If you were designing an air-conditioning system in which a cooling effect is achieved by the expansion of a gas, you might need to assess the pressure changes of the gas as it underwent changes in both temperature and volume. A sample of gas of volume 500. mL at 28.0°C was found to exert a pressure of 92.0 kPa. What pressure will the sample exert when it is compressed to 300. mL and cooled to 25.0°C?

ANTICIPATE Your problem is to judge whether the compression, which will increase the pressure, dominates the cooling, which will decrease the pressure. On the Kelvin scale, the change in temperature is quite small, so you should expect compression to dominate.

PLAN Use the combined gas law, Eq. 5, noting that only the amount is the same in the two states.

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initial final conditions conditions P₁V₁ n, T₁ = P₂V₂ n₂T₂ (5)