In an automobile engine, the piston compresses a mixture of gasoline vapor and air before ignition occurs. The combined gas law can be used to calculate the new pressure. Assume that, when the piston is pushed in, the volume inside the chamber is decreased from 100. cm³ to 20. cm³ before ignition. Suppose that the compression is isothermal; estimate the final pressure of the compressed gas mixture, given an initial pressure of 1.00 atm.

ANTICIPATE The volume is reduced by a factor of 5 at constant temperature, so you should expect a fivefold increase in pressure.

PLAN Use the combined gas law, Eq. 5. Only the pressure and volume change, so all other variables cancel, resulting in Boyle’s law.

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