The document discusses thermal equilibrium, which is achieved when two substances at different temperatures are kept together and heat continues to transfer between them until their temperatures are equalized. It provides an example of a thermometer placed on a person's forehead registering an increasing temperature over 5 minutes as it reaches equilibrium with the person's body. It then asks students to use their knowledge of thermal equilibrium to calculate how much ice is needed to cool a drink to a certain temperature.

1. THERMAL
EQUILIBRIUM
Lesson #4

2. Objectives
 Define thermal
equilibrium

3. Solve sample
problems involving
thermal equilibrium

4. Apply thermal
equilibrium in daily
life

6. Quiet now children!
So before we begin, eyes
on the board please.
Study the illustration.

7. A thermometer is placed on the
forehead of a kid with a fever.
The thermometer
reads 98 °F

8. The thermometer was not removed
until the time reached 5 minutes.
The thermometer
now reads 101 °F
101 °F

9. Why did the Easy! Because
temperature they’re not Bu..Bu..But..
change after yet in thermal I, I can’t
some time? equilibrium! understand!
Why?!

10. What!? Remember?
When two substances having
different temperatures are
introduced or kept together, heat
flows from a substance at higher
temperature to a substance at
lower temperature.

11. To make it more
correct, heat continues to
be transferred until their
temperatures are equalized.
When this stage is
achieved, only we can say
that we can say that the
substances are in thermal
equilibrium.

12. Oohh.. So that explains why the liquid
inside the thermometer rises as time
passes by.
Yes! That is why we need to
wait for a few minutes before
taking the reading of the
thermometer.

13. Of course. With that, the kid’s
body and the thermometer will
reach the same temperature
Hey! You keep on finishing
my sentences! Why are you
late anyway?
So what? I already
understand the lesson.

14. You… you!!!!! Darn!
You’ll pay for this!!!
You’ll see! One day, I Whatever.
will beat you!! Timmy.
Holy!! My water is
now getting warmer!
Help me Timmy!!!

15. Don’t worry doggy, we’ll get
Really?
you some ice for you later
Thanks
But I
wonder how
many ice
will make
the juice
cold again?

17. Timmy needs help…
But it seems that you lost your
magic powers..
..and equipped only with the knowledge
of thermal equilibrium.
How are you going to help him?

18. First you need to Ti = 15 °C
consider the condition m = 200 g
of Doggy’s drink.
How much ice would
be enough to cool
down the temperature
of the water? (mass)
Tf = 10 °C

19. The mixture of ice and water would
eventually reach thermal equilibrium.
However, they must be in a closed
system so that heat will completely
transfer from one body to another.

20. Or simply, it must follow the Law of
Conservation of Energy
ΔE = 0
No heat will flow out of the system

21. Q+Q=0
Qlost + Qgained = 0
Qgained = - Qlost
negative denotes (where Q = mcΔT)
heat released

22. Do you now have what it takes?
Can you solve the problem of
Timmy?
Or do you wish to give up?
Well then, let us see if you can use your
skills in problem solving.

23. Ti = 15 °C
MIXED Ti = 0 °C
m = 200 g
m=?
Tf = 10 °C

24. Qgained = - Qlost
mcΔT = - (mcΔT)
mici(Tf-Tii) = - [mwcw(Tf-Tiw)]
“i” subscript for ice “w” subscript for
water

25. A 200 g sample of water
at 353 K is mixed with
200 g of water at 283 K.
What is the final
temperature of the
mixture?

26. Test Yourself

27. 3. A 100-g Aluminum
block at 373 K is placed
in 100 g of 281 K water.
The final temperature of
the liquid is 298 K. What
is the specific heat of
aluminum?