Register to reply

Thermal physics- Can you make good tea at a certain pressure?

by H.fulls
Tags: physics, pressure, thermal
Share this thread:
H.fulls
#1
Nov20-12, 09:22 AM
P: 18
1. The problem statement, all variables and given/known data
According to experts good tea can only be made at temperatures greater than 97 degrees celsius. If this is true, can you brew good tea at elevation 4km (Pressure = 6.2*[itex]10^{4}[/itex]Pa) . Given that latent heat of vaporisation for water is 2.4*[itex]10^{6}[/itex] J/kg and water has a molar mass of 18g.


2. Relevant equations
Clausius-clapeyron equation [itex]\frac{dp}{dT}[/itex] = [itex]\frac{L}{T(V2-V1)}[/itex]
but V1 is negligable so [itex]\frac{dp}{dT}[/itex] = [itex]\frac{L}{TV2}[/itex]

Ideal gas equation pV=nRT


3. The attempt at a solution

Tried to integrate so have [itex]\int\frac{1}{p}dp[/itex]=[itex]\frac{L}{R}[/itex][itex]\int\frac{1}{T^{2}}dT[/itex]
from substituting in V = [itex]\frac{RT}{p}[/itex] from ideal gas equation.
But dont really know what to do from here! I dont know what limits to put in for the integral or if im just going about this all wrong from the start!
Ive been told the clausius-clapeyron statement must be used by my professor!
Any suggestions would be helpful! Thankyou!
Phys.Org News Partner Science news on Phys.org
Apple to unveil 'iWatch' on September 9
NASA deep-space rocket, SLS, to launch in 2018
Study examines 13,000-year-old nanodiamonds from multiple locations across three continents
JesseC
#2
Nov20-12, 03:43 PM
P: 282
I think what the question is really asking is, at what temperature does water boil at an altitude of 4km? If it boils at over 97C then the tea you make will be 'good', if not, it will be 'bad'.

Why don't you try integrating from p0 to p1 and from T0 to T1 where p0 and T0 are reference pressure and temperatures which you know. The question then becomes, what is the pressure at 4km above sea level?
haruspex
#3
Nov20-12, 07:22 PM
Homework
Sci Advisor
HW Helper
Thanks
P: 9,839
Quote Quote by JesseC View Post
The question then becomes, what is the pressure at 4km above sea level?
The pressure at 4km was given.

rude man
#4
Nov21-12, 04:31 PM
HW Helper
Thanks
PF Gold
rude man's Avatar
P: 4,842
Thermal physics- Can you make good tea at a certain pressure?

Boiling is when saturated vapor pressure = atmospheric pressure. So get a table of sat. vapor pressure vs. temperature for water and see if T corresponding to your altitude pressure is > 97C.
JesseC
#5
Nov21-12, 06:15 PM
P: 282
Quote Quote by rude man View Post
Boiling is when saturated vapor pressure = atmospheric pressure. So get a table of sat. vapor pressure vs. temperature for water and see if T corresponding to your altitude pressure is > 97C.
The question specifically requires use of the Clausius-clapeyron equation. The answer can be reached using the equation, a couple of lines of algebra and substitution of the correct values. Tables really aren't needed :/


Register to reply

Related Discussions
Thermal Physics question regarding the thermal expansion coefficients Introductory Physics Homework 1
AP Question involving Ideal Gas Law - Thermal Physics - Pressure Introductory Physics Homework 7
Very good free online thermal Physics book Science & Math Textbooks 1
Okay, make me look good again General Discussion 4
Does good increase in the world or do the laws we make, make it appear that way? General Discussion 6