Question

I just need quick help. When you use the formula E=mc(theta), the change in temperature is given by (final temperature-initial temperature). Right?

Answer 1

But I'm doing this question where ice is added to water at 28 degree Celsius and I'm required to calculate the final temperature of water.
However, if I use (final temperature-initial temperature) I get the wrong answer.

Answer 2

@experimentX

Answer 3

well well ... yes

Answer 4

but you forgot the latent heat of fusion.

Answer 5

I did put the latent heat of fusion as well.

Answer 6

or what do you call that ... melting!!
also note the temperature of ice ... it has different heat sp. capacity.

Answer 7

I used this equation:
Heat lost by water at 28 degree Celsius= Heat gained by ice at 0 degree Celsius + Heat absorbed by water at 0 degree Celsius

Answer 8

did change into cgs? or SI?

Answer 9

\[m1c(T-28)=l _{f} m2 + m2c(T-0)\]

Answer 10

Now if I use (28-T) in that equation, I get the right answer. Why is that so? Isn't the delta theta supposed to mean (final temp-initial temp)?

Answer 11

of course 28-T is the delta(theta)

Answer 12

the final temperature is T ... for initial temp for ice = 0
initial temp for water is 28

Answer 13

That's what I'm saying. If T is the final temp for water, then shouldn't it be (T-28)? (Final-initial)

Answer 14

delta theta for ice = T-0
delta theta for water = 28 -T

Answer 15

yes yes ... you can do that, but you have to assume that heat of the system remains constant.

Answer 16

do you get what I mean?

Answer 17

Yes, the heat remains constant. But why (28-T)? Why not (T-28) as the formula states that delta theta is the final-initial temp?

Answer 18

if you put T-28, you have to assume that heat remains constant.
change in heat of water + change in heat of ice + latent heat of fusion = constant.

Answer 19

the constant = 0
I mean the change in heat of the whole system is constant.

just consider the direction of heat flow.

Answer 20

if heat is lost then 28-T
if heat is gained, then T-28

Answer 21

The simple answer is 28 degrees minus 0 degrees equals 28 degrees as the change in temperature. The direction of change is 28 degrees cooler. As long as there is ice to melt the temperature will drop to 0 degrees. You only need to use the heat of fusion to determine how much ice needs to melt to bring the water down to 0 degrees, a different problem.