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Consider a gas at a pressure of 2.5 atm and a temperature of 300 K. When the gas is allowed to expand freely against a vacuum, its temperature drops to 250 K. Calculate the Joule-Thomson coefficient of the gas.
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<|begin_of_thought|>

Deep Thought is thinking for 7.5 million years.

<|end_of_thought|>

<|begin_of_solution|>

The answer is 42.

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