Thermodynamics
The study of energy and itrs transformations
Thermochemistry
The relationships between chemical reactions and energy changes
Electrostatic Potential
arises from the interactions between charged particles
Eel = k(Q1xQ2)/d
k = 8.99x10^9 J-m/C^2
the charges of Q1 and Q2 ar...
the relationships between chemical reactions and e
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Chemistry 101 - Chapter 5
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Chemistry 101 - Chapter 5 GRADE A+
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Thermodynamics
The study of energy and itrs transformations
Thermochemistry
The relationships between chemical reactions and energy changes
Electrostatic Potential
arises from the interactions between charged particles
Eel = k(Q1xQ2)/d
k = 8.99x10^9 J-m/C^2
the charges of Q1 and Q2 are typically on the order of magnitude of
the charge of an electron (1.60x10^-19 C)
When Q1 and Q2 are of the same charge, they will repel, making Eel a
positive number
When Q1 and Q2 are opposite charges, they will attract, and Eel will
be negative
A positively charged particle and a negatively charged particle are
initially far apart. What happens to their electrostatic potential
energy as they are brought closer together?
As the distance decreases, the overall Eel will get more negative
Fundamental principle of Thermochemistry
Energy is released when chemical bonds are formed;energy is consumed when
chemical bonds are broken.
If the ions in the picture were allowed to move freely, they would
______________ and the potential energy of the system would
_____________
(check image)
a) attract
b) decrease
,This is because, as long as the ions are not too far apart, they will
fight to come together (highest point of potential energy); therefore
as they do get closer, the potential energy decreases
The First Law of Thermodynamics
Energy can be converted, but never created nor destroyed
Energy is conserved in any process; one way to express teh law is
that the change in internal energy, DeltaE, of a system in any
process is equal to the heat, q, added to the system, plus work, w,
done on the system
Delta E = q + w
System
the portion of the universe that we single out for study; A chemical
reaction is an example of a system
Surroundings
everything that lies outside the system that we study; spectator ions
or the container for the chemical reaction are examples of
surroundings
Anything that does not affect the chemical reaction
Open System
a system in which matter and energy can be exchanged with the
surroundings
ex: uncovered pot of boiling water
Closed system
systems that can exchange energy but not matter with their
surroundings
ex: mixture of H2 gas and O2 gas in a cylinder fitted with a piston
Isolated System
a system in which neither energy nor matter can be exchanged with the
surroundings
ex: insulated thermos containing hot coffee
Is a human being an isolated, closed, or open system?
Open because we exchange matter and energy with our surroundings
Internal Energy
E
The sum of ALL kinetic and potential energies of the components of the system
, The change of internal energy (Delta E) is defined as the heat, added to the system,
plus the work, done on the system by its surroundings
ΔE = q + w
ΔE = E final - E initial
Change in energy and what does it mean?
Thermodynamic quantities such as ΔE have three parts:
1) a number
2) a unit
3) a sign
(1) and (2) together give the magnitude of the change, (3) gives the direction
Apositive value of ΔE results when E final > E initial, indicating that the system has
gained energy from its surroundings.
A negative value of ΔE results when E final < E initial, indicating that the system has
lost energy to its surroundings
Note = there is an inverse relation to how much energy is in the surroundings
compared to the system. If the internal energy increases, then the surroundings
decrease. If the internal energy of the system decreases then the surroundings increase.
What is the value of ΔE if Efinal equals Einitial?
ΔE will be 0
Suppose a system receives a “deposit” of 50 J of work from the surroundings and
loses a “withdrawal” of 85 J of heat to the surroundings. What is the magnitude and
the sign of ΔE for this process?
ΔE = q + w
= 50 - 85
= -35 J
Gases A(g) and B(g) are confined in a cylinder-and-piston arrangement like that in
Figure 5.4 and react to form a solid product C(s): A (g) + B (g) ---> C (s). As the
reaction occurs, the system loses 1150 J of heat to the surroundings. The piston moves
downward as the gases react to form a solid. As the volume of the gas decreases under
the constant pressure of the atmosphere, the surroundings do 480 J of work on the
system. What is the change in the internal energy of the system?
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