Joule Thomson Effect Lab Report

2.1 Joule Thomson effect: The phenomenon of producing lowering of temperature when a gas is made to expand adiabatically from a region of high pressure into a region of low pressure, is known as joule Thomson effect.

The experimental set up is shown in figure 2(a). it consists of a thermally insulated tube fitted with a po-rous plug and two weightless and frictionless pistons X and Y. two sensitive thermometers are fitted on both the sides of the porous plug to record temperature.

Consider that a certain amount of the gas is passed through the porous plug by slow movement of piston X, i.e. a volume V1 of the gas at pressure P1 be forced through the plug on the left side of the plug. The gas in the right hand chamber is allowed to expand

Thus, work is done on the gas. It is equal to P1V1. The work done on the right hand side by the gas is equal to P2V2. Total work done by the gas = P1V1 – P2V2

As q = 0, the work done by the gas lowers its internal energy and constantly temperature falls.

ΔE = P1V1-P2V2

E2- E1 = P1V1-P2V2 ( E2 + P2V2 ) – ( E1 + P1V1 ) = 0 or H2 – H1 = 0 or ΔH = 0

Thus, joule – Thomson effect occurs at constant enthalpy.

• Joule Thomson coefficient: - The number of degrees of temperature change produced per atmos-pheric drop in pressure under constant enthalpy conditions when the gas is allowed to expand through porous plug is called joule Thomson effect. It is denoted by µ. µ = dT / dP

Figure 2 (a)- joule Thomson effect

2.2 1ST LAW OF THERMODYNAMICS: - According to this,

The energy can neither be produced nor demolished although it may be transformed from one form to another.

• The energy or heat of an isolated system is persistent.

• The 1STlaw of thermodynamics is simply the law of conservation of

Most of the important laws of Physical Chemistry, including the vent’s Hoff law of lowering of vapour pressure, Phase Rule and the Distribution Law, can be derived from the laws of thermo-dynamics. 3.2. Limits of the first law of thermodynamics are discussed below:

1. No limitation on the way of the flow of heat: the first commandment establishes definite relationship among the heat absorbed and the work performed by a system. The first law does not specify whether energy or heat can flow from a cold end to a hot end or not. For example: we cannot abstract heat as of the ice by cooling it to a low temperature. Certain external effort has to be done.

2. Does not require the probability of the reaction: first law does not postulate that process is feasible or not for example: when a rod is heated at one end then equilibrium has to be obtained which is possible only by some expenditure of energy.

3. Basically it is not possible to change the heat energy into an equivalent amount of work.

To overcome this limits, another law is required which is recognized as second law of thermodynamics.

The second law of thermodynamics benefits us to calculate whether the reaction is feasible or not and also tell the direction of the flow of