Question

H2 reacts with the halogens (X2) according to the following reaction:
H2(g)+X2(g)?2HX(g)
where X2 can be Cl2, Br2, or I2.

Reactant/Product	?H?f(kJ/mol)	?S?f(J/mol?K)
H2(g)	0	130.7
Cl2(g)	0	223.1
HCl(g)	-92.3	186.9
Br2(g)	30.9	245.5
HBr(g)	-36.3	198.7
I2(g)	62.42	260.69
HI(g)	26.5	206.6

Part A: Calculate ?H? for the reaction between hydrogen and Cl2 at 293K .

Part B: Calculate ?S? for the reaction between hydrogen and Cl2.

Answer 1

Part A

H2 (g) + Cl2(g) ----------> 2 HCl(g)

Now,

( delta Hf )_rkn = (delta Hf)_products - ( delta Hf)_reactants

( delta Hf )_rkn = 2 * (delta Hf)_HCl - (delta Hf)_H2 - (delta Hf)_Cl2

But (delta Hf)_H2 and (delta Hf)_Cl2 = 0

So,

(delta Hf)_rkn = 2 * (delta Hf)_HCl = 2 * (- 92.3) = -184.6 kJ/mol

Part B

H2(g) + Cl2(g) -------> 2HCl(g)

delta So = 2*(delta So)_HCl - (delta So)_H2 - delta (So)_Cl2

delta So = 2 * 186.9 - ( 130.7 + 223.1) J/mol-K

delta So = 20 J/mol-K