Question

Option 2:Anna Marie is working a problem that reads “The pressure in a bicycle tire is at 105 psi at 25*C in Fresno. You take the bicycle up to Huntington, where the temperature is -5*C. What is the pressure in the tire? You can assume that volume and the number of particles is constant. Anna Marie’s solution looks like this: 105 psi (-5*C/25*C) = -21 psi. She feels pretty confident she has set up the problem correctly. You disagree with her answer. What don’t you like about her answer? How would you change about her solution? Why do you want to make that change?

Answer 1

Pressure in a bicycle tire can never be negative. Pressure always has to be greater than 0. In the solution, the temperature is taken in the units of Celsius. The temperature should be taken in absolute temperature scale i.e. Kelvin scale. The gas laws are made according to the Kelvin scale, therefore we should take temperature in Kelvin and not Celsius. Thus the answer would be:

105psi x [(-5+273)K/(25+273)K] = 94.43 psi [ Since 0 celsius corresponds to 273K, y Celsius corresponds to (y + 273)K]