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13/14 Semester 2
Physical Chemistry I
(TKK-2246)
Instructor: Rama Oktavian
Email: [email protected]
Office Hr.: M.13-15, Tu. 13-15, W. 13-15, Th. 13-15, F. 09-11
Outlines
1. Review
2. Thermodynamic terms
3. Heat and work
4. 1st law of thermodynamic
Review
Gas properties
Properties of gas
Macroscopic properties
Properties that can be observed and
measured
• Properties of bulk gases
• Observable
Microscopic view of a solid
How to make relation between those
macroscopic properties of gas??
– Pressure, volume, mass, temperature..
The general form of an equation of state is
p=f(T,V,n)
Review
Gases Exert Pressure: What is Pressure?
Pressure is defined as the force exerted divided by the area it acts over
Pressure = Force/Area
The SI unit of pressure, the pascal(Pa), is
defined as 1 newton per metre-squared:
1 Pa =1 N m−2
1 Pa =1 kg m−1s−2
1 atm =1.013 25 ×105Pa exactly 1 bar =105Pa
Review
Pressure measurement
Barometer – device that measures
atmospheric pressure
Invented by Evangelista Torricelli in 1643
the height of the mercury column is
proportional to the external pressure
Review
Pressure measurement
Review
Boyle’s law
• Boyle’s Law is one of the laws in physics that concern the
behaviour of gases
• When a gas is under pressure it takes up less space:
• The higher the pressure, the smaller the volume
• Boyles Law tells us about the relationship between the volume of a
gas and its pressure at a constant temperature
• The law states that pressure is inversely proportional to the
volume
Review
Charles’s law
• French chemist Jacques Charles discovered that the volume of a gas at
constant pressure changes with temperature.
• As the temperature of the gas increases, so does its volume, and as its
temperature decreases, so does its volume.
• The law says that at constant pressure, the volume of a fixed number of
particles of gas is directly proportional to the absolute (Kelvin) temperature
Review
Avogadro’s law
Avogadro’s law states that
 the volume of a gas is
directly related to the
number of moles (n) of
gas
 T and P are constant
V1 = V2
n1
n2
Ideal Gas law
The combination of those laws gives
Usually written as:
R is gas constant
Ideal Gas law
R is known as universal gas constant
Using STP conditions
PV
R
nT
(1atm)( 22.4 L)
R
(1mol )( 273.15K )
R  0.0821(atm.L)(mol.K )
1
Equation of state
Equation of state
The general form of an equation of state is
p=f(T,V,n)
PV  nRT
Ideal gas equation is equation of state
Equation of state
Equation of state
PV  nRT
P, V, n, T are properties
Intensive properties – independent on the quantity of material
P, T
Extensive properties – dependent on the quantity of material
n, V
The ratio of any two extensive
variables is always an intensive
variable
Intensive properties
Ideal gas and Real gas
Ideal gas
pV  RT
The ideal gas law was useful in determining the properties of a specific
sample of gas at constant T, P, V, and n.
We often need to know how a change in one (or more) properties impacts the
other properties for a sample of a gas
Ideal gas and Real gas
Real gas
pV  RT
deviations from the perfect gas law because molecules interact
with one another
Repulsive forces are significant only when molecules are
almost in contact
Attractive intermolecular forces have a relatively long range and are
effective over several molecular diameters
Molar mass of ideal gas
Determination of molar mass for ideal gas
Ideal gas equation
PV  nRT
n
w
M
 w  RT   
M  
   RT
V  P  P 
Intensive properties and
measurable
Dalton’s law
Partial pressure
Dalton’s law
Kinetic theory of gases
Pressure and molecular speed relation
1
pV  nMc 2
3
(1)
Where M = mNA, the molar mass of the molecules, and c is the root mean
square speed of the molecules, the square root of the mean of the squares of the
speeds, v, of the molecules:
c v
2 12
(2)
Kinetic theory of gases
Pressure and molecular speed relation
Using Boyle’s Law and ideal gas Law
1
nRT  nMc 2
3
the root mean square speed of the molecules in a gas at a temperature T must
be
the higher the temperature, the higher the root mean square speed of the
molecules, and, at a given temperature, heavy molecules travel more slowly than
light molecules
Kinetic theory of gases
Pressure and kinetic energy relation
Kinetic energy of molecule is defined as
1 2
  mc
2
1
pV  nMc 2
3
2
pV  nN A
3
M = mNA
N = nNA
2
pV  N
3
Kinetic theory of gases
Pressure and kinetic energy relation
Using Boyle’s Law and ideal gas Law
2
nRT  N
3
3 RT

