1

### AIPMT 2000

For the reaction,
C2H5OH(l) + 3O2(g) $\to$ 2CO2(g) + 3H2O(l)
which one is true
A
$\Delta$H = $\Delta$E $-$RT
B
$\Delta$H = $\Delta$E + RT
C
$\Delta$H = $\Delta$E + 2RT
D
$\Delta$H = $\Delta$E $-$ 2RT

## Explanation

As we know, $\Delta$H = $\Delta$E + $\Delta$ng RT

Now, $\Delta$ng = Number of gaseous moles of products – number of gaseous moles of reactions

= 2 – 3 = – 1

$\Rightarrow$ $\Delta$H = $\Delta$E + (–1) RT

$\Delta$H = $\Delta$E – RT
2

### AIPMT 2000

The entropy change in the fusion of one mole of a solid melting at 27oC (latent heat of fusion is 2930 J mol–1) is :
A
9.77 J/mol-K
B
10.77 J/mol-K
C
9.07 J/mol-K
D
0.977 J/mol-K

## Explanation

$\Delta S = {{\Delta H} \over T}$

= ${{2930} \over {300}}$

= 9.77 J/mol-K
3

### AIPMT 2000

2Zn + O2 $\to$ 2ZnO;  $\Delta$Go = $-$ 616 J
2Zn + S2 $\to$ 2ZnS;  $\Delta$Go = $-$ 293 J
S2 + 2O2 $\to$ 2SO2;   $\Delta$Go = $-$408 J
$\Delta$Go for the following reaction
2ZnS + 3O2 $\to$  2ZnO + 2SO2 is
A
$-$ 731 J
B
$-$ 1317 J
C
$-$ 501 J
D
+ 731 J

## Explanation

2Zn + O2 $\to$ 2ZnO;  $\Delta$Go = $-$ 616 J ....(1)
2ZnS $\to$ 2Zn + O2;  $\Delta$Go = $+$ 293 J.....(2)
S2 + 2O2 $\to$ 2SO2;   $\Delta$Go = $-$408 J .....(3)

$\Delta$Go for the reaction can be obtained by adding (1), (2) and (3)

$\therefore$ $\Delta$Go = 293 - 616 - 408 = -731 J
4

### AIPMT 2000

Cell reaction is spontaneous when
A
$\Delta$Go is negative
B
$\Delta$Go is positive
C
$\Delta$Eored is positive
D
$\Delta$Eored is negative

## Explanation

For spontaneous reaction $\Delta$Go = – ve and

Eocell = + ve

as $\Delta$Go = – nFEocell

where, n = number of electrons taking part

Eo = emf of cell