Question

An ideal gas at $${27^ \circ }C$$  is compressed adiabatically to $$\frac{8}{{27}}$$ of its original volume. The rise in temperature is $$\left( {\gamma = \frac{5}{3}} \right)$$

A. $${475^ \circ }C$$
B. $${402^ \circ }C$$
C. $${275^ \circ }C$$
D. $${375^ \circ }C$$  
Answer :   $${375^ \circ }C$$
Solution :
In an adiabatic process
$$p =$$  pressure
$$V =$$  volume
$$\gamma = $$  atomicity of gas
$$p{V^\gamma } = {\text{constant}}\,......\left( {\text{i}} \right)$$
Now from ideal gas equation,
$$\eqalign{ & pV = RT\,\,\,\,\left( {{\text{for}}\,{\text{one}}\,{\text{mole}}} \right) \cr & {\text{or}}\,\,p = \frac{{RT}}{V}\,......\left( {{\text{ii}}} \right)\,\left( {R = {\text{gas}}\,{\text{constant}}} \right) \cr} $$
From Eqs. (i) and (ii), we have
$$\eqalign{ & \left( {\frac{{RT}}{V}} \right){V^\gamma } = {\text{constant}} \cr & T{V^{\gamma - 1}} = {\text{constant}}\,......\left( {{\text{iii}}} \right) \cr} $$
So for two different cases of temperature and volume
$$\eqalign{ & {\text{So,}}\,\,{T_1}V_1^{\gamma - 1} = {T_2}V_2^{\gamma - 1} \cr & {\text{or}}\,\,\frac{{{T_2}}}{{{T_1}}} = {\left( {\frac{{{V_1}}}{{{V_2}}}} \right)^{\gamma - 1}}\,......\left( {{\text{iv}}} \right) \cr & {\text{Given,}}\,\,{T_1} = {27^ \circ }C = 27 + 273 = 300\,K \cr & {\text{Given,}}\,\,\frac{{{V_2}}}{{{V_1}}} = \frac{8}{{27}},\gamma = \frac{5}{3} \cr} $$
Substituting in Eq. (i), we get
$$\eqalign{ & \frac{{{T_2}}}{{300}} = {\left( {\frac{{27}}{8}} \right)^{\frac{5}{3} - 1}} \cr & {\text{or}}\,\,\frac{{{T_2}}}{{300}} = {\left[ {{{\left( {\frac{3}{2}} \right)}^3}} \right]^{\frac{2}{3}}}{\text{ or }}\frac{{{T_2}}}{{300}} = {\left( {\frac{3}{2}} \right)^2} = \frac{9}{4} \cr & \therefore {T_2} = \frac{9}{4} \times 300 = 675\;K = {402^ \circ }C \cr} $$
Thus, rise in temperature $$ = {T_2} - {T_1} = 402 - 27 = {375^ \circ }C$$

Releted MCQ Question on
Heat and Thermodynamics >> Thermodynamics

Releted Question 1

An ideal monatomic gas is taken round the cycle $$ABCDA$$   as shown in the $$P - V$$  diagram (see Fig.). The work done during the cycle is
Thermodynamics mcq question image

A. $$PV$$
B. $$2PV$$
C. $$\frac{1}{2}PV$$
D. zero
Releted Question 2

If one mole of a monatomic gas $$\left( {\gamma = \frac{5}{3}} \right)$$  is mixed with one mole of a diatomic gas $$\left( {\gamma = \frac{7}{5}} \right)$$  the value of $$\gamma $$ for mixture is

A. 1.40
B. 1.50
C. 1.53
D. 3.07
Releted Question 3

A closed compartment containing gas is moving with some acceleration in horizontal direction. Neglect effect of gravity. Then the pressure in the compartment is

A. same everywhere
B. lower in the front side
C. lower in the rear side
D. lower in the upper side
Releted Question 4

A gas mixture consists of 2 moles of oxygen and 4 moles of argon at temperature $$T.$$ Neglecting all vibrational modes, the total internal energy of the system is

A. $$4\, RT$$
B. $$15\, RT$$
C. $$9\, RT$$
D. $$11\, RT$$

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