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Thermal Energy
All matter is made of small particles in
constant motion
 The speed of particle motion increases
with the addition of thermal energy
 Thermal Energy – the sum of the kinetic
and potential energy of all of the atoms
in an object

Thermal Energy
 Thermal
energy increases as temperature
increases (q)
 Temperature – is the measure of the
average kinetic energy of an object’s
atoms or molecules
 Absolute Zero (-273oC) All molecular
motion stops
Temperature
 Units
of temperature include
Fahrenheit(F), Centigrade or
Celsius (C), and Kelvin (K)
 F = (1.8) C0 + 32
 K = C0 + 273
Heat
 Thermal
energy that flows from
something at a higher temperature
to something at a lower
temperature is called heat
 Thermal energy only flows from hot
to cold.
Measuring Heat
1
calorie (cal) The ability to heat 1
o
g of water 1 C
 1 Calorie = 1,000 calories also
called a kilocalorie or kcal
 1000 cal = 4180J
or
 1 cal = 4.18 J
Specific Heat
 Specific
heat is the amount of
energy needed to raise the
temperature of a material by
o
1 C or K
 Designated by Cp
Units for Measuring Heat
The Joule is the SI system unit for measuring
heat:
2
1 kg  m
1 Joule 1 newton  meter 
2
s
The calorie is the heat required to raise the
temperature of 1 gram of water by 1 Celsius
degree
1calorie  4.18 Joules
Energy
Energy is the capacity to do work, and can take
many forms
 Potential energy is stored energy or the energy
of position
 Kinetic energy is the energy of motion
 Thermal energy (heat) is an outward
manifestation of movement at the atomic level
Heat (Enthalpy) Change, ΔH
Definition: The amount of heat energy released or
absorbed during a process.
Calorimetry
The amount of heat absorbed or released during a physical
or chemical change can be measured, usually by the
change in temperature of a known quantity of water in a
calorimeter.
Exothermic Processes
Processes in which energy is released as it proceeds, and
surroundings become warmer
Reactants  Products + energy
Endothermic Processes
Processes in which energy is absorbed as it proceeds,
and surroundings become colder
Reactants + energy  Products
SPECIFIC HEAT OF WATER
 4.184
Joules per grams degree
0
Centigrade (J/g C)
Q=(m)(Cp)∆T
Q
= Specific Heat
 m = mass
 Cp = Specific Heat Capacity at
Constant Pressure
 ∆T = Change in Temperature
Calorimetry
in enthalpy = H
 q = H These terms will be used
interchangeably in this textbook
 Thus, q = H = m x C x T
 H is negative for an exothermic
reaction
 H is positive for an endothermic
reaction
 Changes
Changes in Thermal Energy
 When
heat flows into an object and
it’s temp rises the change is positive
 When heat flows out, its temp
decreases and the change is
negative
Chemistry Happens in
MOLES
 An
equation that includes energy is called
a thermochemical equation
 CH4 + 2O2  CO2 + 2H2O + 802.2 kJ
 1 mole of CH4 releases 802.2 kJ of
energy.
 When you make 802.2 kJ you also make
2 moles of water
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Thermochemical Equations
A
heat of reaction is the heat
change for the equation, exactly as
written
 The physical state of reactants and
products must also be given.
 Standard conditions for the reaction
is 101.3 kPa (1 atm.) and 25 oC
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CH4 + 2 O2  CO2 + 2 H2O + 802.2 kJ

If 10. 3 grams of CH4 are burned completely,
how much heat will be produced?
10. 3 g CH4
1 mol CH4
16.05 g CH4
802.2 kJ
1 mol CH4
= 514 kJ
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CH4 + 2 O2  CO2 + 2 H2O + 802.2 kJ
 How
many liters of O2 at STP would be
required to produce 23 kJ of heat?
 How many grams of water would be
produced with 506 kJ of heat?
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Heat of Combustion
 The
heat from the reaction that
completely burns 1 mole of a
substance
Heat of Fusion
Molar Heat of Fusion (Hfus) - the
heat absorbed by one mole of a
substance in melting from a solid to a
liquid
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Heat of Vaporization
 the
heat required to change one mole
of a substance from a liquid to a gas
when a substance vaporizes,
energy is needed.
• when a substance condenses,
energy is released.
•
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