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Adding heat for final temperature

  • Thread starter shakejuhn
  • Start date
17
0
1. Homework Statement
How much heat is required to raise the temperature of 0.250kg of water from 20.0oC to 30.0oC?

If this amount of heat is added to an equal mass of mercury that is initially at 20.0oC, what is its final temperature?


2. Homework Equations

Q=c*M*(t2-t1)

3. The Attempt at a Solution

for the first part i got
q=1*0.250*(30.0-20.0)
q=10.4725
this is wrong the correct answer was 1.05*10^4
how did they get that answer?

The second part i have so far
1.05*10^4=c*0.250*(t2-20)
it didnt say what the spefice heat of mercury was so i looked it up and it was 0.140
1.05*10^4=0.140*0.250*(t2-20)
1.05*10^4/(.035)+20

please help with this
 

hage567

Homework Helper
1,509
1
For the first part why are you using 1 for c? Look up the specific heat of water. Regardless, I don't see how you got 10.4725 from your equation for q. Is there a typo in there somewhere?
 

Andrew Mason

Science Advisor
Homework Helper
7,535
315
1. Homework Statement
How much heat is required to raise the temperature of 0.250kg of water from 20.0oC to 30.0oC?

If this amount of heat is added to an equal mass of mercury that is initially at 20.0oC, what is its final temperature?


2. Homework Equations

Q=c*M*(t2-t1)

3. The Attempt at a Solution

for the first part i got
q=1*0.250*(30.0-20.0)
q=10.4725
this is wrong the correct answer was 1.05*10^4
how did they get that answer?

The second part i have so far
1.05*10^4=c*0.250*(t2-20)
it didnt say what the spefice heat of mercury was so i looked it up and it was 0.140
1.05*10^4=0.140*0.250*(t2-20)
1.05*10^4/(.035)+20

please help with this
You have to be clear on your units. You appear to be working in calories and kg. If so, you have to use a specific heat for water in calories/kg deg not calories/g deg.

AM
 
17
0
i just said find the answer in joules
 

Andrew Mason

Science Advisor
Homework Helper
7,535
315
i just said find the answer in joules
If you are using a specific heat of 1 for water you are working in calories/g. Kelvin. If you want the answer in joules you have to multiply the answer by 4.186 (ie. 4.186 J in one cal.). The specific heat for water in Joules/Kg K is 4186.

AM
 
Last edited:

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