Delta T in Calorimetry always positive?

RaulTheUCSCSlug

Gold Member
179
25
upload_2015-10-22_15-5-34.png


For part number 5, it says to make sure that each ΔT is positive. Why is this? Couldn't it be a negative? Or does it have to be positive since if it wasn't you would be getting heat going in the wrong direction? Like the one substance would be gaining instead of losing the heat? Which would violate the second law of thermodynamics, since entropy cannot be lowered?
 

jtbell

Mentor
15,369
3,115
For part number 5, it says to make sure that each ΔT is positive. Why is this?
First, in step 2 they've written conservation of energy as "heat gained = heat lost".
Second, in step 3, Q(gain) and Q(lost) are defined so that the difference in temperature is always positive.

An alternative method would be to write conservation of energy as something like "total heat = 0", then define both Q(gain) and Q(lost) as mc(Tf - Ti). This would make a Q(gain) positive and a Q(lost) negative.

Your book's method basically moves all the Q(lost)'s over to the other side of the equation and changes their sign to make them positive.
 

Related Threads for: Delta T in Calorimetry always positive?

Replies
2
Views
2K
Replies
1
Views
896
Replies
5
Views
2K
  • Posted
Replies
16
Views
20K
Replies
1
Views
3K
Replies
4
Views
8K
Replies
4
Views
2K

Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving

Hot Threads

Top