1

### JEE Main 2017 (Online) 8th April Morning Slot

For a reaction, A(g) $\to$ A($\ell$); $\Delta$H= $-$ 3RT.
The correct statement for the reaction is :
A
$\Delta$H = $\Delta$U $\ne$ O
B
$\Delta$H = $\Delta$U = O
C
$\left| {} \right.$$\Delta H\left| {} \right. < \left| {} \right.$$\Delta$U$\left| {} \right.$
D
$\left| {} \right.$$\Delta H\left| {} \right. > \left| {} \right.$$\Delta$U$\left| {} \right.$

## Explanation

Given reaction,

A(g)  $\to$  A($l$) ;

We know,

$\Delta$H = $\Delta$V + $\Delta$ng RT

Given, $\Delta$H = $-$3RT

From reaction,

$\Delta$ng = 0$-$ 1 = $-1$

$\therefore\,\,\,$ $\Delta$H = $\Delta$U $-$ RT

$\Rightarrow$ $\,\,\,$ $-$ 3RT = $\Delta$U $-$ RT

$\Rightarrow$$\,\,\,$ $\Delta$U = $-$ 2RT

$\therefore\,\,\,$ $\left| {\Delta U} \right|$ = 2RT

and $\left| {\Delta H} \right|$ = 3RT

$\therefore\,\,\,$ $\left| {\Delta H} \right|$ > $\left| {\Delta U} \right|$
2

### JEE Main 2017 (Online) 8th April Morning Slot

The enthalpy change on freezing of 1 mol of water at 5oC to ice at −5oC is :

(Given $\Delta$fusH = 6 kJ mol$-$1 at 0oC,
Cp(H2O, $\ell$ = 75.3J mol$-$1 K$-$1)
Cp(H2O s) =36.8 J mol$-$1 K$-$1)
A
5.44 kJ mol$-$1
B
5.81 kJ mol$-$1
C
6.56 kJ mol$-$1
D
6.00 kJ mol$-$1
3

### JEE Main 2017 (Online) 9th April Morning Slot

An ideal gas undergoes isothermal expansion at constant pressure. During the process :
A
enthalpy increases but entropy decreases.
B
enthalpy remains constant but entropy increases.
C
enthalpy decreases but entropy increases.
D
Both enthalpy and entropy remain constant.
4

### JEE Main 2017 (Online) 9th April Morning Slot

A gas undergoes change from state A to state B. In this process, the heat absorbed and work done by the gas is 5 J and 8 J, respectively. Now gas is brought back to A by another process during which 3 J of heat is evolved. In this reverse process of B to A :
A
10 J of the work will be done by the gas.
B
6 J of the work will be done by the gas.
C
10 J of the work will be done by the surrounding on gas.
D
6 J of the work will be done by the surrounding on gas.