Chapter Seventeen
Page 504
Assess prior knowledge…
 What does a thermometer measure?
 Does a thermometer measure heat?
Energy Transformations
 Energy is the capacity for doing work or supplying
heat.
 Energy is not matter – it is detected because of its
effects
 Thermochemistry is the study of energy changes that
occur during chemical changes or changes in state.
 All matter has a certain amount of energy stored
within it.
 This is referred to as chemical potential energy.
 It is based on the substance's atomic structure.
Energy Transformations (cont'd)
 Can you think of substances we purchase that house
significant chemical potential energy?
 Energy changes occur as work, heat or a combination
of both.
 Heat (q), is energy that transfers from one object to the
next because of temperature differences between the
two.
 Adding heat causes a rise in the temperature (no
kidding).
Heat
 HEAT ALWAYS FLOWS FROM A WARMER OBJECT
TO A COOLER OBJECT.
 THE BOLD BLACK LETTERS MEANS THE
STATEMENT IS REALLY, REALLY IMPORTANT.
 Does the heat transfer continue indefinitely?
Heat Transfer
 When it comes to heat transfer, the terms system and
surroundings are often used
 The system is the object or part of the universe you focus
your attention on
 The surroundings is everything else (when it comes to
heat transfer, it is typically the 'immediate
surroundings').
 Thermochemistry is concerned with the heat flow
between the system and its surroundings.

If we rely on the law of conservation of energy, when the
system loses energy, the surroundings must gain energy and
vice versa.
Endothermic Processes
 The system absorbs heat and the surroundings cool
down.
 The heat is defined as positive (+q).
 To help you remember, endo- means "within".
Exothermic Processes
 The system releases heat and the surroundings warm
up.
 The heat is defined as negative (-q).
 The prefix exo- means "outside of"
Page 507, Q. 1 - 2
Units for Measuring Heat Flow
 Heat flow is measured in two common units, the
calorie (cal) and the joule (J).
 The joule is the SI unit for energy.
 One joule of heat raises the temperature of 1g of water
0.2390°C
 1 J = 0.2390 cal
4.184 J = 1 cal
Heat Capacity and Specific Heat
 The amount of heat needed to raise the temperature of
an object by 1°C is called its heat capacity.
 It depends on its mass and chemical composition.
 The greater the mass, the greater its heat capacity.
 Why does the parking lot at Walmart heat up faster
than a swimming pool?
 Specific heat is merely an extension of heat capacity
 It is the amount of heat it required for 1g of substance to
raise its temperature by 1°C.
Table 17.1, page 508
To calculate specific heat (C):
heat (joules or calories)
mass (g) x change in temperature (°C)
the units of specific heat are then…
J/g·°C
or
cal/g·°C
Questions 3-4, 9-11, pg. 510