Pressure and Temperature -- Quick Concept Check


by forestmine
Tags: check, concept, pressure, temperature
forestmine
forestmine is offline
#1
Feb7-12, 11:34 AM
P: 182
1. The problem statement, all variables and given/known data

A fixed amount of ideal gas is held in a rigid container that expands negligibly when heated. At 20C the gas pressure is p. If we add enough heat to increase the temperature from 20C to 40C, the pressure will be less than 2p.

2. Relevant equations

pV=nRT

p_1/T_1=p_2/T_2

3. The attempt at a solution

Initially I thought the solution was simple. Solving for p_2, we have (p_1*T_2)/T_1. Plugging in 40 for T_2, and 20 for T_1 gives us 2p. Because volume, number of moles, and R are all constant, I thought it just came down to the relation between pressure and temperature, but it turns out the pressure is less than 2p, which I do not understand. Just looking for some clarification....

Thank you!
Phys.Org News Partner Science news on Phys.org
Going nuts? Turkey looks to pistachios to heat new eco-city
Space-tested fluid flow concept advances infectious disease diagnoses
SpaceX launches supplies to space station (Update)
jedishrfu
jedishrfu is offline
#2
Feb7-12, 11:42 AM
P: 2,477
shouldnt T be in Kelvins ie absolute temperature?
forestmine
forestmine is offline
#3
Feb7-12, 11:55 AM
P: 182
You're right, but I guess I was thinking since 1 celsius degree is equivalent to 1 kelvin, that it shouldn't matter. Essentially, I was thinking if volume is constant, then doubling the temperature should double the pressure, no?

Or does is it significant that we use kelvins, in which case it does turn out to be less than 2p?

smize
smize is offline
#4
Feb7-12, 12:08 PM
P: 78

Pressure and Temperature -- Quick Concept Check


Mathematically, think of Celsius as (kelvin -273)
if you double Celsius, you get (2k - 546) so essentially you double both the difference between Kelvin and Celsius as well as the change in kelvin. You ALWAYS should use Kelvin, It helps.
forestmine
forestmine is offline
#5
Feb7-12, 12:12 PM
P: 182
Ok, should have caught that. Thanks guys.


Register to reply

Related Discussions
Integration concept check Calculus & Beyond Homework 1
Concept Check for two Green Theorems Problems Calculus & Beyond Homework 2
True or False? Concept check! Calculus & Beyond Homework 1
Vector spaces - concept check Calculus & Beyond Homework 6
Max/Min power Transfer In String concept check Introductory Physics Homework 0