Chapter 5: Problem 221
Which of the following statements is wrong? (1) Evaporation is a spontaneous process (2) Evaporation is a surface phenomenon (3) Vapour pressure decreases with increases of temperature (4) Vapour pressure of a solution is less than the vapour pressure of a pure liquid
Short Answer
Expert verified
Statement (3) is incorrect.
Step by step solution
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Spontaneous Process
Evaporation is classified as a spontaneous process. This means it happens naturally and does not require any external energy input. The driving force behind evaporation is the kinetic energy of the molecules at the liquid surface.
Even at room temperature, some molecules have enough energy to break free from the liquid phase and enter the vapor phase.
This spontaneous transition occurs as the system naturally moves towards a state of higher entropy, meaning more disorder.
Because no external energy is required, evaporation is a classic example of a spontaneous process.
Even at room temperature, some molecules have enough energy to break free from the liquid phase and enter the vapor phase.
This spontaneous transition occurs as the system naturally moves towards a state of higher entropy, meaning more disorder.
Because no external energy is required, evaporation is a classic example of a spontaneous process.
Surface Phenomenon
Evaporation is specifically a surface phenomenon. This means that it involves only the molecules at the surface of a liquid.
These surface molecules are the ones that have the highest kinetic energy, allowing some to escape into the air as vapor.
Unlike boiling, which occurs throughout the entire liquid, evaporation takes place solely at the surface.
This is why you might observe water slowly disappearing from an open container but not see it boiling, as evaporation silently works at the molecular level.
Conditions like increased surface area and air flow can speed up this surface phenomenon.
These surface molecules are the ones that have the highest kinetic energy, allowing some to escape into the air as vapor.
Unlike boiling, which occurs throughout the entire liquid, evaporation takes place solely at the surface.
This is why you might observe water slowly disappearing from an open container but not see it boiling, as evaporation silently works at the molecular level.
Conditions like increased surface area and air flow can speed up this surface phenomenon.
Vapor Pressure
Vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid phase at a given temperature.
It is essential to understand that vapor pressure increases as temperature increases.
This is because higher temperatures provide more energy to the molecules, allowing more of them to escape into the vapor phase.
Therefore, the statement 'Vapor pressure decreases with increase of temperature' is incorrect.
Additionally, the vapor pressure of a solution is typically lower than that of a pure liquid due to the presence of solutes, which is explained by Raoult's law.
It is essential to understand that vapor pressure increases as temperature increases.
This is because higher temperatures provide more energy to the molecules, allowing more of them to escape into the vapor phase.
Therefore, the statement 'Vapor pressure decreases with increase of temperature' is incorrect.
Additionally, the vapor pressure of a solution is typically lower than that of a pure liquid due to the presence of solutes, which is explained by Raoult's law.
Temperature Relationship
The relationship between temperature and evaporation is critical to understand. As temperature increases:
In simple terms, higher temperatures mean faster movement of molecules, which translates to a higher rate of evaporation and an increase in vapor pressure.
This direct relationship emphasizes why boiling occurs when the vapor pressure equals the atmospheric pressure.
Understanding these relationships helps in various practical applications, such as weather forecasting and industrial processes.
- More molecules gain sufficient kinetic energy to escape the liquid
- The rate of evaporation increases
- The vapor pressure also increases
In simple terms, higher temperatures mean faster movement of molecules, which translates to a higher rate of evaporation and an increase in vapor pressure.
This direct relationship emphasizes why boiling occurs when the vapor pressure equals the atmospheric pressure.
Understanding these relationships helps in various practical applications, such as weather forecasting and industrial processes.
