Enthalpy change of formation

Using appropriate data from the 'Data Booklet'(the one they give with chemistry A level ) find the standard enthalpy change of formation of SiCl4 from the following equation.
Si (g) + 2Cl2 (g) ---- SiCl4 (g)

Well i dont know how to find the standard enthlapy of formation from the info given in the data booklet cuz the data booklet only gives the bond energies ..and i can find the enthalpy change by using the atomisation energies of Si and Cl2 but how do i find the enthalphy change using bond energies i.e from the data booklet cuz the data booklet does not give atomisation energies !!

Reply 1

Dekota

e-n-i-g-m-a

Using appropriate data from the 'Data Booklet'(the one they give with chemistry A level ) find the standard enthalpy change of formation of SiCl4 from the following equation.
Si (g) + 2Cl2 (g) ---- SiCl4 (g)

Well i dont know how to find the standard enthlapy of formation from the info given in the data booklet cuz the data booklet only gives the bond energies ..and i can find the enthalpy change by using the atomisation energies of Si and Cl2 but how do i find the enthalphy change using bond energies i.e from the data booklet cuz the data booklet does not give atomisation energies !!

Have you even heard of Hess's Law?

Reply 2

e-n-i-g-m-a

OP

yes i have but wat do i do about Si ..i mean theres no bon energy for simple Si as written in the equation ..

Reply 3

driving_seat

Where is this question 4m? Book or Past paper! If its 4m a book consult from it there must be appropriate bond energy given otherwise it would ve been in databooklet

as written in the equation Si is a gas and as such has no bonds...

... therefore no bond energy!

Reply 5

e-n-i-g-m-a

OP

charco

as written in the equation Si is a gas and as such has no bonds...

... therefore no bond energy!

well dats wat i assumed and then i solved it using the bond energies given in the data booklet and aplying the Hess's law.

Hf + 4(359) = 0 + 2(244)
and the naswer i get according to this equation is -948 KJ/mol which is wrong i think !!!

Reply 6

e-n-i-g-m-a

OP

hey is my method correct !!

Reply 7

farsofar

Here we have to use Hess's Law

Assume deltaH of ormation of SiCl4(g) as "x"

Si (g) + 2Cl2 (g) ----> SiCl4 (g)

4(Si-Cl4)=4(359)

Si (g) + 2(Cl-Cl)(g)

2(Cl-Cl) = 2(244)

Si(g) + 4 Cl (g)

No enthalpy change involved in bringing Si(g) at top to Si(g) bottom.
so Calculation goes as follows:

x + 4(359) = 2(244)

x = 2(244) - 4(359)

x = 488 - 1436

x=-948

Reply 8

Santikone

ok, I have new question? How to selectively remove only one Cl atom from SiCl4 at lowtemperature?