Question

CH4(g)+4Cl2(g) —>CCl4(l) + 4HCl(g)

١.Methane reacts with chlorine gas to produce carbon tetrachloride and hydrogen chloride gas. Calculate the standerd entropy (d s) of the reaction and identify its spontaneity

2.calculate the standard molar enthalpy (delta H ) of the reaction

3.Explain if the reaction/process is always spontaneous,never spontaneous,or spontaneous only at high temperatures.(Hint: consider how delta H and deltaS influence delta G and spontaneity with the equation delta G =delta H -T deltaS )

Answer 1

CH4(g)+4Cl2(g) —>CCl4(l) + 4HCl(g)

DHrxn = (DH0f,CCl4 + 4*DH0f,HCl)-(DH0f,CH4 + 4*DH0f,Cl2)

       = (4*-92.31 + 1*(-135.4)) - (-74.8 + 4*0)

   = -429.84 kj

Dsrxn = (S0f,CCl4 + 4*S0f,HCl)-(S0f,CH4 + 4*S0f,Cl2)

         = (4*186.8 + 1*216.4)-( 186.2 + 4*223)

   = -114.6 j/mol.k

DG = DH-TDS

from the formula, if DG atleast = o ,the process is spontaneous.

0 = (-429.84*10^3)-(T*-114.6)

T = temperature = 3750.8 k

the temperature below 3750.8 k,the process is spontaneous.(at that conditions DG = -ve)

as 3750.8 k = 3477.65 C, is high temperature

answer: spontaneous only at low temperatures.