Transcript
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3.1 Types of Energy
3.2 Thermodynamics
3.3Energy Changes in
Chemical Reactions
3.4 Measuring EnergyChanges: Calorimetry
3.5 Enthalpy (H)
Thermochemistry
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3.1 Types of EnergyLearning Objective
Recognize the types of energy of interest to chemists.
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The Types of Energy
Energy the ability to do work
Energy
KineticEnergy
PotentialEnergy
Electrical
Chemical
Mass
ThermalEnergy
RadiantEnergy
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Kinetic Energy
Kinetic Energy
Energy due to motion
Energy associated with randommolecularmotion, thermal energy
All moving objects have kinetic energy,dependent on velocity (v) and mass (m)
Joule (J): the SI energy unit
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Potential Energy
Potential Energy Energy due to condition, position or
composition
Energy associated with forces ofattraction orrepulsion betweenobjects
Three Types:
Electrical Energy Chemical Energy Mass
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Potential Energy
1) Electrical Energy Energy from positive andnegative ions held a small distance apart.
q1 and q2 are the charges of two ions
r is the distance between the ions in pm.
(k = 2.31 x 10-16 J pm)
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Potential Energy
2) Chemical Energy Energyresulting from attraction of theelectrons and nuclei in molecules
(bond energy)
3) Mass: Transformation of mass
into energy
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Thermal Energy the total energy of random
movements of molecules energy as a result of
electromagnetic radiation.
Thermal & Radiant Energy
Radiant Energy
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Energy Transfer &
Transformations Energy can be transferred
from one type to another.
Energy transformationsaccompany chemicalreactions.
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3.2 ThermodynamicsLearning Objective
Understand the first law of thermodynamics and the conceptsof heat and work.
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Thermodynamics
Key terms:System
Surroundings
Boundary
The study of energy transfers and transformations
how much energy goes where?
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Three Systems
Open
System
Closed
System
Isolated
System
Energy
&
Matter
Exchanged
Energy
Exchanged
No Matter
Exchanged
No
Energy
&
Matter
Exchanged
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1st Law of Thermodynamics
The Law of Conservation of Energy Energy can neither be created nor destroyed
Energy can be converted fromone form to another.
Energy of the universe is constant
The 1st
Law of Thermodynamics Application of the conversation of energy Energy may be transferred as work or heat, but no
energy can be lost, nor can heat or work beobtained from nothing
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Transfer of Energy
Two Ways! Heat Energy transferred due to a temperature
difference. Energy, as heat, flows from warm to
cool.
Work Transfer of energy by the action of a force
through a distance.
Temperature reflects the random motion ofparticles and related to kinetic energy
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Heat
Thermal energy that is exchanged with its surroundingsis referred to as heat (q) and is measured injoules (J).
Some heat flows can be determined from
temperature changes:
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Heat Flows and Temperature
1. T depends on q, the amount of heat
transferred.
2. T depends on the direction of heat flow:
If a substance absorbs heat, T > 0
If a substance releases heat, T < 0
3. T depends inversely on the amount of
material.
4. T depends on the identity of the material.
Molar heat capacity (C) amount of heat needed
to raise the temperature of 1 mol of substance by1 C.
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Temperature Change
Where
q is the amount of heat transferred
n is the number of moles of material C is the molar heat capacity of the substance
(C has units of J mol1 C1)
S
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Se can also say that
Energy transfer is directional, so we must keep track ofthe signs associated with heat flows
Reminder:
T = final temperature initial temperatureRemember to use the correct algebraic sign!
(If Tf< Ti, then the T should be negative)
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An iron kettle weighing 1.35 kg contains 2.75 kg of water at 23 C. Thekettle and water are heated to 95.0 C. How many joules of energy areabsorbed by the water and by the kettle?
( ;
)
Example 1
W k
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Work
Work (w): energy used to move an object against anopposing force
Work is a product of force (F) and displacement (d):
The amount of work depends on the magnitude of theforce
Work done by a gas: Pressure-Volume Work
Work involved in the expansion or compression of gases
W k i Ch i l P
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Work in a Chemical Process
Consider a gas confined to a cylinder with a moveablepiston of area A.
W k i Ch i l P
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Work in a Chemical Process
The external pressure is force per unit area
When the gas expands it pushes against the piston
and the piston moves a distance
h
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Work in Gases
Expansion
Work done by the gas Vf> Vi, therefore V > 0
w < 0
Esystem decreases
Compression Work done on the gas
Vf< Vi, therefore V < 0
w > 0 Esystem increases
E l 3
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A gas is allowed to expand from a volume of 2.3 L to a volume of 5.8 L.During the process, 460 J of heat is transferred from the surroundings tothe gas. (1.00 L atm = 101.325 J)
a) How much work has been done if the gas expands against a
vacuum?b) How much work has been done if the gas expands against a pressure
of 1.3 atm?
Example 3
E l 2
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Breathing requires work, even if you are unaware of it. The lung volumeof a 70 kg man at rest changed from 2.20 L to 2.70 L when he inhaled,while his lungs maintained a pressure of approximately 1.0 atm.
How much work, in liter-atmospheres and joules, was required to take a
single breath? (1.00 L atm = 101.325 J)During exercise, his lung volume changed from 2.20 L to 5.20 L on eachin-breath. How much additional work, in joules, did he require to take a
breath while exercising?
Example 2
First Law of Thermodynamics
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First Law of Thermodynamics
Simply a restatement of the law of conservation ofenergy
Internal energy (E) The sum of the potential andkinetic energies of all the particles in the system!
A change in the internal energy of a system is due tothe energy transfer, the result of a flow of work (w)
and/or heat (q).
State & Path Functions
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State & Path Functions
State Function A property of the system thatdepends only on its present state, and not how it gotthere. It is independent of pathway.
Path Function properties that depend on how thechange occurs. Distance travelled is a path function.
In thermodynamics
Work (w) and heat (q) are path dependent functions.
How much work is done and how much heat is transferreddoes depend on the pathway taken.
Distance Travelled is a Path Function
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Distance Travelled is a Path Function
Thermodynamic Path Functions
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Thermodynamic Path Functions
Energy is a state function, but heat and workare path functions
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