-Properties of Pure Substances -first law of thermodynamics and applications

-Definition of Pure Substance A pure substance has a homogeneous and invariable chemical composition and may exist in more than one phase. -Phases of Pure Substance Solid Liquid Gas

Phase Change Process of Pure Substance

T=constant vapor solid p Triple line Solid+Vapor T Critical point 1” 2” 3” 4” 5” c c 1’ 2’ 3’ 4’ 5’ 5 5” 1” 2” 3” 4” 5’ 1’ 2’ 3’ 4’ 1 2 3 4 1 2 3 4 5 vapor Liquid +Vapor Critical point Liquid Liquid +solid Solid+Vapor solid p T Triple line

P-V-T Surface - Critical point - Triple point (line)

Extract on freezing Melting line Expand on freezing P liquid Critical point P liquid Vaporization Solid Vapor Sublimation T

Property In addition to the temperature, pressure, and volume data, contain the data for the specific internal energy u the specific enthalpy h and the specific entropy s. The enthalpy is a convenient grouping of the internal energy, pressure, and volume and is given by The enthalpy per unit mass is

Solid i, Liquid f, Vapour g

First law of thermodynamics -Energy can be changed from one form to another, but it cannot be created or destroyed. The total amount of energy and matter in the Universe remains constant, merely changing from one form to another.

Wb,out Wa,in Qa,out Qb,in W is net work done by the system Q is net heat

If the work is done by the system on the surroundings, e. g If the work is done by the system on the surroundings, e.g., when a fluid expands pushing a piston outwards, the work is said to be positive. i.e., Work output of the system = + W If the work is done on the system by the surroundings, e.g., when a force is applied to a rotating handle, or to a piston to compress a fluid, the work is said to be negative. i.e., Work input to system = – W Heat received by the system = + Q Heat rejected or given up by the system = – Q.

If properties of system do not change in time Or Cycle is a process at the end of which system returns to an original state. Refrigeration/Heat-pump cycle Power plant cycle

2-5 The Ideal-Gas Equation of State The molecules of ideal-gas have no volume There are no attraction among molecules of ideal-gas 2-5-2 The Ideal-Gas Equation of State (1). pV = mRT pv=RT R------The gas constant (2) pVm = μRμT pvm=RμT Rμ-----The universal gas constant = 8.314kJ/kmol.K

The First Law of Thermodynamics The First Law of Thermodynamics. Application to a particular case: A gas confined in a cylinder with a movable piston Work done on the system, Won , is the energy transferred as work to the system. When this energy is added to the system its value will be positive. The work done on the gas in an expansion is P- V diagrams Constant pressure If 5 L of an ideal gas at a pressure of 2 atm is cooled so that it contracts at constant pressure until its volume is 3 L what is the work done on the gas? [405.2 J]

P- V diagrams Isothermal The First Law of Thermodynamics. P-V diagrams P- V diagrams Isothermal Conecting an initial state and a final state by three paths Constant pressure Constant Volume Constant Temperature

Adiabatic Processes. No heat flows into or out of the system The First Law of Thermodynamics. Processes. P-V Diagrams Adiabatic Processes. No heat flows into or out of the system

Adiabatic Processes. No heat flows into or out of the system The First Law of Thermodynamics. Processes. P-V Diagrams Adiabatic Processes. No heat flows into or out of the system The equation of curve describing the adiabatic process is We can use the ideal gas to rewrite the work done on the gas in an adiabatic process in the form A quantity of air is compressed adiabatically and quasi-statically from an initial pressure of 1 atm and a volume of 4 L at temperature of 20ºC to half its original volume. Find (a) the final pressure, (b) the final temperature and (c) the work done on the gas. cP = 29.19 J/(mol•K); cV = 20.85 J/(mol•K). M=28.84 g

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