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Exothermic and Endothermic
Processes
endothermic process is
one that absorbs heat from
the surroundings
An
Heat and Work II
the
system heats up and the
surroundings cool down
Exothermic and Endothermic
Processes
Heat
flow in an
endothermic process is
defined as positive:
(+)
q
(+) ΔH
Exothermic and Endothermic
Processes
exothermic process is
one that releases heat to the
surroundings
An
the
system cools down and
the surroundings heat up
Exothermic and Endothermic
Processes
flow in an exothermic
process is defined as
negative:
Heat
(-)
q
(-) ΔH
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Energy Flow
system can exchange energy
with its surroundings in the form
of heat or work
 We express this relationship as
follows:
 ΔET = q + w
A
Energy Flow
 The
change in ET is determined
by the heat and work done by the
system:
in heat (+q/-q)
 change in work (+w/-w)
 change
Energy Flow
+
w
done by the surroundings on
the system
 work
-
w
done by the system on the
surroundings
 work
The Calorie
 The
‘calorie’ has different meanings
in common usage and in science
 Dietary
Calorie
 Thermodynamic
calorie
dietary calorie is written as
‘Cal’, using an uppercase ‘C’
 The thermodynamic calorie is written
as ‘cal’, using a lowercase ‘c’
 The
The calorie
1
Calorie = 1000 calories
 1 Cal = 1000 cal
 or
1
Cal = 1 kcal
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The calorie
 The
statement ‘10 g of sugar has
41 Calories’ means that 10 g of
sucrose releases 41 kcal of heat
energy when completely burned
 This takes place in the
combustion reactions in the
mitochondria
The calorie
thermodynamic calorie (cal) of
heat raises the temperature of 1 g of
pure, liquid water 1 OC
1
calories and Joules
The Joule
 The
SI unit of energy and heat is the
joule
 4.184 joule (J) of heat raises the
temperature of 1 g of pure, liquid
water 1 OC
 Since
1 cal represents the same
amount of heat energy as 4.184 J,
we have the following:
 1 cal = 4.184 J
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