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At what temperature is the speed of sound in helium (ideal gas, \(\gamma=1.67,\) atomic mass \(=4.003\) u) the same as its speed in oxygen at \(0^{\circ} \mathrm{C} ?\)

Short Answer

Expert verified
The temperature is approximately 727°C.

Step by step solution

01

Understand the speed of sound formula

The speed of sound in an ideal gas is given by the formula \( v = \sqrt{\frac{\gamma \cdot R \cdot T}{M}} \), where \( v \) is the speed of sound, \( \gamma \) is the adiabatic index, \( R \) is the universal gas constant (8.31 J/(mol·K)), \( T \) is the temperature in Kelvin, and \( M \) is the molar mass of the gas.
02

Determine speed of sound in oxygen at 0°C

For oxygen, we have \( M_{O_2} = 2 \times 15.9994 = 32.00 \) g/mol, \( \gamma = 1.4 \), and the temperature \( T_{O_2} = 273 \) K. Substitute these into the formula to find the speed of sound in oxygen: \( v_{O_2} = \sqrt{\frac{1.4 \times 8.31 \times 273}{0.032}} \). Calculate this to find the speed of sound in oxygen.
03

Equate helium speed of sound to that of oxygen

We want the speed of sound in helium at temperature \( T \) to match that of oxygen at 0°C. Setting \( v_{He} = v_{O_2} \), we use \( \gamma_{He} = 1.67 \) and \( M_{He} = 4.003 \) g/mol. The equation becomes: \( \sqrt{\frac{1.67 \times 8.31 \times T}{0.004003}} = v_{O_2} \). Square both sides for simplicity: \( \frac{1.67 \times 8.31 \times T}{0.004003} = v_{O_2}^2 \). Solve for \( T \).
04

Calculate the temperature for helium

Using the result from Step 3, solve for temperature \( T \):\( T = \frac{v_{O_2}^2 \times 0.004003}{1.67 \times 8.31} \). Substitute \( v_{O_2} \) from Step 2 and perform the calculation to get \( T \).
05

Convert and interpret final answer

The calculated \( T \) is in Kelvin. Convert \( T \) to Celsius by subtracting 273.15. This value represents the temperature at which the speed of sound in helium matches that in oxygen at 0°C.

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Key Concepts

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

Ideal Gas Law
The Ideal Gas Law is a fundamental principle in science that relates the pressure, volume, temperature, and quantity of an ideal gas. It's expressed as \( PV = nRT \), where \( P \) is pressure, \( V \) is volume, \( n \) is the amount of substance in moles, \( R \) is the universal gas constant, and \( T \) is temperature in Kelvin.

In the context of calculating the speed of sound in gases, the Ideal Gas Law helps us understand how temperature influences speed. Increased temperature typically means increased kinetic energy of the gas particles, leading to faster sound propagation. This derived understanding of the gas's thermal dynamics is fundamental in applying the speed of sound formula. By knowing the relationships expressed in the Ideal Gas Law, students can comprehend why the speed of sound changes with temperatures and different gases.

Here, we observe these applications in determining the equivalent speed of sound between helium and oxygen under varying temperature conditions.
Adiabatic Index
The adiabatic index, often symbolized as \( \gamma \), describes the relationship between the capacities of gases to do work and their heat capacity. In simpler terms, it shows how the pressure of the gas relates to its volume under adiabatic conditions (no heat transfer occurs).

For gases like helium and oxygen, \( \gamma \) is crucial since it helps compute the speed of sound. The speed of sound formula \( v = \sqrt{\frac{\gamma \cdot R \cdot T}{M}} \) includes \( \gamma \), showing its importance in determining how fast sound waves travel through a gas. For helium, \( \gamma \) is approximately 1.67, reflecting its unique properties as a monoatomic gas. On the other hand, for diatomic gases like oxygen, \( \gamma \) is generally lower, around 1.4.

By understanding \( \gamma \), students can see why sound travels at different speeds in various gases. It provides insight into molecular structure and kinetic behaviors, essential for physics and chemistry applications.
Temperature Conversion
Temperature conversion, especially from Celsius to Kelvin and vice versa, is a pivotal part of many scientific calculations. The Kelvin scale is the standard measuring scale for temperature in scientific contexts because it starts at absolute zero, the theoretical point where molecular motion stops.

