Ch 19: Work, Heat, and the First Law of Thermodynamics

Knight Calc - Physics for Scientists and Engineers 5th Edition

Knight Calc5th EditionPhysics for Scientists and EngineersISBN: 9780137344796당신이 사용하는 게 아니라요?교과서 변경

Knight Calc 5th Edition

Ch 19: Work, Heat, and the First Law of Thermodynamics

문제 75a

19장, 문제 75a

In Problems 75, 76, and 77 you are given the equation used to solve a problem. For each of these, you are to write a realistic problem for which this is the correct equation.
$50 J = - n (8.31 J/mol K) (350 K) \ln (\frac{1}{3}) (200 \times 10^{- 6} m^{3}) (13, 600 {kg/m}^{3})$

검증된 단계별 안내

Step 1: Analyze the given equation and identify the physical quantities involved. The equation includes terms such as energy (Joules), number of moles (n), gas constant (R = 8.31 J/mol·K), temperature (T = 350 K), natural logarithm (ln), volume (m³), and density (kg/m³). This suggests the problem is related to thermodynamics and possibly involves entropy or work done in a system.

Step 2: Recognize the logarithmic term ln(1/3). This indicates a ratio or change in a quantity, such as volume or pressure, which is common in processes like gas expansion or compression. The negative sign suggests a decrease in entropy or work done by the system.

Step 3: Consider the context of the equation. The presence of the gas constant and temperature implies the involvement of an ideal gas. The volume and density terms might relate to the properties of a substance undergoing a phase change or compression.

Step 4: Formulate a realistic scenario. For example, the problem could describe a gas undergoing isothermal compression where the work done is calculated using the given equation. Alternatively, it could involve a liquid being compressed, with the density and volume terms representing the properties of the liquid.

Step 5: Write the problem statement. For instance: 'A gas is compressed isothermally at a temperature of 350 K. The initial volume is 200 × 10⁻⁶ m³, and the density of the gas is 13,600 kg/m³. Calculate the work done during the compression process, given that the final volume is one-third of the initial volume.'

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주요 개념

질문에 올바르게 답하기 위해 반드시 이해해야 하는 핵심 개념들은 다음과 같습니다.

Ideal Gas Law

The Ideal Gas Law relates the pressure, volume, temperature, and number of moles of an ideal gas through the equation PV = nRT. In this context, the equation provided involves thermodynamic principles that can be applied to gases, where R is the universal gas constant. Understanding this law is crucial for formulating problems involving gas behavior under varying conditions.

Thermodynamic Processes

Thermodynamic processes describe how energy is transferred and transformed in a system. The equation given suggests a process involving heat transfer and work done, which are key components in thermodynamics. Recognizing the type of process (isothermal, adiabatic, etc.) is essential for creating realistic problems that align with the equation.

Natural Logarithm in Thermodynamics

The natural logarithm appears frequently in thermodynamic equations, particularly in calculations involving entropy and the change in state variables. In the provided equation, ln(1/3) indicates a relationship between the state of the system and its entropy change. Understanding how to manipulate logarithmic functions is vital for solving problems that involve exponential relationships in thermodynamics.

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