Epsom Salt

General Information

Magnesium sulphate heptahydrate is commonly known as Epsom Salt. The molecular formula of Epsom Salt isMgSO₄. 7H₂O. Epsom salt, named for a bitter saline spring at Epsom in Surrey, England, is not actually salt but a naturally occurring pure mineral compound of magnesium and sulfate. It is often called heptahydrate epsomite or soaking salt.

It is white in colour, salty in odour,, efflorescent crystalline substance.Crystalline Epsom loses water on heating forming anhydrous magnesium sulphate.

Occurrence

Magnesium sulphate occurs in nature as,

Kieserite MgSO₄.H₂O

Epsomite MgSO₄.7H₂O (in certain gypsum deposits).

It is also present in certain mineral springs.

Laboratory Preparation

In laboratory, magnesium sulphate is prepared by dissolving magnesium, its oxide, hydroxide or carbonate in dilute sulphuric acid and evaporating the resulting solution, when colorless efflorescent crystals of the heptahydrate, MgSO4.7H2O, crystallize out.

It is less soluble in cold water but soluble on boiling.

Uses:

·         In medicine as mild purgative.

·         In industry as a weighing material for cotton and silk.

·         In fire-proofing fabrics.

·         As a filler for paper.

·         As a mordant- in dyeing and in tanning industry.

·         In the manufacture of soaps and paints.

health benefits of using Epsom salt

01.  Eases stress and relaxes the body

02.  Relieves pain and muscle cramps

03.  Helps muscles and nerves function properly

04.  Helps prevent hardening of arteries and blood clots

05.  Makes insulin more effective

06.  Relieves constipation

07.  Eliminates toxins from the body

Isochoric Process

 Definition

An isochoric process, also called a constant-volume process, an isovolumetric process, or an isometric process, is a thermodynamic process, in which the volume of the closed system is kept or held constant.

Fig: Isochoric Process

For an isochoric process, dV=0. In this process, the work done by the system is zero, i.e., W=0

Therefore from first law of thermodynamics, ΔQ = ΔU as the net work done Wisochoric = 0. Thus in an isochoric process, the total heat energy absorbed by the system is used to change its internal energy.

Isobaric Process

The term ‘Isobaric’ derives from the Greek isos(equal), and barus(heavy).  

An isobaric process is a thermodynamic process, in which the pressure of the working system remains/maintained/kept constant throughout the process.

In an isobaric process, dP=0. Hence, V/T is constant in an isobaric process.

          W =   PdV = PΔV = nRΔT(where n is number of moles)

In an isobaric process, there are typically internal energy changes, work is done by the system, and heat is transferred, so none of the quantities in the first law of thermodynamics readily reduce to zero.

 This is usually obtained by allowed the volume to expand or contract in such a way to neutralize any pressure changes that would be caused by heat transfer

Isothermal Process

Definition

'Isothermal' means at constant temperature. An isothermal process may be defined as follows, “An isothermal process is a thermodynamic process or change of a system,in which the temperature is maintained constant during supply of heat energy.”

Fig: Isothermal process

       In any isothermal process, ΔT = 0 and Q ≠ 0 . This typically occurs when a system is in contact with an outside thermal reservoir (heat bath), and the change occurs slowly enough to allow the system to continually adjust to the temperature of the reservoir through heat exchange.

       In such a case heat is allowed to flow from the surroundings into the system during expansion of gas, and taken out from the system to the surroundings during compression of the gas.

       An isothermal process is carried out by placing the system in a thermostat(constant temperature bath).

 Example

A practical example of isothermal process is some heat engines which work on the basis of the carnot cycle. The carnot cycle works on the basis of isothermal. 

Some extra info just to learn, not for exam 

•   In a strict sense, an isothermal process must be a reversible process because by definition, if every part of the system is at the same, constant temperature throughout the process, there can be no frictional or other irreversible effects giving rise to heat and causing local changes in temperature. No real process can be perfectly isothermal, some come very close, especially if it is accepted that it is only the spatially-averaged temperature which must remain constant.

•   In processes operating on a single phase, heat transfer will result in a change in temperature unless exactly balanced by some other energy transfer, e.g., work, and this balance can be very difficult to achieve in practice. One solution might be to eliminate the heat transfer: but in reality, insulation can reduce heat transfer but cannot stop heat transfer completely. An alternative approach is to use systems which can accept some heat transfer without a change in temperature.

•   In two-phase systems, heat transfer can be accommodated without changing the temperature by altering the relative amounts of the two phases present. The most common example is a phase equilibrium in a pure substance at constant pressure. Ice in water is frequently used as a fixed point for temperature because this system remains at a constant temperature provided the pressure is constant and the rate of heat transfer is not sufficient to cause the system to depart significantly from equilibrium.

Cyclic Process

Definition

Any thermodynamic process, in which any system goes from an initial state to a final state and then, returns back to the initial state, is called a cyclic process.

The net energy change in a cyclic process is zero. In this process since ΔU = 0.

            From first law of thermodynamics, ΔQ = W

            Thus in a cyclic process, the heat absorbed by the system is equal to the net work  done by the system.

Explanation 

Let us consider that a system changes from state A to state B, then back to state A again. For the change from A to B , ΔU1=Ub-Ua and for the change from B to A, ΔU2=Ua-Ub. The total energy change, ΔUtotal=ΔU1-ΔU2=(UB-Ua)+(Ua-Ub)=0

For a cyclic process, ΔH must also be zero as H is a state function.