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
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