Question

7. Which reaction, with the following values of AH,
AS, at 400 K is spontaneous and endothermic?​

Answer 1

54 KJ > AH

Explanation:

Given,

T = 400 K

For endothermic reaction,

$AH>0$

Thus ,

$AG = AH -T AS$

If ,

$T AS>AH$ ,Then $AG<0$

Thus spontaneous,

$T \delta s = 135 \times 10^{-3} \times 400$

= $54 > AH$ KJ

Answer 2

Given the following values of  

Δ H  and  Δ S  for a reaction, select the only one that is spontaneous and endothermic.

( a )Δ H = − 50 k J ; Δ S = + 100 J / K   a t 400 K

( b ) Δ H =− 50 k J ; Δ S =− 100 J / K  at 400 k

(c) Δ H =+50KJ , Δ S=+100J/K at 600K

(d) Δ H=+50KJ ,Δ S=-100J/K at 400 k  

Explanation

Gibbs Free Energy:

• It is    denoted by G

• It is given by    G = H – TS

• It is state function  

• Extensive property  

       

It is defined as the amount of energy for a system that can be converted into useful work

It is obtained using by taking the difference between the change in enthalpy (H) of the reaction and the product of the change in entropy (S) and the absolute temperature (T) .

• For a reaction to be endothermic we have  
• Δ H > 0
• . For the reaction to be spontaneous we have  
• Δ G < 0

.The correct answer is :

( a )Δ H = − 50 k J ; Δ S = + 100 J / K   a t 400 K