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Ch 18: A Macroscopic Description of Matter
Chapter 18, Problem 18

A gas with initial state variables p₁, V₁ , and T₁ expands isothermally until V₂=2V₁. What are and (b) p₂?

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Identify the initial conditions and the final condition of the gas. The initial conditions are given as p₁ (initial pressure), V₁ (initial volume), and T₁ (initial temperature). The final condition is that the volume doubles, V₂ = 2V₁.
Recognize that the process is isothermal, meaning the temperature remains constant throughout the process (T₂ = T₁).
Use the ideal gas law, which states PV = nRT, where P is the pressure, V is the volume, n is the number of moles of the gas, R is the ideal gas constant, and T is the temperature. Since the temperature is constant and assuming the amount of gas (n) does not change, the product PV remains constant.
Set up the equation for the initial and final states using the ideal gas law. Since PV is constant, p₁V₁ = p₂V₂.
Substitute V₂ = 2V₁ into the equation and solve for p₂. The equation becomes p₁V₁ = p₂(2V₁). Simplify this to find p₂ in terms of p₁.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Isothermal Process

An isothermal process occurs at a constant temperature, meaning that the internal energy of an ideal gas remains unchanged during the expansion or compression. In this scenario, as the gas expands, it absorbs heat from its surroundings to maintain the temperature, which is crucial for applying the ideal gas law.
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Ideal Gas Law

The ideal gas law is a fundamental equation in thermodynamics, expressed as PV = nRT, where P is pressure, V is volume, n is the number of moles, R is the ideal gas constant, and T is temperature. This law allows us to relate the state variables of a gas and is essential for calculating the final pressure after the gas expands isothermally.
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Boyle's Law

Boyle's Law states that for a given mass of gas at constant temperature, the product of pressure and volume is constant (P₁V₁ = P₂V₂). In the context of the isothermal expansion described, this law helps us determine the final pressure (p₂) after the gas volume doubles, as it directly relates the initial and final states of the gas.
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