Physical Chemistry I (TKK-2246)
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Transcript of Physical Chemistry I (TKK-2246)
Physical Chemistry I(TKK-2246)
13/14 Semester 2
Instructor: Rama OktavianEmail: [email protected] 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
ReviewGas properties
Properties of gas
Microscopic view of a solid
Properties that can be observed and
measured
Macroscopic properties
• Properties of bulk gases
• Observable
– Pressure, volume, mass, temperature..
How to make relation between those
macroscopic properties of gas??
The general form of an equation of state isp=f(T,V,n)
ReviewGases 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
ReviewPressure 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
ReviewPressure measurement
ReviewBoyle’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
ReviewCharles’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
ReviewAvogadro’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 lawR is known as universal gas constant
Using STP conditions
nTPVR
)15.273)(1()4.22)(1(KmolLatmR
1).)(.(0821.0 KmolLatmR
Equation of stateEquation of state
The general form of an equation of state is
p=f(T,V,n)
nRTPV
Ideal gas equation is equation of state
Equation of stateEquation of state
nRTPV 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
Intensive properties
The ratio of any two extensive variables is always an intensive variable
Ideal gas and Real gasIdeal gas
RTVp
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 gasReal gas
RTVp 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 gasDetermination of molar mass for ideal gas
Ideal gas equation
nRTPV
Mwn
RTPP
RTVwM
Intensive properties and measurable
Dalton’s lawPartial pressure
Dalton’s law
Kinetic theory of gasesPressure and molecular speed relation
2
31 nMcpV (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:
212vc (2)
Kinetic theory of gasesPressure and molecular speed relation
2
31 nMcnRT
Using Boyle’s Law and ideal gas Law
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 gasesPressure and kinetic energy relation
2
21 mc
Kinetic energy of molecule is defined as
2
31 nMcpV M = mNA
AnNpV32
N = nNA
NpV32
Kinetic theory of gasesPressure and kinetic energy relation
NnRT32
Using Boyle’s Law and ideal gas Law
ANRT
23
kT23
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 and
pTV
V
1 Volume expansivity
TPV
V
1 Isothermal compressibility
The value is usually small
Liquid properties
General definition of and
Thermodynamic termsWhat 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 termsThermodynamic terms
A thermodynamic system is that part of the physical universethe properties of which are under investigationA system is isolated when the boundary prevents any interaction with the surroundingsA system is called open when mass passes across the boundary, closed when no mass passes the boundary
Thermodynamic termsThermodynamic 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 currentthrough 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 °Cthe 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 °CThen the final state is p = 1 atm, t = 35 °CThere 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 thermodynamicsThe 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 thermodynamicsMathematical 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 thermodynamicsConsider 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