Heat added to Monatomic Gas at Constant Pressure

  • #1

Homework Statement



If 650 J of heat are added to 21 moles of a monatomic gas at constant pressure, how much does the temperature of the gas increase? (in Kelvins)

Homework Equations


U = nRT
Q=(5/2)nR(T2-T1)


The Attempt at a Solution



well how do you even know how much the temperature changes by if they dont give u an initial temperature? or is it just as simple as solving for delta T in which you just do

650J = (5/2)(21)( 8.31 J/mol.K )(Delta T)

is it really that simple or do i have to do something with the 21 moles and convert it or anything? and once i do get the Delta T must that be converted or something in order to have it end up in Kelvins? I ended up with 1.4899K im not sure if that's right though.
 

Answers and Replies

  • #2
ehild
Homework Helper
15,543
1,909
It is correct. Do not write it out with more than 3 digits.


ehild
 
  • #3
Andrew Mason
Science Advisor
Homework Helper
7,656
383

Homework Statement



If 650 J of heat are added to 21 moles of a monatomic gas at constant pressure, how much does the temperature of the gas increase? (in Kelvins)

Homework Equations


U = nRT
Careful. For a monatomic ideal gas, internal energy, U = 3nRT/2
Q=(5/2)nR(T2-T1)
Note that T is in Kelvins, and Q is in Joules and R is in Joule/mol Kelvin. The molar heat capacity Cp (=5R/2) is temperature independent ie. it is the same for all T.

The Attempt at a Solution



well how do you even know how much the temperature changes by if they dont give u an initial temperature? or is it just as simple as solving for delta T in which you just do

650J = (5/2)(21)( 8.31 J/mol.K )(Delta T)

is it really that simple ...
It is that simple.

AM
 
  • #4
wait so is it 3/2 or 5/2? cuz i have 2 equations from the formula sheet he gave us one says

Cp = 5/2 * R and one says Cv = 3/2 * R ? or in this case is it the 3/2*5/2 or something?
 
  • #5
ehild
Homework Helper
15,543
1,909
Cp is the molar specific heat capacity at constant pressure, and it is 5/2 R for mono-atomic gases. You add heat at constant pressure, so Cp was correctly used.

ehild
 
  • #6
thank you guys, appreciate it alot
 
  • #7
Andrew Mason
Science Advisor
Homework Helper
7,656
383
wait so is it 3/2 or 5/2? cuz i have 2 equations from the formula sheet he gave us one says

Cp = 5/2 * R and one says Cv = 3/2 * R ? or in this case is it the 3/2*5/2 or something?
Cp = 5R/2 and Cv=3R/2. But you had U = nRT. That is not correct. U = nCvT = (3/2)nRT.

AM
 

Related Threads on Heat added to Monatomic Gas at Constant Pressure

Replies
2
Views
1K
Replies
2
Views
10K
Replies
8
Views
4K
  • Last Post
Replies
12
Views
3K
Replies
3
Views
5K
Replies
9
Views
16K
Replies
1
Views
1K
Replies
3
Views
2K
  • Last Post
Replies
2
Views
12K
Replies
2
Views
2K
Top