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How much of a triatomic gas with \(C_{V}=3 R\) would you have to add to \(6.0 \mathrm{~mol}\) of a monatomic gas to get a mixture whose thermodynamic behavior was like that of a diatomic gas?

Short Answer

Expert verified
The number of moles of the triatomic gas that needs to be added (denoted by \( n_{2} \)) is computed using the equation obtained by equating heat capacities. Find \( n_{2} \) by solving this mathematical equation.

Step by step solution

01

Define unknowns and equation

Let \( n_{2} \) be the unknown number of moles of triatomic gas that need to be added. From thermodynamics, we know that the heat capacity at constant volume \(C_{V}\), for an ideal gas, is the sum of heat capacities of all its components. Thus, we can write the equation relating the moles and specific heats of the monatomic and triatomic gases that form the mixture as: \( (n_{1} + n_{2})*C_{V,mixture}= n_{1} * C_{V,monatomic} + n_{2} * C_{V,triatomic} \). Here, \( n_{1} = 6.0 mol \) (moles of monatomic gas), \(C_{V,monatomic}=3/2*R \), \(C_{V,triatomic}=3*R \) and \(C_{V,mixture} \) is the heat capacity at constant volume for the mixture that behaves like a diatomic gas given by \(C_{V,mixture}=5/2*R \). R is the universal gas constant.
02

Substitute the values

Substitute the specified values into the equation to get the relation between \( n_{1} \) and \( n_{2} \) as: \( (6.0 + n_{2})*5/2 = 6.0*3/2 + n_{2}*3 \).
03

Solve for \( n_{2} \)

Solve the above equation for \( n_{2} \) to get the amount of triatomic gas which needs to be added.

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Key Concepts

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

Monatomic Gas
Monatomic gases are composed of single atoms. These gases are simple in structure and include substances such as helium, neon, and argon.
A key property of monatomic gases is their heat capacity at constant volume. This is represented as \( C_{V} = \frac{3}{2} R \).
Here, \( R \) is the universal gas constant. The low heat capacity is due to the limited degrees of freedom.
  • In a monatomic gas, energy is purely translational.
  • There are no vibrational or rotational contributions.
As such, they are an ideal starting point for understanding the heat capacities of more complex gases.
Triatomic Gas
Triatomic gases consist of molecules made up of three atoms. A good example of such gases is water vapor \(H_2O\).
These molecules have more complex structures due to more atoms, leading to a higher heat capacity.
The heat capacity at constant volume for a triatomic gas is \(C_{V} = 3R\).
  • In contrast to monatomic gases, triatomic gases have different modes of energy storage – translational, rotational, and vibrational.
  • These additional modes increase their ability to store energy, resulting in a higher heat capacity.
Understanding triatomic gases can help in understanding specific heat variations among other gases.
Diatomic Gas
Diatomic gases consist of molecules made up of two atoms. Examples include nitrogen \(N_2\) and oxygen \(O_2\),
which we commonly find in Earth's atmosphere.
Their heat capacity at constant volume is \(C_{V} = \frac{5}{2} R \).
This higher value compared to monatomic gases is due to:
  • Two atoms allow for translational, rotational, and some vibrational motion.
  • These motions contribute to higher energy storage.
As a result, diatomic gases often appear in diverse thermodynamic analyses, such as gas mixtures.
Ideal Gas
The Ideal Gas is a theoretical model that helps to simplify gas behavior under various conditions. This model uses several assumptions that make the equations valid.
Key points of an ideal gas include:
  • The gas particles have negligible volume compared to the container.
  • There are no intermolecular forces between the particles.
The Ideal Gas Law is represented by the equation \( PV = nRT \),
where \( P \) is pressure, \( V \) is volume, \( n \) is moles, \( R \) is the gas constant, and \( T \) is temperature.
This equation shows the relationship between these properties. The ideal gas model plays a crucial role in thermodynamics.
Thermodynamics
Thermodynamics is the branch of physics that studies energy, heat, and their transformations. It applies to various practical activities - engines, refrigerators, and even biological processes.
Some essential concepts include:
  • The First Law of Thermodynamics, focusing on energy conservation.
  • The Second Law of Thermodynamics, concerning entropy.
Heat capacity is a thermodynamic property that indicates how much energy a substance stores per degree temperature rise.
In specific scenarios, like the mix of monatomic and triatomic gases, thermodynamics aids in analyzing their energy exchange. Understanding thermodynamics allows scientists and engineers to devise methods to efficiently manage energy in systems.

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