the melting point is simple: at this temperature, the solid and liquid states are in equilibrium.
This means that both phases can coexist—like a block of ice slowly turning into water but with some frozen sections still present.

Boiling Point

The boiling point is the temperature where a liquid changes into a gas.
For chloroform, this temperature is \( 61^{\circ}C \).
At this stage, the liquid particles gain enough energy to escape into the vapor phase.
When a substance reaches its boiling point, it transforms from liquid to gas throughout the entire liquid, not just on the surface.
This is why you see vigorous bubbling during boiling—it's the formation of vapor bubbles inside the liquid that rise to the surface and burst.

Heating Curve

A heating curve is a graph that shows how the temperature of a substance changes as it absorbs heat.
For chloroform, the curve starts at \( -100^{\circ}C \) (solid state), going through the melting point at \( -64^{\circ}C \) to become a liquid.
It continues to rise showing the increase in temperature of the liquid until it reaches the boiling point at \( 61^{\circ}C \).
After that, the curve represents the conversion from liquid to gas until reaching \( 100^{\circ}C \).
This type of curve is important because it shows the different phase transitions and the constant temperature regions during melting and boiling.

Phase Transition

Phase transition refers to the change of a substance from one state of matter to another.
During this transition, energy is absorbed or released, but the temperature remains constant.
When chloroform melts at \( -64^{\circ}C \), it undergoes a transition from solid to liquid.
Similarly, at \( 61^{\circ}C \), it transitions from liquid to gas.
Phases can also coexist at specific temperatures, such as solid and liquid at the melting point.
Understanding phase transitions helps predict how a substance behaves under different temperature conditions.

Temperature

Temperature measures the average kinetic energy of particles in a substance.
It's a crucial factor in determining the state of matter—solid, liquid, or gas.
For example, at \( -75^{\circ}C \), chloroform is a solid because it's below the melting point.
At \( -18^{\circ}C \), it's in a liquid state as it's between the melting and boiling points.
Finally, at \( 80^{\circ}C \), chloroform is a gas since it's above the boiling point.
Temperature influences phase transitions by providing or removing the necessary energy required for these changes.