1. THERMAL EQUILIBRIUM
DE LA SALLE SANTIAGO ZOBEL SCHOOL
HIGH SCHOOL SCIENCE DEPARTMENT
SY 2012-2013 / TERM 2
PHYSICAL SCIENCE
MODULE 2.2 – HEAT AND TEMPERATURE

2. Lesson Objectives:
Recall how heat transfer happens;
Define thermal equilibrium;
Explain how the law of conservation of energy applies to heat transfer,;
and objects in thermal equilibrium; and
Systematically solve problems on calorimetry and methods of mixtures
by applying the formula of the law of conservation of energy in
thermal systems.

3. Objects in “Thermal Contact”
If you mix cold milk with hot coffee,
Will heat transfer happen within
the milk-coffee mixture? Why?
What will be the direction of
heat flow? Why?
After some time, what do you
think will happen to the
temperature of the milk-coffee
mixture?

4. Thermal Equilibrium
the condition when objects in
thermal contact achieve a
common final temperature
in this state, no NET heat Object A Object B
transfer happens between the
two objects in thermal contact
the sum of all heat gained and
heat lost in the thermal
system is equal to zero

5. The Law of Conservation of Energy
“Energy can neither be created
nor destroyed.”
or In a thermal system, this law
applies such that no heat
(energy) is created nor
destroyed.
or
Therefore, all heat gained
should balance all heat lost in
a thermal system.

6. Objects in Thermal Equilibrium
When objects achieve the state of thermal equilibrium, the formula of
the law of conservation of energy in thermal systems can be used to solve
for the common final temperature of the system and other involved
variables.
Note that the formula
is just the same as

7. Sample Problem
A 100 oC nickel coin with a mass of 10-g is immersed in a 50-g glass of
water at 20 oC. The specific heat of nickel is 0.44 J/g oC while water’s
specific heat is 4.18 J/g oC. What is the final temperature of the system when
it achieves thermal equilibrium?