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

A gas at 100°C fills volume V₀. If the pressure is held constant, what is the volume if (a) the Celsius temperature is doubled

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Identify the initial conditions and the final condition for the temperature. Initially, the temperature is 100°C, which is equivalent to 373.15 K (since 0°C = 273.15 K). The final temperature condition is that the Celsius temperature is doubled, so it becomes 200°C, which is equivalent to 473.15 K.
Recognize that the problem states the pressure is held constant. This means you can use Charles's Law, which relates the volume and temperature of a gas at constant pressure. Charles's Law is given by \( V_1/T_1 = V_2/T_2 \), where \( V_1 \) and \( T_1 \) are the initial volume and temperature, and \( V_2 \) and \( T_2 \) are the final volume and temperature.
Substitute the known values into Charles's Law. Set \( V_1 = V_0 \) and \( T_1 = 373.15 \) K for the initial conditions. For the final conditions, set \( T_2 = 473.15 \) K. The equation becomes \( V_0 / 373.15 = V_2 / 473.15 \).
Solve the equation for \( V_2 \), the final volume. Rearrange the equation to isolate \( V_2 \) on one side: \( V_2 = V_0 \times (473.15 / 373.15) \).
This equation gives you the relationship to find the new volume \( V_2 \) in terms of the initial volume \( V_0 \) when the temperature is doubled at constant pressure.

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Key Concepts

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

Charles's Law

Charles's Law states that the volume of a gas is directly proportional to its absolute temperature (in Kelvin) when pressure is held constant. This means that if the temperature increases, the volume will also increase, and vice versa. The relationship can be expressed mathematically as V₁/T₁ = V₂/T₂, where V is volume and T is temperature in Kelvin.
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Absolute Temperature

Absolute temperature is measured on the Kelvin scale, where 0 K represents absolute zero, the point at which molecular motion ceases. To convert Celsius to Kelvin, you add 273.15. This conversion is crucial when applying gas laws, as they require temperatures to be in absolute terms to ensure accurate calculations.
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Gas Behavior Under Constant Pressure

When a gas is subjected to constant pressure, any change in temperature will result in a corresponding change in volume, as described by Charles's Law. This principle is essential for understanding how gases expand or contract in response to temperature changes, which is particularly relevant in thermodynamic processes and applications.
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