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Chapter 15: Problem 80

The molar enthalpy of fusion of methanol is 3.22 \({kJ} / {mol}\) . What does this mean?

Short Answer

Expert verified
The molar enthalpy of fusion of methanol (3.22 kJ/mol) represents the amount of heat energy required to convert one mole of methanol from its solid state to its liquid state at a constant temperature. This means that 3.22 kJ of heat energy are needed to change one mole of methanol from the solid phase to the liquid phase.

Step by step solution

01

Definition of molar enthalpy of fusion

Molar enthalpy of fusion, or simply enthalpy of fusion, represents the amount of heat energy required to convert one mole of a substance from the solid state to the liquid state without changing its temperature. It is a measure of the heat absorbed by the substance during the phase transition from solid to liquid, and it is usually expressed in units of kilojoules per mole (kJ/mol).
02

Interpreting the given molar enthalpy of fusion for methanol

We are given that the molar enthalpy of fusion of methanol is 3.22 kJ/mol. This means that it takes 3.22 kJ of heat energy to change one mole of methanol from its solid state to its liquid state at a constant temperature. This value helps determine the heat energy required for melting a specific amount of methanol, which can be calculated using the following mathematical expression: Heat energy = (molar enthalpy of fusion) x (number of moles) In conclusion, the given molar enthalpy of fusion of methanol indicates that 3.22 kJ of heat energy are needed to convert one mole of methanol from its solid phase to its liquid phase at a constant temperature.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Heat Energy
Heat energy, often simply called heat, is a form of energy that is transferred between substances or systems due to a temperature difference. In the context of the molar enthalpy of fusion, heat energy plays a critical role. It is the energy required to change the state of a substance without altering its temperature at the melting point.
  • When substances absorb heat energy, their temperature generally rises. However, during phase transitions like melting, the absorbed heat energy is used to break the bonds that hold the particles together in a solid.
  • This is why even though energy is being added, the temperature does not change. The energy is devoted entirely to changing the phase.
  • In the example of methanol's molar enthalpy of fusion being 3.22 kJ/mol, this is the amount of heat energy needed to change one mole of methanol from solid to liquid at its melting point.
Understanding heat energy in this context provides insight into how much energy is needed to induce phase transitions without temperature changes.
Phase Transition
Phase transition refers to the process where a substance changes from one state of matter to another. In the case of molar enthalpy of fusion, the phase transition of interest is from solid to liquid.
  • During a phase transition, the temperature of a substance remains constant even though heat energy is being added. This is because all the heat energy goes into breaking the intermolecular forces rather than increasing kinetic energy.
  • For methanol, undergoing a phase transition from solid to liquid requires 3.22 kJ/mol of energy. This indicates a relatively low energy demand, characteristic of substances with weaker intermolecular forces.
  • Knowing the energy requirements of a phase transition helps predict the amount of energy needed to facilitate the change for a given amount of substance.
Phase transitions are fundamental in understanding how substances switch between different states and the energy dynamics involved in these processes.
Solid to Liquid
The process of changing from a solid to a liquid is a specific type of phase transition known as melting. This process is essential for understanding how energy affects the structural change of matter.
  • The melting process occurs at a constant temperature termed the melting point, where the solid's structured molecules begin to move more freely to form a liquid.
  • Using methanol as an example, it requires 3.22 kJ of heat energy per mole to transition from solid to liquid at this melting point.
  • Understanding the solid to liquid transition is vital for fields ranging from chemistry to material science, as it influences material properties and behaviors under different temperatures.
Appreciating the process of melting helps us grasp the energy requirements and structural changes involved as a substance changes its state.

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Most popular questions from this chapter

Challenge Define a new energy unit, named after yourself, with a magnitude of one-tenth of a calorie. What conversion factors relate this new unit to joules? To Calories?

Describe how you would calculate the amount of heat absorbed or released by a substance when its temperature changes.

Explain how perspiration can help cool your body.

Determine \(\Delta H_{\text { comb }}^{\circ}\) for butanoic acid, \(\mathrm{C}_{3} \mathrm{H}_{7} \mathrm{COOH}(1)+5 \mathrm{O}_{2}(\mathrm{g}) \rightarrow 4 \mathrm{CO}_{2}(\mathrm{g})+4 \mathrm{H}_{2} \mathrm{O}(\mathrm{l})\) Use data in Table \(\mathrm{R}\) -11 on page 975 and the following equation. \(4 \mathrm{C}(\mathrm{s})+4 \mathrm{H}_{2}(\mathrm{g})+\mathrm{O}_{2}(\mathrm{g}) \rightarrow \mathrm{C}_{3} \mathrm{H}_{7} \mathrm{COOH}(1) \Delta H=-534 \mathrm{kJ}\)

Which of these reactions would you expect to be spontaneous at relatively high temperatures? At relatively low temperatures? Explain a. \(C H_{3} O H(1) \rightarrow C H_{3} O H(g)\) b. \(C H_{3} O H(g) \rightarrow C H_{3} O H(1)\) c. \(C H_{3} O H(s) \rightarrow C H_{3} O H(1)\)
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