Question Details

The equation of state of a gas is given by (P + aT²/V)Vᶜ = (RT +b) , where a, b, c and R are constants. The isotherms can be represented by P = AVᵐ - BVⁿ, where A and B depend only on temperature then

Options

A

m= -c and n = -1

B

m= -c and n= 1

C

m= -c and n = 1

D

m= c and n = -1

Correct Answer :

m= -c and n = -1

Solution :

The correct option is m = -c and n = -1.

Let us derive the given relation step-by-step from the equation of state.

The given equation of state for the gas is:

( P + a T 2 V ) V c = R T + b

We want to express this equation in terms of pressure P to represent the isotherms (where temperature T is constant). Let us first divide both sides of the equation by Vc:

P + a T 2 V = R T + b V c

We can rewrite the term 1Vc as V-c:

P + a T 2 V = ( R T + b ) V - c

Now, let us isolate the pressure P on the left-hand side:

P = ( R T + b ) V - c - a T 2 V

Using the exponent notation 1V=V-1, we obtain:

P = ( R T + b ) V - c - ( a T 2 ) V - 1

For an isotherm, the temperature T is constant. Therefore, the coefficients (RT+b) and (aT2) depend only on temperature. Let us define:
A=RT+b
B=aT2

Substituting A and B into the equation, we get the isotherm equation:

P = A V - c - B V - 1

Comparing this with the given standard isotherm form P=AVm-BVn, we match the exponents of V:
m=-c
n=-1

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