2 NA
3
  kT
2
k is Boltzmann constant
k = 1.3806488 × 10-23 m2 kg s-2 K-1
Condensed Phase
The definition of “condensed phase”
made denser, especially reduced from a gaseous to a liquid state.
Liquid properties
General definition of
1  V 
 

V  T  p
1  V 

V  P T
  

and

Volume expansivity
The value is usually small
Isothermal compressibility
Liquid properties
General definition of

and

Thermodynamic terms
What is thermodynamic?
the study of the transformations of energy
enables us to discuss all matters quantitatively and to make useful
predictions
e.g: The release of energy can be used to provide heat when a fuel
burns in a furnace, to produce mechanical work when a fuel burns in
an engine, and to generate electrical work when a chemical reaction
pumps electrons through a circuit
Thermodynamic terms
Thermodynamic terms
A thermodynamic system is that
part of the physical universe
the properties of which are under
investigation
A system is isolated when the
boundary prevents any
interaction with the surroundings
A system is called open when
mass passes across the
boundary, closed when no mass
passes the boundary
Thermodynamic terms
Thermodynamic terms
Properties of a System - physical attributes that are perceived by the senses, or
are made perceptible by certain experimental methods of investigation
1. non-measurable, as the kinds of substances composing a system and the
states of aggregation of its parts
2. measurable, as pressure and volume, to which a numerical value can be
assigned by a direct or indirect comparison with a standard
Thermodynamic terms
State of a System. A system is in a definite state when each of its properties has
a definite value.
Change in State, Path, Cycle, Process. Let a system undergo a change in its
state from a specified initial to a specified final state
The change in state is completely defined when the initial and the final states are
specified
The path of the change in state is defined by giving the initial state, the sequence
of intermediate states arranged in the order traversed by the system, and the final
state
Thermodynamic terms
A process is the method of operation by means of which a change in state is
effected
State Variable, . . . . A state variable is one that has a definite value when the
state of a system is specified . . . .
Path Variable,… Variable that do depend on path
Heat, work, and energy
Work (W) - any quantity that flows across the boundary of a system during a
change in its state
Ex:
- gas that pushes out a piston and raises a weight
- A chemical reaction that drives an electric current
through a resistance also does work
Heat, work, and energy
Heat (Q) - any quantity that flows across the boundary of a system as a result of a
temperature difference between the system and its surroundings
The internal energy (U) of a system is identified with the random, disordered
motion of molecules. The internal energy is a state function
Heat, work, and energy
Consider a system consisting of 10 g of liquid water contained in an open beaker
under constant pressure of 1 atm. Initially the water is at 25 °C
the initial state : p = 1 atm, t = 25 °C
The system is contacted with 100 g of water at a high temperature, 90 °C. The
system is kept in contact with this 100 g of water until the temperature of the 100
g has fallen to 89 °C
The final state of the system is described by p = 1 atm, t = 35 °C and heat flows
from surrounding into the system
Heat, work, and energy
Change of state due to work
Initial state : 10 g of water, p = 1 atm, t = 25 °C
Then the final state is p = 1 atm, t = 35 °C
There was no heat flow, but there was a flow of work
Heat, work, and energy
Heat and work are called path functions
1st law of thermodynamics
The internal energy of an isolated system is constant
heat and work are equivalent ways of changing a system’s internal energy.
The 1st Law of Thermodyamics simply states that energy can be neither created
nor destroyed (conservation of energy)
1st law of thermodynamics
Mathematical statement for The 1st Law of Thermodyamics
ΔU = q + w
in which w > 0 or q > 0 if energy is transferred to the system as work or heat
and w < 0 or q < 0 if energy is lost from the system as work or heat
1st law of thermodynamics
1st law of thermodynamics
Consider the combustion process that occurs in the cylinder of an automobile:
2C8H18(l) + 25O2(g)  16CO2(g) + 18H2O(g)
because the reaction produces a greater amount of gas than is consumed, the reaction
pushes the piston upward against the force of gravity and the tension of the camshaft.
The point is that this process involves some work
Define: What is the system and surroundings, the sign of heat and work