In this exercise, temperatures had to be converted from Celsius to Kelvin. This involves a straightforward addition of 273.15 to the Celsius measurement. For instance, to find the speed of sound in oxygen at 0°C, it's necessary to use 273 K in calculations. Conversely, converting back to Celsius is needed when interpreting the final answer to understand real-world conditions.

Mastering these temperature conversions ensures that calculations using thermodynamic principles, like those for gas speed of sound, remain accurate and meaningful.
Molar Mass
Molar mass is the weight of one mole of a given substance. It plays a significant role in chemical reactions and processes as it helps determine the mass of various substances required or produced. Molar mass is expressed in grams per mole (g/mol).

For calculating the speed of sound in gases, molar mass is an integral part of the formula \( v = \sqrt{\frac{\gamma \cdot R \cdot T}{M}} \). Here, \( M \) is the molar mass, influencing the speed of sound based on the gas's molecular weight. Lighter gases typically have higher speeds of sound due to their lower molar mass, as seen with helium's 4.003 g/mol compared to oxygen's 32.00 g/mol.

Understanding molar mass clarifies why different gases exhibit varying speeds of sound and aids comprehension of their physical properties and reaction tendencies.

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Most popular questions from this chapter

Using an intensity of \(1 \times 10^{-12} \mathrm{W} / \mathrm{m}^{2}\) as a reference, the threshold of hearing for an average young person is 0 dB. Person 1 and person 2 , who are not average, have thresholds of hearing that are \(\beta_{1}=-8.00 \mathrm{dB}\) and \(\beta_{2}=+12.0 \mathrm{dB}\). What is the ratio \(I_{1} / I_{2}\) of the sound intensity \(I_{1}\) when person 1 hears the sound at his own threshold of hearing compared to the sound intensity \(I_{2}\) when person 2 hears the sound at his own threshold of hearing?

A middle-aged man typically has poorer hearing than a middle-aged woman. In one case a woman can just begin to hear a musical tone, while a man can just begin to hear the tone only when its intensity level is increased by \(7.8 \mathrm{dB}\) relative to the just-audible intensity level for the woman. What is the ratio of the sound intensity just detected by the man to the sound intensity just detected by the woman?

The speed of a transverse wave on a string is \(450 \mathrm{m} / \mathrm{s},\) and the wavelength is \(0.18 \mathrm{m}\). The amplitude of the wave is \(2.0 \mathrm{mm}\). How much time is required for a particle of the string to move through a total distance of \(1.0 \mathrm{km} ?\)

A copper wire, whose cross-sectional area is \(1.1 \times 10^{-6} \mathrm{m}^{2}\), has a linear density of \(9.8 \times 10^{-3} \mathrm{kg} / \mathrm{m}\) and is strung between two walls. At the ambient temperature, a transverse wave travels with a speed of \(46 \mathrm{m} / \mathrm{s}\) on this wire. The coefficient of linear expansion for copper is \(17 \times 10^{-6}\left(\mathrm{C}^{\circ}\right)^{-1},\) and Young's modulus for copper is \(1.1 \times 10^{11} \mathrm{N} / \mathrm{m}^{2} .\) What will be the speed of the wave when the temperature is lowered by \(14 \mathrm{C}^{\circ}\) ? Ignore any change in the linear density caused by the change in temperature.

A car is parked \(20.0 \mathrm{m}\) directly south of a railroad crossing. A train is approaching the crossing from the west, headed directly east at a speed of \(55.0 \mathrm{m} / \mathrm{s}\). The train sounds a short blast of its \(289-\mathrm{Hz}\) horn when it reaches a point \(20.0 \mathrm{m}\) west of the crossing. What frequency does the car's driver hear when the horn blast reaches the car? The speed of sound in air is \(343 \mathrm{m} / \mathrm{s}\). (Hint: Assume that only the component of the train's velocity that is directed toward the car affects the frequency heard by the driver.

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