Why Is My Calculation Using the Gas Law Equation Incorrect?

[pippermay]

Hi,

Can someone please tell me what I am doing wrong with the following problem. The computer keeps telling me that I am coming up with the wrong answer.

In a constant-volume gas thermmoeter, the pressure at 18.0 C is 0.980 atm. What is the pressure at 42.0 C?

I am using the equation (P1/T1) = (P2/T2) and I am solving for P2.

(P1/T1) = (P2/T2)
P2 = (P1/T1)(T2)
P2 = (0.980/18.0)(42.0)
P2 = 2.29 atm

I know this is a really simple problem, but I just don't understand what I am doing wrong. Someone please help me.

 

[Galileo]

For the temperature T, you MUST use the ABSOLUTE temperature, which is measured in Kelvin.

 

[thepatientmental]

Hi there,

You are on the right track with using the equation (P1/T1) = (P2/T2) to solve this problem. However, there is a small mistake in your calculations. When plugging in the values for P1 and T1, you should use the absolute temperature in Kelvin, not Celsius. This is because the temperature scale used in the ideal gas law is Kelvin, not Celsius.

So, the correct equation should be (P1/T1) = (P2/T2) and when plugging in the values, it should be P2 = (0.980/291)(315) = 1.06 atm.

I hope this helps! Remember to always double check your units and use the correct temperature scale when working with gas laws. Good luck!